Archive for July 2013

Scope dope — I hope! Part 3

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

Part 1
Part 2

This series was started for blog reader David Enoch; but after reading the comments many of you have written, I have to think it’s for most of you. Today, we’ll look at optically centering a scope — what’s involved and why you’d want to do it.

What is optical centering?
Optical centering means adjusting the scope until the center of the crosshairs is actually in the center of the field of view. This is difficult to understand; because when you look though a scope, the crosshairs always look like they’re centered. That’s because they’re permanently fixed in the center of a tube called the erector tube. It’s this tube that gets moved when the scope knobs are adjusted.

Not all scopes work this way, I’m aware, but the majority of modern scopes do; so let’s not get into discussions of German scopes and Russian scopes whose reticles actually do move. They’re sufficiently uncommon that there’s no need to confuse the average shooter with their differences.

An optically centered scope is one whose crosshairs remain fixed on a target as the scope is rotated 360 degrees on its axis. I’ve never seen a scope that was perfectly centered, and I doubt one exists. The closest I’ve seen was a scope whose reticle moved about one-eighth inch when rotated 360 degrees while focused on a target 20 yards away. Most scopes can get only to within three-eighths of an inch under those circumstances.

crosshair shift when scope is rotated
When the scope tube is rotated, the intersection of the crosshairs moves against a distant target. The object of optical centering is to get the movement as small as possible.

Why optically center your scope?
This practice started and died with field target. Shooters discovered that if their scopes were not parallel with the axis of the rifle’s bore, not only would the pellet impact rise and fall as the elevation knob was adjusted for different targets — it would also move from one side to the other — typically from right to left, though not always. That’s because the scope was right on at the sight-in distance, but off to one side when the scope was adjusted closer and to the other side when it was adjusted farther.

scope alignment problems This drawing of a top-down view of a scoped air rifle is greatly exaggerated, but it shows how a scope may not be aligned with the axis of the bore.

 

group movement over distance
When the scope isn’t aligned with the bore, this is how the rifle can shoot. You can adjust the vertical reticle for elevation to get all the groups level with the target, but they’ll still land to either side if the scope isn’t aligned.

I was writing The Airgun Letter (1994-2002) when I competed in field target. Although I started out using springers and the holdover method of sighting, I switched to PCPs, which gave me a better chance to compete. I also started adjusting the scope’s elevation for every change in distance. That was when I discovered optical centering.

The way to optically center a scope in those days was to put it on a solid rest that did not move but allowed the scope to rotate around its axis (in this case that means the scope tube) 360 degrees. Then sight at a target at some distance and watch the center of the reticle move against the target.

optical centering fixture
I started with actual machined Vee blocks, until I realized that precision isn’t required to optically center a scope. A cardboard box with 2 Vee notches works just as well.

As you rotated the scope tube, you adjusted both the vertical and horizontal reticles until the center of the crosshairs appeared to move as little as possible against the target. I used graph paper with a quarter-inch grid and a tiny black dot aim point that was about half the size of a pencil eraser.

Adjusting the reticle was not straightforward. If often took longer than an hour to get the reticle moving as little as possible against the aim point. And you never got it perfect. There was always some perceptible movement as the scope tube rotated.

Avoid this trap!
Some people would read about optical centering, then go to the range with thoughts of performing it at twice the distance to get even greater precision. It never worked because at 40 yards you can’t see the movement of the crosshairs shifting by one-sixteenth of an inch against a target.

Others were simply never satisfied with the results they got from optical centering. They knew their scopes were not perfect, and they couldn’t live with that. So, they kept swapping scopes and returning to the range again and again, searching in vain for the scope whose crosshairs could be adjusted to remain centered when the tube was rotated.

In the end, those who’d been proponents of optical centering realized they were chasing their tails. Perfection was impossible and there were other easier things that could be done that would deliver the same results. Mounting the scope in line with the bore is just as successful as optically centering it.

Why did optical centering die?
Many shooters are still not aware that they don’t need to optically center their scopes, so it hasn’t really died…but most field target competitors — at least the ones that win — don’t do it anymore. Instead, they take great pains to align the scope with the axis of the bore so centering becomes a non-issue.

If your scope is not optically centered but the scope is aligned, you can correct any misalignment of the reticle during the sight-in. You aren’t fighting the angles of the line of sight and axis of the bore. So, extra time spent mounting the scope pays off in not needing to go through this cumbersome procedure. The results are the same either way. As you adjust the vertical reticle, the shot group remains centered at all practical distances.

Big Shot of the Month
Pyramyd Air’s Big Shot of the Month on Facebook is Roberto Martinez. He’ll receive a $100 gift card. Congratulations!

Pyramyd Air Big Shot of the Month

Roberto Martinez is the Big Shot of the Month on Pyramyd Air’s airgun facebook page.

Why powerful mainsprings don’t always increase velocity

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

Today’s report is the one I mentioned forgetting in last Friday’s blog! Blog reader Errol reminded me about it yesterday.

I hear this so often from airgunners — how they think they’re going to add a more powerful mainspring to their airguns and increase the power. It sounds logical, but it often doesn’t work; and it nearly always doesn’t work as well as you think it should. Today, I want to discuss why that is.

Fact 1
The Weihrauch HW 35 was always considered to be one of the most powerful airguns in its day — which was the 1950s. They delivered over 700 f.p.s. when new in the 1950s; and over time, this rose to 750 f.p.s. Careful tuning could get close to 800 f.p.s. from certain guns. This model is still being made today, but now it sells because it’s so pleasant to shoot and doesn’t produce excessive power. How times change!

The HW 35 was so-named because the length of the piston stroke is 35mm. Piston stroke is the distance the piston travels from being cocked to being at rest at the end of the firing stroke. When Robert Beeman set out to make what eventually became the Beeman R1 rifle, he used the HW 35 as the starting point and increased the piston stroke to 80mm. And that’s where the additional power comes from — the piston stroke length and not the strength of the mainspring. Greater stroke length means greater swept volume, which means more air to compress for the shot. It doesn’t matter all that much how fast the air is compressed, which is the only thing a stronger mainspring does.

Fact 2
Then, there’s the story of the man who wanted to build a supersonic .22 pellet rifle. So he took the Beeman R1 as a starting point and built one that was 125 percent larger. The late Steve Vissage built a Frankenstein rifle that I documented in a report called Steel Dreams. It weighed 11 lbs., took 53 lbs. of force to cock and was larger than the R1 in every way, save one. It developed the same power! Yes, bigger mainspring and wider piston did not increase the power of the gun one iota.

Why is this true?
I know you want an explanation of why a more powerful mainspring doesn’t necessarily increase power. Here it comes:

THE MAINSPRING DOESN’T ACT DIRECTLY ON THE PELLET

The mainspring pushes the piston. The piston compresses air in front of it, and it’s that compressed air that gets behind the pellet and pushes it up to speed. The mainspring never touches the pellet. So, changing the mainspring has no direct effect on the speed of the pellet.

Here’s a good example everyone will understand. We have a house with a hollow-core door as the front door. Forget the fact that it violates all building codes — your cheap Uncle Rufus put it on when the old front door finally broke. This one was dirt cheap, which is why he got it. But your Aunt Thelma is justifiably worried about a break-in; so when Rufus is out of town, Thelma has a locksmith install a super-duper triple deadbolt lock on the door. Is that going to protect her? Of course not. Any burglar can simply break the door apart with one good kick. The lock will still be secure, but there won’t be any door attached to it.

Do any heavy mainsprings ever work?
Am I saying that heavier mainsprings never work? No, I’m not. When I was testing the Beeman R1 for my book, I installed the Mag 80 Laza Kit from Venom in England. Ivan Hancock created a drop-in kit of parts that worked well in the R1/HW 80 and increased the power. The mainspring was a very long stiff spring with thicker wire, and it was coated with a black tarry substance that I named black tar in my newsletter articles. That’s where the term black tar comes from. Black tar is also called velocity tar in some circles.

The R1 went from requiring 36 lbs. of force to cock to 50 lbs. with this kit. But the heavy mainspring was not directly responsible for the power increase. The kit also included a new piston that had 6 synthetic bearings that are now called buttons. These buttons rode against the spring cylinder walls and kept the steel piston from touching the steel spring cylinder.

Here’s the deal. The new piston was harder to slide inside the spring tube because the synthetic bearings pressed tightly against the sides of the spring tube. The powerful mainspring simply brought the piston’s speed back to parity with the factory piston. What increased the power was a combination of a better piston seal and the elimination of all piston vibration when the gun fired. The gain was just a few foot-pounds of energy, but the rifle was now getting everything the R1 design could possibly give.

A parallel in the pneumatic world
Most of you readers are aware that pneumatics work within pressure limits, and over-pressurizing them doesn’t add power — it takes it away. The reasons are different, but the end result is the same as for heavier mainsprings. The design of the gun is being overcome by one thing (the mainspring in a spring gun, or too much reservoir pressure in a pneumatic) and the performance balance is tipped toward the negative.

CAN a heavier mainspring increase the power of a springer?
Yes, it can if you also change the rest of the powerplant along with the mainspring. And no, it won’t if a heavier mainspring is all you add. The secret to more power is to balance all the components so the gun performs at its optimum. With all airguns, there’s a limit to how far you can go. Where that limit is depends on the rest of the design — the parts that are too expensive to change.

You can break your heart trying to buff up a dirt clod to a high shine. Or you can start with a gun that has some potential and make real progress by artfully changing the things that matter. The secret is to know which is which.

One last remark
Pyramyd Air is stocking the most recent issue of Airgun Hobbyist magazine. If you want to try just a single issue to see if a subscription is worthwhile, now’s your chance.

Crosman M1 Carbine BB gun: Part 1

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

Crosman M1 Carbine and U.S. Carbine
M1 Carbine on top and Crosman M1 Carbine below. A realistic copy!

When I attended San Jose State College in the 1960s, I was in ROTC. My first 3 years as a cadet were in the enlisted ranks, and we all drilled with the M1 Garand. Today, people feel the Garand is a cool historical military weapon (and it is!); but in the late 1960s when it was all we had, it wasn’t nearly so cool. It was, in fact, heavy, clumsy and dangerous when you performed Inspection Arms. We learned to live with it and eventually became adept at not smashing our thumbs when we closed the bolt, but the fact was that the Garand was a 10.5-lb. clunk that always seemed to weigh too much.

The cadet officers, in sharp contrast, were issued the M1 Carbine, which weighed about half as much and felt like a feather compared to the Garand. When they performed Inspection Arms, there was no heavy spring to fight to get the bolt open and no chance of an M1 thumb. The bolt on the Carbine action slides home with minimal fuss.

Of course, we never got to shoot our guns. We just drilled with them. I could perform the Manual of Arms pretty well but had no idea what it was like to touch off a round. And those days were long before Garands became widely distributed among private owners in the U.S. They were around, but a kid in college like me shot a 1903 Springfield if he shot anything.

Carbines were more readily available, but I never had the chance to shoot one of them, either. So my entire opinion of both weapons was based solely on their weight and the relative ease with which the Manual of Arms was performed. Naturally, I fell in love with the M1 Carbine.

I wasn’t an airgunner in those days. I’d been one 10 years earlier when firearms were out of the question…and I would be, again, in a few years when I encountered adult airguns during a tour with the First Armored Division in Germany. I was unaware that Crosman had marketed an M1 Carbine lookalike BB gun from 1966 to 1976. And, given my interest in firearms at the time, it’s doubtful that I would have been interested in one if I had known about them.

It wasn’t until I started going to airgun shows in 1993 that the Crosman M1 Carbine popped up on my radar screen; and when it did, I assumed it was a CO2 gun since my total knowledge of Crosman was that they made CO2 guns. Having lived through the great experiment of the “bottle-capped” CO2 containers in the late 1950s (they leaked gas), I wanted nothing to do with any gun that used it. That’s a story of its own, and it’s one I’ll share with you soon.

Bottle cap CO2 cartridge
Crosman’s first CO2 cartridge (right) used a type of bottle-cap close. Many leaked.

In the late 1980s, someone offered me a Crosman M1 Carbine for $15, and I turned it down because of my distaste for CO2 guns. It wasn’t until about 10 years later when I was writing The Airgun Letter that I discovered my mistake. The Crosman M1 Carbine is not a CO2 gun. It’s a spring-piston BB gun that cocks using the push-barrel system that Quackenbush (Henry Marcus, not Dennis) made popular in the late 1800s.

I also discovered that this BB gun had a rear sight that adjusts in the same way the type II and type III Carbine rear sights adjust. And it’s lightweight — just like the military gun. And powerful for a BB gun! And also accurate. What was not to like?

Crosman M1 Carbine rear sight
The Crosman rear sight is fully adjustable for windage and elevation — just like the type III military Carbine rear sight.

M1 Carbine rear sight
A military Carbine type II rear sight is very similar to the Crosman sight. They adjust the same way!

I broke down and bought a wood-stocked Crosman M1 Carbine at the Winston-Salem Airgun Expo. That gun taught me what I’d been missing all those years. It was accurate (for a BB gun), powerful and looked great. But those were busy days when I was buying and selling airguns often to have new material for the newsletter. So, I let that gun get away from me — for almost twice what I paid to get it! That was the value of the wood stock, which was available only for the first two years of production.

Then I went into a severe case of seller’s remorse, which I guess I also verbalized a little. My friend, Mac, saw me looking at another M1 Carbine at another airgun show, and he bought it for me as a gift. That was the kind of friend he was.

Following that, I got serious and set about to acquire my first actual M1 Carbine firearm — just to complete the circuit. I found it to be wimpy, weak, inaccurate and in all other respects thoroughly lovable. I have not been without a Carbine since. And I will never get rid of my Crosman M1 BB Carbine.

The rifle
The Crosman M1 Carbine is a very realistic airgun. It weighs 5.25 lbs., which is within 1 ounce of the firearm’s weight. The stock is plastic dyed medium brown and given a grained pattern on the surface. Crosman called it Croswood, and for its day it was very realistic. In fact, it looks much more authentic than the real wooden stock that’s slab-sided and without figure. The Croswood stock is much more rounded and more fully contoured than the wood stock.

The picture shows that the airgun is in most ways very similar to the firearm. Of course, there are some significant differences. The “magazine” for instance is nothing but a metal box — a reservoir for BBs that must be dumped out and then loaded into the 23-shot gravity-fed magazine before they’ll work in the gun.

Crosman M1 Carbine magazine out
Crosman’s magazine is really just a reservoir for extra BBs. They have to be removed from the reservoir and loaded into the gun.

Crosman M1 Carbine magazine opened
Slide the plastic cover off the magazine and pour out the BBs.

That magazine, by the way, is the gun’s Achilles heel. Kids (and parents who don’t understand its purpose) remove it and lose it. The gun will still work fine without it, but some of the authenticity is lost. There have been solid plastic magazines sold over the years for those who need to regain the look without the storage compartment.

The BB gun loads through a hole in the top of the stock. To load, you slide the operating handle to the rear to open the hole, then drop in the BBs one by one. They roll back toward the butt, which is natural. When you cock the gun, you pull back on the barrel and normally the muzzle will be elevated when you do.

This gun can be difficult to cock — even for some adults. The mainspring is powerful, and the barrel doesn’t offer a good handle to grasp when pulling it back. Many people cheat by putting their palms over the muzzle and pushing the barrel back. That puts your palm over the muzzle of a cocked gun — which is not something you want to do.

The right way to cock the gun is to use the front sight as an anchor for your index finger but not put any part of your hand in front of the muzzle at any time. I’m sure kids developed their own ways of cocking this gun, as it’s entirely too powerful for most youngsters to cock conventionally. Most Carbine BB guns will have significant finish wear on the barrel just behind the front sight due to repeated handling.

Crosman M1 Carbine grasping barrel to cock
Grasp the barrel this way to avoid putting your hand over the muzzle. This wears the finish off the barrel at this point.

The pull of the stock is a somewhat short 13 inches. But the firearm’s pull extends only another quarter inch farther, so it’s right in line with that. And the overall length is 35.50 inches for the BB gun and 35.75 inches for the firearm. So, the pull is where the difference is.

This gun was an icon to kids growing up in the late ’60s and ’70s. It was (and still is) so realistic that every junior BB-gunner wanted one for himself. Even if he couldn’t cock it without resorting to trickery, this was a gun to own!

Range tools

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

Today’s report is a placeholder for one I promised earlier this week and forgot what it was. If you were looking for a particular report today and didn’t get it, please tell me what it is and I will reschedule it.

I was at the range yesterday, shooting off my rifle rest, when I discovered the rest was wobbling. That’s not good because one of the most important things a rest should be is stable. Normally, I would have been unable to fix the problem, which was loose bolts on the rest; but every tool I needed to make the repairs was in my range bag. So, I thought we could take a look at what I carry with me to the range. What you are about to read comes from years of shooting and thousands of hours on the range, where you sometimes need a tool.

Job No. 1
As things turned out, I needed special tools for 3 different jobs this day, and I had all of them in my range box. So let’s take a look. The first job was to tighten that rifle rest.

multi-tools
These three multi-tools and the small tool set have saved the day many times!

The rifle rest had bolts that were too hard for the pliers on my multi-tools to turn. But I also carry 2 small crescent wrenches, and one was the right size for the nuts on the end of the bolts. The bolt heads have large Allen wrench sockets, but I don’t carry an Allen wrench set with me. However, in a small tool set I do carry I found the exact size Allen wrench bit that was needed, so the bolts were tightened and the rest became rigid again.

crescent wrenches
I carry not 1 but 2 crescent wrenches because sometimes you need both. The duct tape has many uses and the plumber’s tape is for sealing pneumatics and CO2 guns. The shorter wrench is one I cut down years ago to carry on my bicycle.

Job No. 2
Then my shooting buddy, Otho, tried to sight-in his new Ruger .44 Magnum Deerslayer carbine. Turned out he needed a very tiny screwdriver bit for the rear sight’s elevation, and the small toolkit I carry happened to have exactly the right size! The ironic thing is that Otho gave me this set about a year ago!

We also had to drift (push sideways in a dovetail slot) the rear sight to get it aligned correctly, and one of my multi-tools has a small claw hammer that was perfect for the job. Otho had a brass drift punch, but the hammer he had was too small to move the sight. After getting the rifle sighted in, I put 8 out of 10 shots on a 6-inch bullseye at 100 yards, so the job was a complete success.

Targets
I always carry a wide variety of paper targets to the range because I never know exactly what I’ll need. I have 5-10 of each of these, plus targets not shown. The squares are great for 100 and 200 yards with powerful scopes!

Stapler
You always need a stapler for the targets. And don’t forget to carry staples. I reload the stapler as soon as I hit the range and usually don’t need staples for the rest of the day.

Job No. 3
Then, we went to the 15-yard range, and Otho’s wife tried out a .32 S&W double-action revolver as a possible defense weapon. Otho had loaded the cartridges a long time ago, and they were very low power. So low, in fact, that they had ignition problems and one turned out to be a squib. The bullet was stuck in the barrel.

I always carry a .177-caliber cleaning rod to help extract rifle cartridges from guns with bad extractors. I’ve used it dozens of times just this year. But a .177 rod is too thin to drive a stuck lead bullet out of a barrel, so I also carry a military .30-caliber cleaning rod that’s broken down into many sections. One of them was perfect to drive the .32 bullet out the barrel so the gun could continue to shoot.

Cleaning rods
The .177 cleaning rod in the package has been used many times to push fired cartridges out of the chambers of rifles. The heavier .30-caliber jointed rod at the bottom is strong enough for many tougher jobs.

Then there are the supplies that I always need away from the house. For pneumatics, I carry a small jar of diver’s silicone grease to lubricate the o-rings on fill connections at the range. I also carry a couple CO2 cartridges in case I’m testing a CO2 gun and run out.

CO2 cartridges and diver's silicone
I carry diver’s silicone grease for pneumatics and CO2 cartridges just in case I run out. The gel pad was a Pyramyd Air giveaway several years back. I use it sometimes to rest my elbows when shooting off a rest.

Finally, there’s safety to consider. I always have several sets of disposable earplugs, and lately I’ve had to give them out. People go to a rifle range and forget to bring hearing protection. It’s such a common problem that they sell packages of a dozen plugs just for range bags. The binoculars are not in place of a spotting scope, but to augment one. If the caliber is large enough or the target is close enough, I don’t go to the trouble of setting up a spotting scope.

earplugs and binoculars
Earplugs are always with me, as are the binoculars. As cheap as optics are, today, I have several pairs in key locations. The yellow tool is a combination set of Allen wrenches and screwdriver bits. It isn’t that useful, but I have used it occasionally.

Other useful tools
That’s a quick look inside my range bag. I didn’t show some of the oils and solvents, but these are the big things I carry. What do you carry?

Evanix Rainstorm 3D bullpup: Part 2

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

Part 1

Evanix Rainstorm 3D Bullpup
Evanix Rainstorm 3D bullpup

Well, the opinions of this rifle are sharply divided. People either love it or hate it, and nothing in between. A few haven’t made up their minds yet; but when they do, it’ll be one extreme or the other. The Evanix Rainstorm 3D bullpup is as far from a Diana model 27 as an air rifle can get.

Blog reader Rob is the only owner who has commented, thus far, and he says he loves his .25-caliber bullpup. He reports getting 25 good shots per fill and wants one in .177 for the greater shot count and 9mm for the additional power.

Some things I missed last time
I forgot to mention that there’s also a Picatinny rail under the forward part of the gun. This would be for a laser, flashlight or bipod.

I also failed to mention that the trigger is adjustable for both first- and second-stage pull. The second-stage adjustment is a sear contact adjustment, so you must be careful not to go too far or the gun will either become unsafe or won’t cock at all. After I see how the trigger is out of the box, I may attempt some adjustments.

Assumptions
Many of you took my comments too seriously last time. I mentioned that bullpup designs are notorious for poor triggers, and you assumed that this rifle’s trigger is bad. I haven’t tested it yet. It may be fine. We won’t know until I have the chance to shoot the gun.

And some of you criticized the gun for not having open sights. That’s like criticizing a Dodge Viper for not having a trailer hitch! The design of a bullpup doesn’t lend itself to the use of open sights. I don’t know of any bullpup firearms that have open sights, either. Compasseco used to sell a sidelever spring rifle bullpup that had open sights; but when you saw how high they had to be to be seen by the shooter, you understood why optical sights were preferred.

The magazine
The magazine is loaded through the larger hole on the left at the back. The back is the side where you can see 2 holes, while there’s only one hole visible at the front. The pellets do not drop into their holes. The have to be pushed in with something like a ballpoint pen. Once in, rotate the magazine one click counterclockwise and load again. Keep doing it until all 11 pellets are loaded.

Evanix Rainstorm 3D bullpup magazine
Load through the larger hole on the left. The pellets will not enter the magazine without a push from a ballpoint pen.

Velocity testing
Looking at the published velocity of the .22-caliber rifle I’m testing (1,176 f.p.s.), I decided that the gun wants to shoot heavy pellets. With all that power potential, this is potentially a 50 foot-pound air rifle, according to those numbers. The first pellet I loaded was the JSB Exact Jumbo Heavy pellet, which weighs 18.1 grains in .22 caliber.

Evanix Rainstorm 3D bullpup pressure gauge
This is what the on-board pressure gauge reads when the gun has 2,900 psi inside.

The gun does not have a flat power curve. It drops in velocity from the first shot to the last, similar to many other Korean-made magnum PCPs I’ve seen. The shot count is simply how far down you’re willing to allow the velocity to drop. The next numbers for the JSB Exact Jumbo Heavys should explain everything.

Shot     Vel.
1……….1045
2……….1033
3……….1020
4……….1022
5……….1006
6……….1008
7…………997
8…………991
9…………981
10………..971

Average (shots 1-10) 1007 f.p.s.; energy — 40.72 foot pounds

Shot     Vel.
11……….959
12……….948
13……….939
14……….926
15……….915
16……….910
17……….898
18……….892
19……….882
20……….874

Average (shots 11-20) 914 f.p.s.; energy — 33.58 foot-pounds

Shot     Vel.
21……… –
22……….867

After seeing the first string of 10 shots, I normally wouldn’t go any farther; but I know several of you may be curious to see if the gun ever settles down and delivers several shots of similar velocity. As you can see, it never does. After this string of shots, the pressure in the reservoir was 1,400 psi, so the gun was shot out. I call that 10 shots per fill.

If the valve were tuned to deliver about 30 foot-pounds, there would probably be a group of 20 shots or so that were similar in velocity. As the rifle is now, it is running flat out, as fast as it can from start to finish.

Beeman Ram Jets
Next, I tried the obsolete Beeman Ram Jet pellets. They weigh 16.5 grains and combine the dome and wadcutter shapes. After a fresh fill, they averaged 1026 f.p.s. for the first 10 and they ranged from a low of 997 f.p.s. to a high of 1051 f.p.s. As with the first pellets, the velocity fell straight from the first shot. At the average velocity, this pellet averaged 38.58 foot-pounds.

Eun Jin domes
The last pellet I tried was the 28.4-grain Eun Jin dome. I tried it for two reasons. First, I wanted to see if they would feed in the magazine. They fed perfectly, so this is a pellet you can shoot in this rifle — at least in .22 caliber. Second, since this was the heaviest pellet I could get through the magazine, I wanted to see what kind of energy it might develop.

Eun Jins averaged 877 f.p.s. for 10 shots on a fresh fill. The low was 844 f.p.s. and the high was 907 f.p.s. At the average velocity, this pellet generates 48.51 foot-pounds of energy at the muzzle.

Trigger
The trigger changed behavior, once the rifle was cocked. It became as stiff and creepy as the bullpup reputation has caused us to expect. However — and this is very significant — I adjusted stage two by the owner’s manual, and the pull became crisp and the letoff dropped to 6 lbs., 10 oz. This was as low as it would go and stay cocked because of the direct sear adjustment. There just wasn’t anymore contact area to play with after I finished adjusting it.

So far, so good. It’s obvious from these figures that this rifle is meant to be a hunting air rifle — pure and simple. Oh, and the discharge sound is a very loud number 5 on the Pyramyd Air sound scale.

How does rifling twist rate affect velocity and/or accuracy? Part 13

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

Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
Part 7
Part 8
Part 9
Part 10
Part 11
Part 12

This is the summary report in this series. I’ll give you my thoughts on how this test went, and I expect you to comment, as well.

The barrels
Three barrels were used in this test. One was the factory barrel that comes with the .22-caliber AirForce Talon SS. It’s a 12-inch Lothar Walther barrel that has a choke of about a half-thousandth inch reduction in the bore diameter for the final 2 inches of length. That makes all the pellets of uniform size as they leave the muzzle, and it may potentially stop any in-bore wobble. This barrel has the standard airgun twist rate of 1-turn-in-16-inches of bore travel, written as 1:16″.

The other 2 barrels were made by Dennis Quackenbush. Neither barrel is choked. One is a 1:12″ twist; the other is a 1:22″ twist. They’re also about 12-inches long and are held in the gun by AirForce Talon SS barrel bushings. Several comments have suggested that because these barrels are different than the Lothar Walther barrel, this test is somehow not fair. But the results of all the shooting prove otherwise. Sure, there are variations from barrel to barrel, depending on the power used and which pellet was shot. But the results are so close between all 3 barrels that whatever differences there might be are overridden by the similarities. In other words, I’m suggesting that if Lothar Walther had made all 3 barrels, there would be similar differences.

Talon SS precharged air rifle twist rate test 3 barrels
The 3 barrels used in the test. Factory barrel in the middle.

I believe the twist rates are what drive the results. We weren’t searching for the most accurate barrel in this test. We were looking for behavior changes as conditions were changed. And we got that.

Velocity
The first thing that was tested was velocity. Both pellets — the 14.3-grain Crosman Premiers and the 15.9-grain JSB Exact Jumbo were shot from all 3 barrels at each of 3 predetermined power settings. These settings were marked on the gun so they were kept constant throughout the test.

Talon SS power settings
The power settings were the power indicator screw all the way to the left (the lowest setting), and the power screw centered on each mark (settings 6 and 10).

 

07-24-13-01-Velocity-table

I reviewed the velocity for you in Part 8. Here’s a summary of that report.

In all cases, the velocity increased the most between power setting zero and setting 6. The velocity increase from setting 6 to setting 10 was always smaller than the increase from setting zero to setting 6, and that’s irrespective of the twist rate or which pellet was shot.

What you’re seeing here is the slowing down of the rate of velocity increase as the air flow increases. That’ll become clear in a moment when I discuss the rifle’s maximum velocity potential.

As the twist rate slowed (1:22″ is slower than 1:12″), the velocity increased at most power settings with most pellets. There was one instance with the 1:22″ barrel when the JSB Exact pellet actually went 2 f.p.s. slower at setting 10 than at setting 6; but with all other barrels and pellets, there was always a velocity increase as the power setting went higher.

Focusing on the 1:22″ barrel for a moment, we see that the velocity increases between setting 6 and setting 10 were not as great as they were in either the factory (1:16″) barrel or the 1:12″ barrel. This suggests what we have suspected all along — that the twist rate of the barrel does slow down the pellet as it gets tighter. And we can see from this test that the phenomenon is most apparent at the lower power settings. At the higher power settings, the differences seem to shrink, indicating that the influence of the power setting is overriding the influence of the twist rate. I believe this is an important finding, and it sets up the next observation, which is that the top velocity of the gun was fairly close for all 3 barrels, regardless of the twist rate. The type of pellet made more difference to the top velocity than the barrel twist rate did.

It should be obvious from these results that the Talon SS powerplant has upper limits that cannot be exceeded by forcing more compressed air through the barrel. This illustrates the relationship between barrel length and velocity in a pneumatic airgun.

A second thing I found interesting is that power setting 6 is very close in performance to power setting 10. In the case of the 1:22″ twist barrel, it’s remarkably close…but it’s close for all three barrels. A prudent airgunner might consider this when setting the power wheel adjustment on his Talon SS, knowing that a lower setting uses less air, yet gives velocity that isn’t that much slower.

A third thing is that the velocity performance of the 1:22″ barrel is so good at power setting 6 that it makes power setting 10 useless. Take that thought just a little farther, and you’ll see that all power settings above setting 10 are pretty much a waste of air in a Talon SS with a 12-inch barrel, regardless of which pellet you use.

Accuracy testing
Next, I tested all 3 barrels with both pellets shot at all 3 power levels at 10 meters (11 yards) and 25 yards. Following that, I tested all 3 barrels and both pellets, again, at 50 yards, only I didn’t use the zero power setting. This was where my eyes were opened regarding the effects of twist rate.

Accuracy table final

I analyzed the accuracy in 2 different reports. One (Part 9) was the 10-meter and 25-yard accuracy and the other (Part 12) was the 50-yard accuracy, alone. Now, with the table above we can combine these results and analyze all the accuracy data together.

The first observation I’ll make is that at 10 meters, I got 10-shot groups that ranged from as small as 0.092 inches to as large as 0.578 inches. The factory barrel gave the best results with the JSB pellet; but with the Premier, it was the 1:22-inch twist that did the best. Curiously, that pellet and twist rate didn’t seem to change that much as the power was increased (at 10 meters). With all other barrels and pellets, the group size did change a lot as the power changed.

It’s too simple to say the factory barrel with the 1:16-inch twist rate is the best; but of the 3 twist rates in this test, it certainly is the most flexible across the board. However, you’ll notice that the 1:12-inch twist barrel did shoot the best single group (with JSB Exact pellets) at 50 yards. That group is so close to the Crosman Premier group shot by the 1:16-inch barrel that I can’t call a clear winner — BUT — here is what I CAN say. The Quackenbush 1:12-inch twist barrel is certainly capable of shooting 50-yard groups at least as tight as those shot by the Lother Walther barrel; and in my mind, that puts the barrel-equivalency question to rest.

Another observation is that the 1:22-inch twist barrel was just as good at 10 meters as the other 2 barrels, in general, but look at how the groups opened at 50 yards! That says something very strong about the relationship of the twist rate to accuracy. And it also brings up a second observation.

Premier pellets and JSB pellets performed differently throughout this test. Just look at the 50-yard results for Premiers and JSBs with the 1:12-inch twist barrel, and you’ll see what I mean. This is one more bit of evidence that barrels have preferences for certain pellets.

Final observation
This will be my final remark in this series of reports, and it does not come from the data collected in this test but from the 5-part test of the Diana model 25 smoothbore. In that test, we saw that the smoothbore was able to place 10 JSB Exact RS pellets into a group measuring 0.337 inches at 10 meters. However, at 25 yards, the same pellet loaded the same way made a group that measured 3.168 inches. That difference tells us clearly that spin and not aerodynamic drag is the main key to pellet accuracy. I think we now see that twist rates do matter a lot, and the standard rate is the best all-around rate for now.

Diana 25 smoothbore JSB Exact RS deep-seated group
At 10 meters, 10 JSB Exact RS pellets made this 0.337-inch group.

Diana 25 smoothbore JSB Exact RS deep-seated group2 25 yards
At 25 yards, the same JWB-Exact-RS pellets, seated to the same depth, made this 3.168-inch group. They are clearly not accurate after 10 meters.

UTG Bug Buster 3-9X32 AO rifle scope: Part 1

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

UTG Bug Buster 3-9X32 right
The 3-9x Bug Buster packs a lot of performance into a small package.

UTG Bug Buster 3-9X32 left
Bug Buster left side.

Today, we’ll start looking at Leapers’ new 3-9X32 UTG Bug Buster rifle scope. As you know from yesterday’s blog, I’ve mounted this scope on the Evanix Rainstorm 3D Bullpup for testing. I feel the small scope compliments the compact size of the bullpup.

UTG Bug Buster 3-9X32 on Rainstorm
The Bug Buster looks good on the Rainstorm 3D bullpup.

Boy, has Leapers come a long way with the Bug Buster since it first came out! First of all, let’s get the introductions out of the way. Leapers is the manufacturer. UTG, short for Under The Gun, is one of their product lines. Bug Buster is a name that airgunners gave to this scope when it first came out. Because it held (and still holds) the world record for close parallax adjustment, which in practical terms is the same as focusing, the compact scope was touted for shooting insects as soon as it hit the market. Someone coined the name Bug Buster, and Leapers adopted it as their own.

That first Bug Buster was a fixed 4x scope. Today, I’m testing a 3-9x variable. What a difference that makes. Not only can you focus as close as 9 feet, you can also magnify your target 9 times at that distance! If you’re sighted-in, you can pick which part of the bug to eliminate.

UTG Bug Buster 3-9X32 3 yards
This is something no other scope in the world offers — parallax correction down to 3 yards!

But there’s a whole lot more than just close focusing. This Bug Buster comes with lockable turrets, which are the adjustment knobs for windage and elevation. To lock or unlock them, a ring at the bottom is loosened or tightened. Do it once and it will seem intuitive.

The zero can also be reset; so once the scope is zeroed for a certain range, the scale can be repositioned so it reads zero. This allows you to adjust the scope from this zero and see how far you’ve gone — as long as you don’t go farther than one full rotation of the adjustment knob. It’s very handy for hunters who wish to change their scope zero in the field.

The reticle
The big reason I’m testing this scope is the reticle. Early Bug Busters had one shortcoming — a thick reticle. Precision aiming was difficult , if not impossible, because the crosshairs covered so many inches at 100 yards. That’s what’s changed in the new Bug Buster. The reticle is a mil-dot. The reticle lines are now about medium-sized. They won’t cover too much of your target, and yet you can still find them while hunting in a dark forest that has lots of shadows.

There are dots on the inner lines in both directions. The centers of the dots are one mil apart, which provides a refernce for measuring angles through the scope. And angles can be turned into distances if you know the approximate size of what you’re measuring.

In the Army, we had to learn the approximate size of common battlefield equipment such as tanks and personnel carriers so we could calculate the distance to them with binoculars that had a mil-scale reticle. Hunters need to learn the same sorts of things, but for the animals they’re likely to spot. That information, coupled with the tutorial in the scope’s owner’s manual, will help you calculate distances to your target.

The reticle is illuminated with Leapers’ patented EZ-TAP lighting system. Two buttons atop the scope control the intensity and selection of the colors. Now, I’m colorblind, as are up to 14 percent of all males. My malady is a red-green defiency, which is the most common type. That doesn’t mean I can’t see those colors — I just don’t see them the way a person with normal sight sees them. So, the question is: How valuable is it to me that there are 6 different colors for the reticle and 6 levels of intensity for each color? Well, as a matter of fact, I can differentiate each of the 6 colors when they’re at their most intense. But when the intensity level drops, most of the colors become gray to my eyes. I can see them, but they don’t seem to have much color. The red and the green colors stand apart as the most vivid of all.

UTG Bug Buster 3-9X32 EZ Tap
Those two buttons control the colors and intensity of the illuminated reticle. There are 36 choices available.

I will say that you need to read the manual to fully understand how to operate this scope. Not only does it address the EZ-TAP operation, it also goes into great detail on how to estimate range with the mil-dots.

But wait — there’s more!
As if all those features weren’t enough, this scope comes bundled with UTG Max-Strength, quick-detach, medium-height rings. These sell separately for $25, and my friend Mac reviewed them for us in 2011. Mac reviewed 30mm rings and these are one inch, but in all other aspects they’re identical.

UTG Max Strength Quick Lock Rings
A set of UTG Max-Strength, medium-height, quick-detach rings comes with the Bug Buster.

Packaging
If you’re a store owner, the UTG scope line now comes in glass-clear packaging that allows the customer to see the scope inside. I call it the Snow White box. This packaging is sealed at the factory, so a customer will know if it’s been opened before he receives the scope…because there’s clear film tape that must be removed to get inside the box. That should end the claims of selling used merchandise, which is pretty common in the scope world.

UTG Bug Buster 3-9X32 package
The new UTG packaging is transparent, so everyone can see what’s inside. Clear protective film/tape keeps them out until the scope is sold. Obviously, this doesn’t show the scope from today’s blog, but it demonstrates my point just the same.

Dimensions
The Bug Buster is a compact scope. It’s just 8.5 inches long and weighs only 13.9 ounces. The tube is one inch in diameter. It’ll look petite on most normal air rifles and just right on the small ones. The only consideration the size brings is the scope tube sections are very short on either side of the turret, so the rings don’t have much room to move. If your rifle has a built-in scope stop, this scope may not come back far enough for the proper eye relief. On guns like the 3D bullpup and big bores with short receivers though, the Bug Buster might be the best scope out there.

Testing
The only way to test this scope is by firing the gun and adjusting the reticle. So that testing will have to wait. I can tell you now that the optics are clear and sharp, and the eyepiece has buckets of corrective adjustment in it. The rest will await the testing of the Rainstorm 3D bullpup.

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