AirForce Texan: Part 5

by Tom Gaylord
Writing as B.B. Pelletier

Texan
AirForce Texan big bore.

Part 1
Part 2
Part 3
Part 4

This report covers:

  • Upgrade to the TX2 valve?
  • Mr Hollowpoint
  • The day
  • Mr. Hollowpoint 333-grain bullet
  • Stretching the air
  • Cold!
  • First two bullets
  • Time to refill
  • Summary

The .458 Texan from AirForce Airguns I’m testing has been with me for many years. Mine is from the first production run. And AirForce has made significant changes to the rifle in the time since mine was made (read Part 3, where the new TX2 valve is discussed), but I don’t care. My rifle still hits hard and drills heavy bullets where I want them to go.

Upgrade to the TX2 valve?

AirForce offered to upgrade my Texan to the new TX2 valve if I wanted. I would gain additional power from the new valve, plus with the new carbon fiber air tank I would retain the 4+ good shots, because even though the new valve uses more air, the CF tank it’s in gets filled to 250 bar/3,626 psi. I could also switch over to the new barrel that is just as long as mine, but has a faster 1:30 twist rate that stabilizes the heavier bullets better. My 535 foot-pound rifle would become a 700 foot-pound rifle with the heaviest bullets.

I don’t know if I want to upgrade or not. My rifle has proven deadly accurate already with a 215-grain semi-wadcutter from Tin Starr bullets. It put 6 of them into about 1.5-inches at 100 yards. And it doesn’t take 700 foot-pounds to dispatch a whitetail deer or a feral hog.

Texan big bore best group
Remember, we measure from the center of the 2 holes farthest apart. Those two radii equal 1 bullet diameter (center-to-edge equals one radius). So, subtract one bullet diameter (.458″) from the measurement shown on the calipers and you get the center-to-center measurement. The group measures 1.506-inches, center-to-center.

If, on the other hand, I did upgrade I would be testing an entirely new air rifle, because both the barrel and the powerplant would be different. To work properly with the TX2 valve the internals of my powerplant would also have to be changed.

In Part 4 I tested my unaltered rifle, using the new TX2 tank and valve. My rifle’s best power had been 535 foot pounds. But now, with the new valve and a Mr. Hollowpoint 490-grain bullet, the power jumped up to 655 foot pounds on the first shot. And that was without the powerplant modifications my rifle needs to do its best with the new valve.

I’m the guy who always says, “Never get rid of an accurate airgun.” Is that what I would be doing if the changes were made? I want to hear what you think. Now, let’s get on with today’s report.

Mr Hollowpoint

Robert Vogel, who is Mr. Hollowpoint to big bore shooters, sent me an assortment of his bullets to test in my Texan. I showed you four of them in Part 4, last November. My thoughts were to select the one or two best performers, tune the power adjustment wheel to optimize the rifle to that bullet — and then leave it alone. 

In Part 4 I tested four of the five bullets he sent. Today I will test number five. I’ll also go back to the bullet that has proven to be the most accurate previously and see if it still as good as it was in Part 4. Remember from Part 4 that I asked him to size all the bullets 0.458-inches, because that’s the size with which my rifle does its best.

The day

I shot the Texan last Friday at the rifle range with reader Cloud9, who is still testing his RAW field target rifle. We were on the 50-yard range that is covered and has nice concrete shooting benches. But my first test that day was the BSA R10 Mark II, and I shot a lot of 10-shot groups with it. You’ll see that one tomorrow.

The day was a cold Texas day. The temperature wasn’t that bad, but the wind was chilling both me and Cloud9 to the bone. By the time I got to the Texan I had already been shooting for almost 2 hours and was pretty cold. 

Mr. Hollowpoint 333-grain bullet

First I will test that last bullet that Mr. Hollowpoint sent. It’s a long 333-grain bullet with a deep hollow point and wide grease grooves that are separated by narrow bands. It looks different enough from all the other bullets I’m testing that I decided to save it for last.

Mr. Hollowpoint 333-grain bullet
The 333-grain bullet from Mr. Hollowpoint looks quite different from all the others.

The first bullet landed in the bull because the rifle was still sighted in from last November. When the second, third and fourth bullets also struck black I thought maybe this would be one to consider — especially for shots at close range. Those first 4 shots grouped in 1.405-inches between centers at 50 yards.

Stretching the air

Then I tried to take a fifth shot without refilling. The onboard pressure gauge read 2,000 psi before the shot and I knew I should refill, but I thought I would take a chance. That fifth bullet landed 2-1/2-inches below the lowest bullet that was already in the bull. It was still in line with the group above, just much lower. It opened the first 5 shots to 3.838-inches at 50 yards.

At this point I refilled the rifle to 3,000 psi and took a final shot. If it went into the first group I would know that 4 shots are all I can get from this 333-grain bullet on a fill to 3,000 psi. 

Well, it did go to the first group, but it landed higher, opening those first four shots to 2.308-inches at 50 yards. Obviously I’m disregarding the lower fifth shot from the first fill in this measurement.

333-grain bullet group
The first 4 shots all hit the bull and grouped in 1.405-inches at 50 yard. The fifth shot on that fill dropped lower, opening the first five shots to 3.838-inches. By filling the tank again, I fired a sixth shot that hit above the first four. That group of 5 shots measures 2.308-inches between centers. Sorry for the blurry image.

Cold!

My little fingers were getting really cold by this time, so I knew I didn’t have much more time remaining. When you see all that I shot with the BSA R10 Mark II you’ll understand how long it took me to get to this point.

I wanted to give the most accurate of the five Mr. Hollowpoint bullets one final chance to see if it was still as accurate as it had been back in November. That was the 300-grain hollowpoint. Back then I put five of them into 1.232-inches at 50 yards, with three of them in 0.349-inches. Could I still do as well on this frigid day? And if I could, maybe I could adjust the power adjuster to optimize it.

Mr. Hollowpoint 300-grain bullet
Mr Hollowpoint 300-grain bullet that you have seen before is the most accurate of all his bullets that I’m testing.

First two bullets

Since I had just filled the Texan for the last shot with the 333-grain bullet, it still had a lot of air, so I decided to shoot the first couple 300-grainers before refilling. Shot number one nicked the top of the bull at 50 yards. Shot two, however, could not be seen clearly through the UTG 6-24X56 SWAT scope. My Meopta MeoPro HD 80 Spotting Scope, however, revealed that the second shot had gone through the same hole as the first shot. I thought that was what I was seeing through the UTG scope, but I needed confirmation. You can see it in my photograph.

Time to refill

At this point I wanted nothing to spoil this group, so I refilled the rifle to 3,000 psi. Shot three landed apart from the first two shots, but it was very close. Shots 4 and 5 are clustered with it. This five-shot 50-yard group measures 0.659-inches between centers!

Back in 2015 I shot five shots into 0.762-inches at the same 50 yards. Those were the same bullets that made a 1.5-inch 100-yard group.

Texan big bore best group
Back in 2015, I managed to put five 215-grain bullets into 0.762 inches at 50 yards. This was clearly a good bullet!

300-grain bullet group
Last Friday, five 300-grain bullets made a 0.659-inch group at 50 yards. This bullet from Mr. Hollowpoint has edged out the Tin Starr bullet from 2015. Will it do as well at 100 yards?

Well, there is no way that I am fooling with the power adjuster after shooting a group like this. This Texan is sighted-in for 0-75 yards right now with this bullet!

Summary

My current Texan is very accurate and as powerful as I need it to be. But by allowing AirForce to upgrade it to the new TX2 valve and the new barrel, I would have a brand new airgun to test. I’m leaning in that direction, but I would like to hear what you readers think.

As it stands now the 300-grain bullet from Mr. Hollowpoint is extremely accurate. I do think I need to test it at 100 yards before I do anything to the .458 Texan.


Big Bore airgun calibers

Tom Gaylord
Writing as B.B. Pelletier

This report covers:

  • The greater problem
  • The beginning
  • Bullets — not pellets
  • .308 caliber
  • Bore size
  • .357 caliber
  • Black powder
  • The .45 caliber dilemma
  • Shoot soft lead bullets that are slightly larger
  • Other big bore calibers
  • Summary

Most shooters are familiar with the smallbore airgun calibers of .177, .20, .22 and .25. Even shooters who don’t consider themselves to be airgunners know at least the .177 and .22 calibers. But in recent years there has been an explosion of big bore airgun calibers, and I am seeing that many shooters have little knowledge about them. If that were the only problem it would fix itself, because over time people always learn.

The greater problem

The bigger problem are the airgun manufacturers that do not know much, if anything, about the larger calibers. This report will address the lesser-known truths about big bore airgun calibers.

The beginning

Where do the big bore calibers start? Well, they start at anything above .25 caliber. But there is a big bore caliber called .257 that is a legitimate .25 caliber. The difference is the .257 big bore shoots elongated bullets rather than diabolo pellets. Instead of 45 grains they can weigh 100 grains and more. They can reach out hundreds of yards, where the wasp-waisted hollow-tailed diabolo falls off fast after just 100 yards.

Bullets — not pellets

Another thing is big bore airguns shoot bullets, for the most part — not pellets. Yes, there have been some .308, .357 and even .45-caliber diabolo pellets made for certain airguns, but big bore airguns have been around since about the year 1350 and they have always used bullets — round balls until around 1850 and conical lead bullets since then. The diabolo pellet is a 20th-century invention.

.308 caliber

Recently the .308-caliber big bore has gained a lot of traction in the marketplace. People hear the caliber size and envision the .308 Winchester cartridge that they know is very powerful. But a .308 caliber pellet driven by air is far less powerful. It gives up the one big advantage of the big bore airgun — size. With a .308 air rifle your shot has to be precise or you risk wounding your quarry. That said, the .308 can do the job for a good shooter.

Bore size

Now let’s consider bore size for a moment. You don’t have to do that with a pellet. A .22-caliber pellet should work in most .22-caliber airguns. Accuracy will differ from pellet to pellet and we sometimes sort pellets by the diameter of their head, but that’s as far as it goes. Not so for big bore bullets! And this is where shooters new to the shooting sports get confused.

A .308 bullet may be very accurate in a .308 big bore airgun, or it may not even stabilize. That gun may need a bullet that’s .309-inches in diameter to work well. It all depends on the size of the bore! You see, smallbore airgun barrels are closely controlled to fit the pellets of their caliber. But big bore airguns can have barrels of widely varying internal sizes. That’s because there are no set standards for barrels of big bore airguns. They tend to be firearm barrels that have been used on airguns.

There are exceptions, of course. AirForce Airguns, for example, orders hundreds of barrels in each big bore caliber they produce from Lothar Walther. They are such a large customer that they can specify the exact inside dimensions, as well as the rifling twist rate. That’s something that Joe from Podunk, who makes 50 rifles a year, can’t do. He has to select his barrel from the stock items a barrelmaker offers.

.357 caliber

The next size up from .308 is .357 — and this caliber is a huge problem! Ten years ago it was called 9mm, which is sized 0.355-0.356-inches in diameter. The Koreans who were the first to make rifles in this caliber made them with barrels sized for 9mm lead bullets. The trouble with that is, unless you know where to look, it’s very hard to find 9mm lead bullets. That’s because 9mm is mostly a pistol caliber. All the bullets that are popular for 9mm pistols are jacketed and don’t do well in airguns — especially not the underpowered Korean ones! It took a full decade for the airgun makers to realize their mistake, and it took dealers and shooters even longer. Even today there are many shooters who think one-thousandth of an inch shouldn’t matter that much with a bullet. But it does!

Black powder

This is where a background with shooting black powder firearms comes in handy. There are two big reasons for this. First, when black powder explodes upon firing, the instant high pressure upsets the base of lead bullets, obturating (squashing) them into the bore. They are squashed into the rifling where they fit the bore better and also seal against the burning gasses. Airguns cannot do the same, so the fit of the bullet to the bore is critical from the start.

The second reason a black powder background or at least a knowledge of their history is important is because in the past (1250 A.D. to 1900) all non-military firearms (read that as black powder, because that’s all there was for most of that time) came with bullet molds when they were made. The owner had an idea of his gun’s caliber but it didn’t matter as long as he used the mold that came with it to cast his bullets. The military held gun makers to more exacting specifications so they could produce the bullets for their soldiers. Their guns didn’t have to each come with a mold.

Today, though, black powder arms are produced to more exact specifications, so their owners can purchase bullets to go with them. But it still isn’t a smooth road.

The .45 caliber dilemma

Now we come to one of the biggest dilemmas in big bore airguns today — the .45 caliber that exists in no less than three distinct sizes! And they are not interchangeable. Starting with the Koreans again, when they made .45 caliber big bores they made their barrels for bullets of a diameter of .452-inches. That is the modern .45 pistol diameter for the .45 ACP cartridge. And some .45 Colt revolvers also have bores that size. 

Bullets made in that size are expected to be fired from .45 caliber handguns at 850 f.p.s. or so. They weigh from 160 grains to 250 grains — AND THAT IS IT! If they are shot in big bore air rifles in the 200-225 foot-pound class, they are fine.  The Turks are also making their .45 big bores with bore diameters in this size. I have no idea of what the Chinese who make the big bores for Gamo are doing, but it does bear consideration.

The next popular size of .45-caliber bullet is .458, and it has another problem. Some makers are calling their rifles a .457, but I doubt you will find bullets of that size unless they are custom made. Don’t worry, though, because .458 bullets are what you want to use anyway. They fit the bore, where .457 bullets usually don’t.

These are the air rifles that shoot bullets weighing 350-500 grains. They will also shoot the lighter bullets, as long as they are sized .458 and not .452.

Then there are the big bore rifles that are made by boutique makers who turn out a few guns a year, in caliber .454. These guys don’t last that long and finding bullets for their rifles can be a real chore. This size was for Colt Single Action Army revolvers from decades ago. You’ll have to go to a custom bullet maker to buy them today.

So — they’re all .45 caliber, but in three different sizes! Did you know that? If you didn’t and you shoot your rifle with the wrong size bullet you aren’t going to do very well. A 24-inch group at 100 yards can shrink to a 3-inch group, just by using bullets of the right size!

Shoot soft lead bullets that are slightly larger

So—the lesson today is to shoot lead bullets of the right diameter. The right diameter is one-thousandth over the bore diameter in most instances. But you need to experiment with different sizes to make certain. I have been doing this for over 50 years and in my experience a thousandth larger with a lead bullet is what you want.

They should be soft lead bullets, because hard cast bullets will leave lead deposits in the bore. Air rifle bullets also don’t need to be lubricated — as long as they are soft lead. In fact they shouldn’t be. They are ideal for the velocities at which the most powerful of these air rifles shoot — generally 700-900 f.p.s.

Other big bore calibers

Yes there are big bores in calibers other than the ones mentioned here. A number of rifles in .40 caliber have been made, but they were all made by low-rate or custom makers who probably made them to work with a lead bullet that is commonly available. 

That being said, there can be big bores in other calibers, as well. I know of several big bores made to shoot the 12 gauge rifled slug that looks like a diabolo pellet. It’s called the Balle Blondeau.

Balle Blondeau
The Balle Blondeau is a 12-gauge slug that looks like a diabolo pellet. Some smoothbore big bores have been made to shoot it.

Like black powder arms, a big bore airgun can be made in any caliber. If you plan to buy one, make sure you can get the bullets for it first.

Summary

This has been a brief but fairly complete look at big bore projectiles. I have concentrated on the bullets rather than the few diabolo pellets that exist, because the bullets are where it’s at for big bores. Stay tuned.


AirForce Texan: Part 3

by Tom Gaylord
Writing as B.B. Pelletier

Texan
AirForce Texan big bore.

Part 1
Part 2

This report covers:

  • TX2 valve for .45 and .50 caliber Texans
  • Old rifle, fresh test
  • “New” bullets
  • The TX2 valve
  • Power setting
  • Seat the bullet in the rifling!
  • Velocity
  • One more velocity lesson
  • Summary

After writing Part 2 of this report last week I went to AirForce last Friday morning and spent a couple hours with Ton Jones, talking about the Texan and the new TX2 valve and carbon fiber tank. I took my Texan that was made in the first production run, and we attached the new tank to it. That answers the first question — does the new tank fit older Texans?

AirForce Texan Ton Jones
|Ton Jones set up my .45 caliber Texan with the new carbon fiber tank and the TX2 valve.


The TX2 valve boosts power and currently only the .45 and .50 caliber Texans work with it. There is also a difference between the valve cap on the .45 and the .50 caliber valve, so to use the same tank on both airguns the cap needs to be exchanged.

Old rifle, fresh test

Reader Chris USA mentioned that my last report on the Texan was in August of 2015. Yes, it was. The accuracy and velocity data I have given you thus far came from those reports. Since there is a new tank and valve, I conducted new velocity testing with my same rifle and a new tank last Friday. I will cover that later in this report.

“New” bullets

Chris also suggested that I try some of the “new” lead bullets that are being made for the Texan. I hope to do a little of that, but since conical lead bullets are 160 years old, there isn’t really anything I haven’t seen. I think what Chris is really asking for are my comments about some of the bullet makers who are in the market. What I see is a lot of guys who don’t know lead bullets are responding to things the sellers are telling them.

Twist rate

Well, one thing I learned last Friday was the newer Texans come with a barrel that has a twist rate of one turn in 30 inches. They have done this to accommodate the heavier bullets people seem to use. I don’t know what the twist rate is in my barrel and AirForce asked if I wanted to change over, but my rifle is so accurate now that I want to leave it as it is.

The TX2 valve

The TX2 valve is unique in that is has no spring to push it closed. It relies on air pressure alone to do that.

Power setting

In Part 2 I showed the power setting I used for my tests in 2015. Well AirForce has changed the power setting mechanism and Ton told me my rifle was set wrong for the TX2 valve. The index mark needs to be between the first and second notch on the right for heavier bullets and never past the second mark for anything. Since heavier bullets remain in the barrel longer than light ones, They maintain back pressure against the firing valve — holding it open longer.

 So we set it as high as it would go. That means the most spring tension on the striker. On newer guns you may lose sight of the index mark when you reach the end of the adjustment range.

Texan power setting

The power adjustment wheel is turned as far to the right as it will go — putting maximum tension on the striker spring. This was set for the lightest bullets we tested.

TexanSS bullet tuner
These are the power settings on the Texan power adjustment wheel. According to Ton Jones you should never go lower than the second mark that’s shown as 3/4 power in this picture when using the TX2 valve. You want to make that setting your lowest point for the standard tank, as well.

Seat the bullet in the rifling!

If there was one big mistake I made in part 2 it was showing you a bullet laying in the loading trough and telling you that the bolt would push it home. Well, it doesn’t work that way. I’ve gone back and corrected the language in Part 2 and now I have to tell you how important it is to manually seat each bullet into the rifling. I knew that from testing the TexanSS in 2018, but for some reason I reported it wrong in Part 2 of this report. And some bullets present problems, as well. For example, the semi-wadcutters that were the most accurate in my Texan want to enter the breech tipped on an angle unless they are pushed into the rifling. Their angled nose is the reason for this. Once the front band of the bullet encounters the rifling, it squares up the bullet with the bore and everything is okay. You also get more consistent velocity that way.

TexanSS bullet seated
Ton Jones seats a bullet into the Texan rifling. If you can stand the rifle up and the bullet stays in the breech, it’s seated okay.

TexanSS semi-wadcutter
The slanted nose on this semi-wadcutter bullet makes it want to tip over when seated into the Texan breech.

TexanSS semi-wadcutter seated
Once the front band of the semi-wadcutter bullet was in the rifling, the bullet was square with the bore.

Ton took me outside and let me listen to a shot with a well-seated semi-wadcutter. It bellowed , which is how you know it’s seated right. And I heard the bellow through my electronic noise-suppression headphones.

Velocity

Okay, I said that the TX2 valve gives fewer shots than the standard valve. Let’s see. We’ll check the velocity with a 490-grain flat nose bullet made by Mr. Hollowpoint — Robert Vogel. There you go, Chris!

The tank was filled to 3600 psi and the gun was fired. The bullet went out at 776 f.p.s. That’s 655 foot-pounds at the muzzle. We topped it off a second time and the next bullet went out at 778 f.p.s. for 658.74 foot-pounds. This time we did not refill the tank. 

Shot……Vel.
2………..763
3………..731

The tank registered 2590 psi after three shots. We then went outside and Ton fired shots 4, 5,6, and 7. On shot 7 there was a partial tank dump and on shot 8, with just 800 psi showing on the gauge before the shot, the tank dumped all its air. I would say shots 4 through 7 were good enough for finishing shots on game that was down.

One more velocity lesson

Ton filled the tank to 3,600 psi and loaded and shot a 210-grain bullet. It went out at 620 f.p.s. That left 3300 psi in the tank. He told me to watch what happened to the velocity as he shot more.

Shot……Vel.
2………..660 
3………..726 3130 psi remains
4………..795 3050 psi remains

Velocity is increasing as tank pressure drops since there is no valve return spring to close the valve. Want a lot of shots from a big bore? Here they are! And, if you want to increase the velocity — reduce the pressure in the tank!

Summary

We’re just getting started with the Texan. It’s a big bore with performance you can stretch! I have a lot more to tell so don’t go away.


What’s wrong with solid “pellets”?

by Tom Gaylord
Writing as B.B. Pelletier

This report covers:

  • Diabolo pellet
  • The couch coach solution
  • Tradeoffs
  • Summary

Today’s report was engendered by yesterday’s report about the AirForce Texan big bore air rifle. Many of you have been discussing the advantages of solid pellets over diabolos

Today I’d like to look at this question a little closer. For starters, let’s call solid pellets what they really are, which is bullets.

pellet bullet
A diabolo pellet on the left and a bullet on the right. Let’s call them what they are!

In the 1880s pellets were either solid lead or they were lead with felt glued onto their bottom. In flight the felt caught the air and slowed the slugs down, keeping their nose pointed  forward. Just after the turn of the 20th century the invention of the diabolo pellet changed pellets forever.

felted slugs
A felted slug has a small piece of felt glued to the bottom to provide air drag in flight.

Diabolo pellet

The diabolo pellet was named after the diabolo — a European juggling device.

diabolos
A diabolo is an object jugglers use. The pellet takes its name from them.

diabolo pellet
The diabolo pellet is far better ammunition for a pellet gun.

The wasp waist and flared hollow tail of the pellet create drag and push the weight forward — all to increase stability in flight. Bullets don’t do that. To stabilize a bullet you have to spin it on its long axis. The longer the bullet is, relative to its width (caliber), the faster it must be spun.This can be done in one of two ways. Either push the bullet faster or increase the rate of the rifling twist.

A .223 bullet weighing 55 grains and fired at 3,000 f.p.s. through a barrel with a 1 twist in twelve inches leaves the muzzle spinning 180,000 rpm. (that’s 3,000 times 60 seconds)That turns out to stabilize the bullet good enough for a couple seconds of flight to perhaps 300-yards. Now, to drive a bullet of that caliber and weight that fast takes a cartridge that produces about 55,000 psi of pressure. 

But a longer bullet of the same caliber that weighs 69 grains will need a twist rate of one turn in 8 inches. That’s one and one-half revolutions for every foot it travels. There is no way you can drive a bullet of that caliber and weight to 3,000f.p.s., so the twist rate needs to be increased to compensate for the loss of velocity. Pushing it out the spout at 2,700 f.p.s. gets a spin rate of 243,000 rpm, which stabilizes the bullet long enough to fly for almost 6 seconds. The heavier bullet goes slower but remains stable longer and is thus accurate even farther.

These are the games you play with bullets. And you want them to work in airguns?

The couch coach solution

Okay, someone says. If that’s that case I want a .357 big bore with a twist rate of one turn in one inch! A 700 f.p.s. rifle will get the bullet spinning 700 times 60, or 42,000 rpm.

No — it won’t. If an air rifle operating at 3,000 psi can push a 158-grain lead bullet out the muzzle at 700 f.p.s., it does it through a barrel that has a 1:16″ twist. Go to a 1:1″ twist and the exit velocity drops to 250 f.p.s. — if the gun even works at all! To go out at 700 f.p.s. you need 11,000 psi behind the bullet. Try to find that!

Tradeoffs

This is where a knowledge of black powder shooting really pays off. You soon learn there are limits you can’t get past and you have to learn to operate within those limits. Want to take bigger game? It may not be with higher velocity but with a heavier bullet of larger caliber. Well — isn’t that a lot like airgunning? Sure you can shoot a pellet at 1,300 f.p.s., but it gets you nothing because you can’t hit what you shoot at! But if you shoot at 850 f.p.s. and learn to hit everything, then you have the world on a string!

Summary

It’s easy to design the perfect universe where the $300 air rifle puts 10 pellets into 0.15-inches at 25 yards and therefore 0.30-inches at 50 yards and 0.60-inches at 100 yards and so on… But that ain’t the real world.

Said another way, leave the solid pellets to the big bore airguns and firearms.


Ballistic coefficient: What is it? Part 2

by Tom Gaylord
Writing as B.B. Pelletier

Part 1

This report covers:

  • Review
  • Today’s discussion
  • Round balls
  • Conical bullets
  • Smokeless powder
  • A big point
  • Shape
  • Round balls — again
  • The bottom line

I’ve taken 11 months to return to this subject of ballistic coefficients (BC). That was in spite of some tremendous interest in Part 1 of this report last May.

I’m purposely avoiding all discussion of mathematics, which is difficult, since ballistics is a discipline that heavily employs mathematics. But I’m not qualified to write about the math; and, more importantly, I know that 99 percent of my readers would be turned off if I were to write the report that way.

Review

Last time we learned that the BC of a pellet:

• Is an extremely small decimal fraction compared to the BC of a conical bullet.
• Varies with the velocity of the pellet.
• Varies with the shape (form) of the pellet.

We also learned that the stated BC of a pellet can be forced to vary by where the measurements are taken.

We understand that diabolo pellets are designed to slow down rapidly in flight, and that the BC is a measure of the velocity retained in flight. So, a pellet’s BC rapidly changes over a short distance.

We learned that a pellet’s BC varies between 0.010 and 0.045. We also learned that pellets that have a relatively high BC (the larger numbers) will never slow down faster than pellets that have a relatively low BC. Even though all diabolo (wasp-waisted with a hollow tail) pellets rapidly slow down, the higher BC numbers are given to the pellets that slow down the least in relation to all diabolo pellets.

Today’s discussion

Today, we’ll look at the impact that shape (form) has on the BC. We’ll also look at the impact velocity has on the BC. Let’s begin with that.

Round balls

When firearms were first invented (we now believe that was in the 1300s), the earliest formal shape for missiles was either a shaft (arrow or dart) or a ball. The earliest projectiles were probably just stones, but that soon gave way to uniform lead projectiles that were easy to shape. Cannon balls were still chiseled from tough rock for many years before they, too, were cast from iron into spheres.

The round ball became more than just a projectile of choice. It became synonymous with the title — bullet. From some time in the 1400s to around 1840, the word bullet meant a round ball. Round balls are easy to enter into formulas and ballistics tables because the form is always the same. The weight varies, but not the form (shape). Because of this, the early science of ballistics was built around a spherical bullet, and everything was fine.

Conical bullets

Conical bullets (oddly referred to as conical balls in their early days) changed everything. Ballistics had to expand to adapt to these new projectiles. Several ballisticians worked out new formulas to account for the different new forms, but by now the forms were changing faster than the science could keep up.

Smokeless powder

Then, smokeless gunpowder came on the scene and things changed again. Velocities with black powder (which, up to that time was just called gunpowder) topped out somewhere around 1,600 f.p.s. Within 20 years, smokeless power doubled that speed; and in another decade, it added another thousand f.p.s. Suddenly, bullet makers had to be concerned with shapes that flew at ultrasonic velocity. This was decades before anything else approached that speed, so things like wind tunnels weren’t even available for modeling.

It may seem like I’m getting far from the topic, but here’s why I am telling you this. In 1870, the Rev. Francis A. Bashforth — the inventor of the first (?) electronic chronograph — discovered that drag increases with the square of the velocity at speeds between 430 f.p.s and 830 f.p.s. — but with the cube of velocity at speeds between 830 f.p.s. and 1,000 f.p.s.! That higher range is the trans-sonic region that we tell airgunners to be wary of. We used to think it caused inaccuracy, but I disproved that in 2011 in an 11-part blog series titled Velocity versus accuracy. But what it definitely does do is increase the rate at which projectiles slow down.

I could easily get into a discussion of the ideal shape for supersonic projectiles, and there are many airgunners who would like that. “Just design a solid pellet that has a boattail, and all your problems are solved,” they say. Yes, all problems are solved, save one — accuracy. No airgun I know of is capable of accurately shooting those solid pellets (that I’ll now call bullets) at supersonic speeds. In fact, very few airguns can get them up to supersonic speeds at all! So, the discussion is over before it begins.

A big point

If something can’t be done, it makes very little sense complaining about what “they” should do. The blog readers know that I’m not a negative person. I’m willing to try anything that has a chance of success. But physics is physics! I’ve learned in all my experiments and reading that airguns have practical velocity limits. We may not be at the limit today, but we’re very close. Because, to push a pellet any faster than about 1,500 f.p.s. (1,486 f.p.s. is the fastest pellet I’ve ever observed), requires us to do things with compressed air that it just doesn’t want to do. The speed of sound governs how fast air can flow. Pellets can be pushed faster than the speed of sound; but to go much beyond 1,500 f.p.s., we’re going to have to use a different compressed gas.

So, pellets that top 1,000 f.p.s. are slowing down at least at the cube of their velocity. That’s what Bashforth tells us. Take another look at the chart I showed you in Part 1:

BC chart

This is how velocity affects a hypothetical heavy domed pellet.

The chart isn’t real, which means it wasn’t generated by actual test data, but the relationship of the BC decline at the trans-sonic region is representative. Lighter pellets fall off their BC at lower velocities, so take the entire curve and move it to the left. The same thing happens — just at lower velocities. Heavier pellets fall off at higher velocities, too. But all of them fall off in the same way.

Shape

Enough talk about velocity; now let’s look at what the shape (form) of a pellet does to the BC. Just as certain shapes work well at supersonic speeds, there are also good shapes for subsonic speeds, where most pellets live. A domed nose with a solid cylindrical body is very good at subsonic speeds. And the more it weighs, the higher the BC will be.

pellets
The shape or form of the pellet has a lot to do with the ballistic coefficient.

The wadcutter, by contrast, is the worst shape — or at least it’s down there withe the worst of them. Some people feel that hollowpoint pellets are even worse because their hollow points act like air brakes. Others believe the hollows fill with air under pressure, and the pellets then act like wadcutters.

The pointed pellet is not as aerodynamic as its shape seems. While it looks sleeker than a dome, it doesn’t turn out to work that way at subsonic pellet velocities. A point is great for supersonic speed, but it does very little below the speed of sound. Pointed pellets do penetrate deeper in solid media; but in the air, they aren’t that different from domes.

Round balls — again

Round balls — remember them? As it turns out, a round ball is sleeker at subsonic velocities than any diabolo pellet. Only when the pellet weighs considerably more than a ball of the same caliber (and may be too heavy to shoot effectively) will it have a superior BC. Round ball BCs hover around the 0.07 mark. That’s about double what the best diabolo pellet offers and several times what the average diabolo has.

So, why not just shoot round balls? Simple answer — accuracy. Round balls don’t have any accuracy at longer distances. The high drag of the diabolo pellet — the very thing that destroys their BC — is also what helps them be so accurate.

The bottom line

Yes, the BC of a pellet is important, but only after you know that it’s accurate. If you can’t hit what you’re shooting at, the retained velocity of your pellet means nothing.

So, search for accuracy first and a high BC second. Or, in some cases, such as long-distance hunting, look among the pellets with high BC numbers for the one that’s the most accurate. Don’t just shop for the highest BC unless you also understand the relationship of your gun to that number (re-read Part 1 to understand).

Is that all there is? Of course not. We could go on and talk in more detail about form, but I think the basics have been covered.

I know that many of you use the Chairgun program and find it very useful. One of the things Chairgun requires is the input of the BC of the pellet in question. Sometimes, you only discover how close that BC is after shooting your gun and matching the results to the Chairgun predictions.

I don’t know if I’ve helped you understand ballistic coefficients or if I’ve just confused you more. If you remember the basic things I’ve outlined in this report, it’ll stand you in good stead in your future shooting.


Ballistic coefficient: What is it? Part 1

by Tom Gaylord, a.k.a. B.B. Pelletier

This report addresses:

• Definition of ballistic coefficient (BC).
• How are BCs determined?
• Bullets and pellets have an additional factor.
• BCs are not constants.
• BC is an expression of how much velocity is lost in flight.
• How to cheat the BC numbers.

If ever there was an elephant in a room full of airgunners — this is it! Ballistic coefficient. It seems like everybody talks about it, but what does it mean?

Definition
Ballistic coefficient (BC) is the measure of a ballistic projectile’s ability to overcome air resistance in flight. It’s stated as a decimal fraction smaller than one. When diabolo pellets are discussed, the BCs are very low numbers in the 0.010 to 0.045 range because diabolos are purposely designed to slow down in the air. Their wasp waists, flared skirts and hollow tails all contribute to very high drag that rapidly slows them down — much like a badminton birdie. Lead bullets, in contrast, have BCs between 0.150 and 0.450.

lead bullet comparison
The long lead bullet on the right has a higher BC than the short fat bullet on the left. When they’re both fired at the same speed, the bullet on the right will not slow down as fast as the bullet on the left.

How is it determined?
To physicists, BC is a function of mass, diameter and drag coefficient. This set of parameters seems simple until you examine it closer. A round ball made of pure lead should always weigh the same, as long as the diameter is the same. But a diabolo pellet is conical in shape and can be much longer than the diameter of a round ball of the same caliber. Depending on how the pellet is designed (i.e., how hollow or solid it is), it can also be much heavier because it contains more lead than the ball.

Bullets and pellets have an additional factor
For pellets and bullets, there’s an additional factor to consider — shape. For that reason, there’s a separate definition for the ballistic coefficient of bullets that takes into account the sectional density dictated by the form or shape of the projectile.

I’m purposely avoiding any discussion of BC that includes formulas. Stated simply, a pellet or bullet with a high BC (a large number) will continue to fly much longer than a pellet or bullet with a low BC: A high BC means the pellet will fly farther!

BCs are not constants
Okay, you say, that’s exactly what I want! Give me only those pellets that have high BC numbers.

Not so fast! However, as the velocity of a projectile changes, so does the projectile’s BC. BCs are not constants. There’s no such thing as a pellet with a BC of 0.035. But there are plenty of pellets that will achieve a BC of 0.035 at a certain velocity. When a BC is given, it means something only if the velocity at which that BC was obtained is given with it.

This could get confusing, couldn’t it? Yes, it can be confusing if you try to force numbers onto pellets when they don’t apply. But when you understand that the BC of a pellet is actually a sliding scale, you begin to understand the ballistics of airguns.

BC chart
The ballistic coefficient of a single pellet can change this much with velocity changes.

Who cares?
So what? Who cares about all this sliding scale stuff? You do, and I’ll tell you why. Let’s say there’s a pellet with a BC of 0.042. Wow! That’s a very high number for a diabolo pellet! I’m gonna get me some of them!

Hold on, pardner. What if I told you that pellet was the JSB Exact King in .25 caliber, and that it has that BC only when it’s moving at 1,250 f.p.s.?

BUMMER! You don’t own an air rifle that will propel a .25-caliber JSB exact King up to 1,250 f.p.s. In fact, almost no one does. Therefore, the fact that the pellet has that high a BC at that particular velocity does nobody any good.

If you think about this for a moment, it’ll dawn on you that a particular BC relates to the airgun being used, almost as much as it does to the pellet. Your rifle may only be able to launch the .25-caliber JSB Exact King out the muzzle at 760 f.p.s. At that speed, the BC of the pellet might be 0.033 (these are not the actual numbers, but they’re very close). By the time the pellet has gone 25 yards from the rifle, its velocity has dropped to 635 f.p.s. and the BC is down to 0.030.

BC is an expression of how much velocity a pellet loses in flight
We know that pellets slow down rapidly after leaving the muzzle. Pellets with higher BCs retain their velocities longer than pellets with lower BCs. A pellet with a BC of 0.040 at 900 f.p.s is going to go farther than a pellet with a BC of 0.020 at 900 f.p.s. Both pellets will change their BCs in flight, but the pellet that has the higher BC will never drop below the pellet with the lower BC at the same distance.

Range equals velocity — how to cheat!
I think most shooters know that the velocity of a pellet starts to decrease the moment it leaves the muzzle of the gun. And the BC is a measure of how much velocity a pellet loses in flight. If I want to get higher BCs, I can get them by measuring velocity closer to the muzzle, where the velocity loss will be less than when the pellet has traveled farther. For example, if I were to measure the BC of a pellet by comparing its muzzle velocity to the velocity at 10 meters, the BC would be higher than if I were to compare the muzzle velocity of the same pellet to its velocity at 25 meters.

I can cheat the numbers by measuring velocity loss at a very close range. The pellet that gives me a BC of 0.033 at 25 meters might give me a BC of 0.040 if I measure the velocity loss at just 10 meters. Standards are needed to make sense of these numbers.

Sometimes, people don’t WANT to make sense! Sometimes, people just want to report a high number because the folks reading the numbers think they mean something good.

In that respect, the discussion of BC among those who don’t really understand what it means is not unlike the discussion of muzzle velocity among new airgunners. Some airgun manufacturers proudly advertise their air rifles can achieve 1,300-1,600 f.p.s. People who are new to airgunning think that’s a good thing. We know it isn’t. We know that to achieve such high velocities requires the use of trick pellets no one would ever use in the field because they’re hopelessly inaccurate.

Next time
There’s a whole lot more to this topic. For example, as the velocity of diabolo pellets rises up into the transsonic region, the BC often starts dropping, again. At supersonic speeds, the pellets are very negatively affected.

We’ll also look at the pellet’s shape, for shape is what makes the BC of bullets and pellets different from other BC numbers. Technically, it’s called “form,” but the term shape is clear enough for everyone to understand.


Swaged bullets: Part 2

by Tom Gaylord, a.k.a. B.B. Pelletier

Part 1

This is the second report in this series on swaged bullets. My initial purpose for testing these bullets was to see if I could make a swaged bullet that would shoot more accurately than patched round balls in the rifle barrel of my Nelson Lewis combination gun. While testing that gun, I blew out the nipple and had to repair the gun before it would shoot again. Thankfully, that’s all done now; but I decided, instead, to use a Thompson Center muzzleloader in .32 caliber as the testbed for this idea.

When I first tested the swaged bullets at 50 yards, I couldn’t get a shot on the paper; so this past Monday, I shortened the shooting distance to 25 yards, in hopes I would be on paper. Since I’m reporting this now, you know that I was successful.

One thing I thought might be causing a problem was using too much black powder for the swaged bullets, so I selected a 9mm Luger case as the new powder measure. But there were ignition problems, so that wasn’t the right thing to do. I then adjusted the powder measure back to its smallest measure and shot some patched balls as a control group. The first one was a hangfire that was delayed about 100-200 miliseconds. It sounded like I’d shot a flintlock with a slow lock time. But the second shot with the same load went off perfectly, so I put 4 more downrange after it. This gave a nice group that measured 1.504binches between centers. That’s not great for only 25 yards, but at least the group seemed to be centered on the bull, if a little low.

swaged bullet test 25 yards patched ball
Five patched balls went into 1.504 inches at 25 yards. The 6th shot that landed low was a bad hangfire.

I was exhausting a supply of 3F Goex powder that was at least 30 years old. I’d received it as a gift about 12 years ago, and I think the giver said it was about 20 years old then. So, black powder does hold up over time when properly stored.

One thing I did with the patched bullets was quit cleaning the bore between shots. I used a patch lubricated with saliva, which is recognized as the most accurate round ball lubricant. To do that, I put the patch into my mouth as I began the loading process; then it was wet when I laid it across the muzzle about 30 seconds later. You can only use spit patches if you’re shooting right away; because if the saliva dries, it won’t do anything. Plus, you can rust the bore where it sat. But after 6 rounds had been fired, the bore was still clean enough that I could seat the ball flush with the muzzle with thumb pressure. That told me the bore was not getting any dirtier as the shot count increased. With real black powder, the bore gets dirty on the first shot.

Then it was time for the swaged bullets. The bullets I swaged from .310 lead balls proved too small for success. They missed the target altogether. Then I switched to bullets swaged from .350 lead balls. These seemed perfect and went to the same point of aim as the patched balls. After 4 shots, I thought I had a winner; but shot 5 went almost 6 inches higher, opening the group to 6.25 inches. The first 4 shots measured 1.816 inches between centers — not that much bigger than the patched ball group.

swaged bullet test 25 small bullets with larger bullets
The larger bullet on the left was swaged from a .350 ball. The smaller one came from a .310 ball and didn’t shoot very well.

swaged bullet test 25 yards swaged bullet target1
The swaged bullets did okay until the last shot (upper right). The bore was getting too dirty to shoot well. Notice that at least 2 bullets hit the paper sideways.

This target held a clue to what was happening. Two of the 5 shots appear to have struck the paper sideways, indicating they’re tumbling in flight. Because the bullets are swaged into cylinders rather than spheres, this is very easy to see. Instead of round holes, you get rectangles. Obviously, these bullets aren’t stable in flight, which means they probably aren’t engaging the rifling. Either that or the rifle’s twist rate, which I believe is 1:48″, is too slow.

Some of the holes are perfectly round, however. This either means they were either tumbling and happened to strike the paper point-on, or they were actually stable and for some reason the other bullets weren’t. More work has to be done to sort this out. But let’s now look at the next discovery.

I told you I wasn’t cleaning the bore between shots this time. Well, that came back to bite me. The swaged bullet that had previously slid down the barrel easily was now just entering the bore and staying put. That’s the unmistakable evidence that powder residue is building up on the walls of the bore.

And the next 5 shots on a different target tell the story. Only 4 landed on the target paper and 2 of those went through sideways. The 5th shot landed below the target paper on the paper backer I was using for just this reason.

swaged bullet test 25 yards swaged bullet target2
On the final target, only 4 or 5 bullets hit the target paper. Two of them hit sideways. The 5th shot landed low, off the paper.

That target marked the end of this day at the range. In all, I shot about 25 rounds in about 45 minutes, which is moving right along for a muzzleloader. I tested two weights of swaged bullets with 2 different powder charges and determined that the heavier charge and heavier bullet were both needed. In fact, the next time I test this bullet, I’ll use an even heavier powder charge and try a heavier swaged bullet, to boot.

For the record, I weighed the powder from the measure and discovered it weighed 19.4 grains. This is a light load for a .32-caliber muzzleloader.

I figure the heavier powder charge will help swell the base of the bullet better to grab the rifling, and maybe the heavier bullet will add a little more resistance to help that along. I also plan to clean the bore after each shot, as I now know these swaged bullets require it.

There’s a whole lot more to explore with swaged bullets, but I’ll keep working with this swage set until I know what I’m doing.