How does rifling twist rate affect velocity and/or accuracy? Part 5
by Tom Gaylord, a.k.a. B.B. Pelletier
If you’ve reached this webpage because you’re searching for information about the AirForce Talon SS rifle in .22 caliber, please note, this report is not about a standard rifle. You may be more interested in the 10-part Talon SS test than in this one.
For those who are following this series, this is the first accuracy test. Today, I’ll test the barrel made by Dennis Quackenbush with a twist rate of 1:12 inches. I’m testing with two pellets at this time — the 14.3-grain Crosman Premier and the 15.9-grain JSB Exact. You’ll soon see why I’ve chosen to test with just two pellets, as there are several variables that each required testing. I’m trying to limit the number of shots in each test.
Following today’s test, I’ll do the same thing with the factory barrel and also with the other barrel Quackenbush made with a 1:22 inch twist rate. Then, I’ll write a report that analyzes the data from the three accuracy tests. After that, I plan to shoot each barrel at 50 yards for accuracy, but that will probably be done on power setting 10, alone, unless there are compelling reasons to do otherwise.
I shot the rifle at two distances — 10 meters (11 yards) and 25 yards. Each pellet was tested on each power level — zero, 6 and 10. If you forget how those levels are controlled, you can find them described and shown in Part 2. The standard was a 10-shot group. Because the Talon SS is so easy to shoot (it requires no special holding technique), I went with just one group. There’s always the possibility of returning and shooting additional groups after everything has been tested; but as we’ve learned from reading this blog, a 10-shot group is very representative of the true accuracy of a rifle.
There were no called fliers in this test. While that sounds incredible for 120 aimed shots (yes, 120 shots!), I was resting the rifle in the groove of a large sandbag while shooting and it was extremely stable. I did note on one test of the rifle at zero power immediately after filling the reservoir that the pellets were stringing wildly (about 6 inches) in the vertical dimension. I threw that test out and shot another group with the same pellet after the reservoir pressure had dropped a bit. That one seemed reasonable.
I shot 20 shots on zero power (10 with each pellet) and 20 shots on power level 6. The reservoir was refilled before I shot 20 shots on power setting 10 with both pellets. I did this at 10 meters and again at 25 yards. I have some things I want to say about this test. Before I do, let’s look at the results.
At 10 meters, the first test was with both pellets on power setting zero. Before I tested the gun, the rifle was zeroed so the pellets would land close to or inside the bull I was aiming at, but not hitting the center — as that was the aim point for every shot. As always, it’s the group size I’m concerned about — not where the pellets land.
Premiers made a 10-shot group that measured 0.509 inches between centers. Though the group is large for a Talon SS, in my experience, it’s fairly well distributed. So, the barrel made by Quackenbush seems to be accurate enough for this test. We know from the velocity test that Premiers average 452 f.p.s. in the 1:12 barrel and the velocity spread is 56 f.p.s.
Ten JSB Exacts made a group that measures 0.578 inches between centers. That’s just a little larger than the Premier group. It’s also a bit more horizontal than vertical. We know from velocity testing that this pellet averages 434 f.p.s. in the 1:12 barrel, with a spread of 56 f.p.s.
Power setting 6
Moving up to power level 6, I fired one shot to see where the pellet was going and to allow the valve to adjust to the new setting. Ten Premier pellets made a group measuring 0.408 inches between centers. Velocity at this power setting averages 777 f.p.s. in the 1:12 barrel, with a spread of 63 f.p.s.
Ten JSB pellets made a group that measured 0.419 inches between centers. It was really too close to the other group (of Premiers) to make a distinction; but when I measured it, that’s what I got. The average velocity on this setting with the JSB pellet is an average 786 f.p.s., with a 41 f.p.s. spread.
Power setting 10
Moving up to power setting 10, I fired one shot to set the valve. Then, 10 Premiers made a 0.281-inch group. The velocity at this power setting averages 846 f.p.s., with a spread of 16 f.p.s.
Ten JSB pellets made a group that measured 0.286 inches between centers. Once again, the difference between the JSBs and Premiers was really too close to call. At this power setting, the velocity averages 830 f.p.s., with a spread of 15 f.p.s.
That concludes testing at 10 meters. Now, it’s time to pull back to 25 yards and try everything all over.
Starting at zero power, this was where I discovered that I had to throw out the first group for extreme vertical stringing. After that, though, the gun calmed down and seemed to group as well as it could.
On zero power at 25 yards, Premiers made a 10-shot group that measured 0.903 inches between centers. This is a larger group than I’m used to with an SS, but it seems to be more due to the valve and the velocity variation than the barrel. You’ll notice that there’s a smaller group of 6 shots at the bottom of this group. They were not fired sequentially, though.
Ten JSB Exacts made a group that measures 1.142 inches between centers. Again, there was a smaller group within the large group, but it contains fewer shots than the small group within the Premier target.
Power setting 6
Moving up to power level 6, I fired one shot to see where the pellet was going, plus to allow the valve to adjust to the new setting. Ten Premier pellets made a group measuring 0.375 inches between centers. Velocity at this power setting averages 777 f.p.s. in the 1:12 barrel, with a spread of 63 f.p.s.
Ten JSB pellets made a group that measured 0.979 inches between centers. The average velocity on this setting with the JSB pellet is 786 f.p.s., with a 41 f.p.s. spread. That’s quite a difference from the Premier group at the same power setting/same distance.
Power setting 10
Moving up to power setting 10, I fired one shot to set the valve. Then, 10 Premiers made a 0.753-inch group. It’s still a fairly well-rounded group.
Ten JSB pellets made a group that measured 0.944 inches between centers on power setting 10. This time, the group was not just larger, there were several pellets that did not land in the same place. It’s also strung out horizontally.
What did we learn?
This is just the first test of 3 barrels, so it’s too early to draw a lot of conclusions. But there are things that can be said about this one test. For starters, JSB Exact pellets seem to spread out at the longer distances and higher power levels. Are they over-stabilizing? Too soon to tell, but the Premiers definitely out-grouped them. That may change when we test the factory barrel.
Premiers really only opened up at 25 yards on power setting 10. And they didn’t group well at 10 meters on zero power. Everything else was okay. Are they a more stable pellet? In the 1:12 twist barrel, they seem to be.
In researching this report, I’ve read in several places where gun writers say there is no problem with over-stabilization from fast twist rates. They say that as long as the bullet is stable, there’s no difference in accuracy, regardless of the twist rate. That may or may not be true for bullets (though I doubt that it is), but it certainly isn’t true for these two pellets! That much has been proven pretty clearly.
Beyond that, I don’t think I can say anything else. Next, I’ll test the factory barrel.
This test involves shooting 12 10-shot groups per barrel, so it’s very involved. That’s why I can’t do all three barrels at one time. I hope you understand that.