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. read more


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. read more



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 read more


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.


Swaged bullets: Part 1

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

This is the start of a long exploration into the use of swaged bullets in both firearms and airguns. I told blog reader Robert of Arcade 2 days ago that I was about to start this one because he was talking about wanting to use the larger smallbore calibers (.22 and .25 calibers) and smaller big bore calibers (.257 and .308) to hunt larger game. But to do that, we need bullets (and pellets) that are accurate.

This report has been nearly one entire year in development, but you’re just hearing about it for the first time today. It all began with my Nelson Lewis combination gun that I have written about many times. Back in the first part of that report, I showed you some original bullet swages that came with the gun. The problem I have with these swages is their design. The bullet is swaged into the die, but then has to be tapped back out of that one-piece die, which is very inconvenient. It would be easier to get out if the die had a separate nose punch that could be taken off the die and the bullet tapped on through.

Nelson Lewis gun swaging dies
These dies came with the Nelson Lewis combination gun I acquired.

Last year at the Roanoke Airgun Expo, I saw that airgunner Mike Reames was making swages for some of his big bore CO2 guns, and people were using them with great success. I talked to Mike at some length about these swages and decided that I wanted to try a swaged bullet in my Nelson Lewis gun. But I conducted a proof of concept test with the rifle — to see if I got the bullet size correct . Unfortunately, I shot what proved to be an overload in the gun. It was a 250-grain .379-caliber bullet, where the weight of the round ball I usually shoot is just 80 grains. The pressure created by the heavy bullet blew the percussion cap nipple off the rifle, and I had to get it repaired. That shut down the experiment for a long time.

Earlier this year, I was at the range with my Thompson Center .32 muzzleloader, and it struck me that I could use this rifle as a testbed for the Nelson Lewis gun. Get the Thompson Center rifle working with swaged bullets, then transfer that experience to the Nelson Lewis gun.

I know the barrel diameter of this rifle quite well, so I again started talking to Mike about a swage set. What I was after was a bullet that would slide over the tops of the lands of the rifling and easily slip into the bore. I reckoned that the force of the exploding black powder would expand the base to both seal it against gas loss and also take the rifling. The bullet I want to make is like a Minie ball that’s swaged instead of cast. If this is of interest to you, email Mike for more info.

What is swaging?
Swaging means to form something in a die by pressure alone. It sounds high-falutin’ but it’s as simple as hammering a nail. And it doesn’t take as much force to swage a small caliber bullet as it does to hammer a small, common 6-penny nail.

My swage set arrived and consists of 4 pieces: nose punch, die body, spacer and swage punch…which works on the other end of the bullet. I asked Mike for a swage to make bullets that measure 0.316 inches on the outside, and the two samples he sent with the swage set measure exactly that size. I was now in business to make swaged bullets!

Bullet swage set
Here are the 4 parts that came with my swage set. From the left, they are the swage die, swage punch, nose punch that goes in the small end of the swage die and the spacer.

bullet swage together
The swage is put together as it is used. I left out the spacer because I don’t use it. I control the swage by controlling the force of the one hammer blow used to make the bullet. The results turn out very uniform that way.

I started by swaging some of the 0.310-inch round balls I’ve been shooting as patched balls in the rifle. The rifle is .32 caliber and the lands are about 0.316 to 0.317 inches apart. The round balls weigh only 45 grains, so the bullet they make is very short. The swage puts a concave hollow into the base of the bullet, which helps the lead base expand when the black powder explodes. The nose is slightly rounded but still has a sharp shoulder to cut a nice hole on paper.

swaging .310 balls
The .310 lead balls in the center were put into the swage die, which was resting on the nose punch. Then, the swage punch was inserted in the die and struck one time. The strike was not as hard as hammering a common nail, yet produced uniform bullets. At the top and bottom, they’re standing up. The right one is laying on its side, and on the left one is standing on its nose to show all parts of the finished bullet. read more


Rifling twist-rate primer: Part 1

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

Recently, we have had a number of questions about rifling twist rates that were attached to the twist-rate report. These questions are extremely important to the understanding of how bullets and pellets are stabilized, so I’m starting a tutorial on rifling twists today. I’ll keep adding sections as I see the need to explain more about the topic.

Today, I want to lay a basic foundation of what the rifling twist rate does. Blog reader Feinwerk asked if centerfire rifles (he said higher-power firearm rifles) had different twist rates than rimfire rifles, and the answer is yes. I’ll get to that, but let me start at a time when things were much simpler.

Early firearms shot multiple projectiles, similar to today’s shotguns that shoot birdshot and buckshot, but much cruder. It wasn’t long before people started experimenting with single projectiles. They found that single projectiles retained more of their initial energy than many smaller projectiles, so they did more damage when they connected with a target. The problem was getting them to connect.

After much experimentation, people discovered that spherical projectiles were the best for firearms. They flew the straightest because they didn’t have the irregular surfaces that created low-pressure zones to guide the bullet astray.

Then, rifling was discovered. Straight rifling (straight lands running parallel to the axis of the bore) was first used as a means of holding all the unburned gunpowder residue, of which there was much. That allowed the gun to be fired more times before cleaning. And, at some point, someone cut the grooves in a spiral — to make them longer to hold even more residue? We’ll never know for sure.

Once people saw how much straighter a spinning ball flew compared to one that was not spun intentionally, the race was on. For hundreds of years, the spinning round ball was the only bullet that was known. It reached its zenith as the patched ball used in the American rifle we know as the Kentucky — where the rifling doesn’t even engrave the lead ball, but spins it by spinning a cloth or leather patch that holds the ball tight while it’s inside the barrel. The ball gets very little distortion from the barrel — although there is a pattern around its circumference where the rifling pressed against the patched ball.

When the patched ball exits the muzzle, the patch falls away and only the bullet travels on to the target. Accuracy increased with this system, and the loading time dropped because the shooter didn’t have to engrave the lead bullet with the rifling when he loaded the bullet/ball.

The conical bullet
Things never stand still, though, and after the patched ball came into general use shooters began experimenting with bullets that were not balls, but rather longer cylinders of lead. These were the first conical bullets.

ball and conical bullet
Although the round ball is very close to the same diameter as the conical bullet, it takes a lot more spin to stabilize the longer, heavier conical bullet.

A ball doesn’t need to spin very fast to be stable because its surface is smooth and regular. A conical bullet, on the other hand, is irregular — being longer than it is wide. Instead of a ball, it’s more like a spinning top that can balance only on its point as long as it spins fast enough. The longer the bullet, the faster it has to spin to remain pointed forward in flight. This attitude is called stability. If the bullet isn’t spun fast enough to remain point-forward, it’ll wobble like a top slowing down; and the varying air pressure that’s created will quickly cause it to tumble in flight. When that happens, the bullet will stray off its straight path.

Twist rate
This is when barrel makers began to be interested in the twist rates of their rifling. Prior to this time, they simply rifled the barrel with whatever twist rate their machinery supported. It’s a fact that the Hawken brothers rifled all their plains rifles with a 1:48″ twist, regardless of what caliber they happened to be.

With conicals, though, the twist rate does matter. Too slow and the bullet tumbles. Too fast and — well, less is known about what happens when the twist rate is too fast; but in my experience, you’re never able to get the same accuracy that you can when the twist rate is just right. A rifle that puts 10 shots into a half-inch with the right twist rate and bullet may put 10 of a different bullet that’s both lighter and shorter (and therefore both moving and spinning faster) into 1.5 inches.

The length of the barrel does not change the twist rate, nor its effect on the bullet — at least not directly. But a longer barrel sometimes does increase velocity. This is always true when black powder is used and can also be true when slower-burning smokeless powders are used.

A bullet that exits the bore of a barrel (of any length) with a 1:12″ twist rate and is traveling 1,200 f.p.s. is spinning at the rate of 1,200 revolutions per second (RPS). Speed that bullet up to 2,400 f.p.s. as it leaves the muzzle, and you increase the bullet’s spin to 2,400 RPS.

If a longer barrel causes an increase in muzzle velocity, it also causes an increase in the rotation rate of the bullet once it leaves the barrel. It does not change the barrel’s twist rate; but because the bullet is going faster; it’s also spinning faster. Reloaders take that into account when they load their cartridges. It’s possible to drive certain bullets too fast or too slow, resulting in less accuracy. Reloading is about finding a balance between the bullet and the velocity at which you launch it.

The M16
The most public and classic case of twist rates and their effects was the launch of the M16 rifle to the U.S. military. It addresses the specific question that Feinwerk asked. The early developers of the 5.56mm cartridge selected a twist rate of 1:14″ because the bullet was barely stable and would tumble and destroy flesh fast when it impacted a body. But they were focused only on the cartridge’s use in Vietnam — a conflict that was mostly conducted at short range and in very warm weather. The 1:14″ twist rate was too slow to stabilize the bullet properly beyond about 250 yards or in very cold weather. It worked great for a 40-grain .224-caliber bullet moving 4,000 f.p.s. from a .220 Swift, but was horrible when used with a 52-grain .224-caliber bullet moving 3,200 f.p.s from an M16.

Don’t confuse the caliber size in inches (.224″) with the name of the cartridge. Both the .220 Swift cartridge and the 5.56mm cartridge (M16) use the same .224″ bullets.

The twist rate for the M16 was increased to 1:12 inches, which worked better, but in time even that rate was discovered to be too slow to do everything the military wanted. Today, the twist rate for an M16 variant rifle runs anywhere from 1:7″ to 1:10″…depending on the specific model of gun, when it was made, which service owns it and what kind of ammunition it’s expected to shoot.

And the answer, Feinwerk, is yes…the twist rate of centerfire rifles does vary by caliber, by the bullets used and the velocities at which they’re driven.

This first twist-rate primer report was written at a very high level. I don’t know whether or not it addresses everything you wanted to know, so I’ll read your comments with interest. If we need to go into greater detail, that’s always possible. Otherwise, I’ll remain at this overview level in the next report.