How does rifling twist rate affect velocity and/or accuracy? Part 2
by Tom Gaylord, a.k.a. B.B. Pelletier
Let’s begin our look at the effects of the rifling twist rate on accuracy and velocity. This will be a huge test. I know many of you will want to know THE ANSWER sooner than I get to it. All I can do is ask you to be patient because this has never been documented for the public, if indeed, it has even been done before.
We’re testing the 1:22″ twist barrel that Dennis Quackenbush made for the Talon SS test rifle. I’ll use the velocity figures that I recorded for the factory barrel several months ago in the 10-part Talon SS report. After I’ve tested the 1:10″ twist barrel (in the next report), I’ll also retest the factory barrel following the exact test structure I’m using for both Quackenbush barrels. I know my rifle very well and don’t expect the numbers to be that far off. So, you can accept today’s figures as gospel, but I’ll retest the gun just to make sure.
I followed a fill process that’s very exacting, so each test is the same as all others. I’m not going to bore you with the minutiae, but I discovered while testing the gun on the lowest power setting that the velocity climbed after about 5 shots immediately after a fill, so I refilled the reservoir after each test on low power. On the higher powers, the gun is very stable across the useful fill, so those tests did not all begin at 3,000 psi. They were tested with 2,600 psi to 2,800 psi in the air reservoir — a range where the velocity is extremely regular.
I’m going to use only two pellets initially. Until I learn something about the performance of these barrels, it’s not worth spending endless time running down “facts” that don’t really matter. Later, if the data indicate a need for expanded testing, there will be additional velocity tests with other pellets.
The best way to view the results is when they’re grouped by power setting. Each pellet was tested with the rifle set at three different power settings. Since my gun doesn’t have a scale on the power adjustment window, I put a piece of tape there and marked it for the two higher power settings. The lowest setting is with the power screw indicator as far to the left as the window permits.
Tape marks the two higher power settings. When the screw head is centered on the index mark, the power is correct. When the screw head is as far to the left in the window as it will go, the power is on the lowest setting.
Power setting 0
On zero power with the factory barrel, 14.3-grain Crosman Premier pellets averaged 486 f.p.s. the range was from 451 to 522 f.p.s. That is an average energy of 7.5 foot-pounds.
On zero power, 15.9-grain JSB Exact pellets averaged 507 f.p.s. The range went from 498 to 521 f.p.s. At the average velocity, this pellet produces 9.08 foot-pounds on this power setting. And the spread is 23 f.p.s.
The velocity spread for both pellets is on the high side, with Premiers being the highest at 71 f.p.s. That tells us the valve is not too stable at the lowest power level and a full fill of air.
On zero power with the 1:22 barrel, Crosman Premier pellets averaged 534 f.p.s. The spread went from 499 to 569 f.p.s. — a range of 70 f.p.s. At the average velocity, this pellet produces 9.08 foot-pounds of muzzle energy.
On zero power with the 1:22 barrel, the JSB Exact pellet averaged 521 f.p.s., with a range from 482 to 528 f.p.s. That’s a spread of 46 f.p.s. At the average velocity, this pellet generated 9.59 foot-pounds of energy.
Again, there was a high velocity spread for the Premier pellets, and the JSBs were tighter. With both pellets, the muzzle energy increased with the 1:22″ twist over the factory barrel.
Power setting 6
On setting 6, the Crosman Premier pellets averaged 787 f.p.s. from the factory barrel. The range was from 775 to 800 f.p.s., so the spread was a tighter 25 f.p.s. At the average velocity, this pellet generated 19.67 foot-pounds of energy.
On the same setting, the JSB Exact pellets averaged 778 f.p.s. with the factory barrel. The range was from 769 to 785 f.p.s., so the spread was 16 f.p.s. At the average velocity, this pellet generated 20.57 foot-pounds of energy.
The Crosman Premier pellets averaged 840 f.p.s. from the 1:22 barrel on power setting 6. The range was from 831 to 847 f.p.s., so the spread was a much tighter 16 f.p.s. At the average velocity, this pellet generated 22.41 foot-pounds of energy.
On setting 6, the JSB Exact pellets averaged 817 f.p.s. from the 1:22 barrel. The spread went from 810 to 824 f.p.s. At the average velocity, the energy generated at the muzzle was 23.57 foot-pounds.
Power setting 6 boosted the power a lot. It also stabilized the velocity quite a bit with both pellets. As you can see, the 1:22″ barrel outperformed the factory barrel by quite a lot. This is especially noticeable when you look at the muzzle energy.
Power setting 10
The Crosman Premier pellets averaged 854 f.p.s. from the factory barrel on power setting 10. The range was from 850 to 860 f.p.s., so the spread was a very tight 10 f.p.s. At the average velocity, this pellet generated 23.16 foot-pounds of energy.
On setting 10, the JSB Exact pellets averaged 823 f.p.s. with the factory barrel. The spread went from 821 to 825 f.p.s., which is just 4 f.p.s. At the average velocity, the energy generated at the muzzle was 23.92 foot-pounds.
Crosman Premier pellets averaged 854 f.p.s. from the 1:22 barrel on setting 10 — the identical speed they got with the factory barrel on this setting. The range was from 844 to 863 f.p.s. Although the average was the same as for the factory barrel, the spread was much greater at 19 f.p.s. At the average velocity, this pellet generated 23.16 foot-pounds of energy.
On setting 10, the JSB Exact pellets averaged 815 f.p.s. from the 1:22 barrel. That is LESS than it was on power setting 6. The spread went from 809 to 819 f.p.s. At the average velocity, the energy generated at the muzzle was 23.46 foot-pounds.
Power setting 10 is as high as I ever run my Talon SS. I haver determined that with a 12-inch barrel any setting above this one just wastes air. While the velocities may be a little different with the different twist rates, I believe the general rule will hold that setting 10 is as high as any 12-inch .22-caliber barrel wants to go — at least with the powerplant on my rifle.
The results of this test
As you can see from these results, the gun is wasting air on power setting 10 with the 1:22 twist rate. It is much more efficient on power setting 6. And it does not give up any power to the factory barrel, leading me to wonder if a 1:22″ twist rate might not be a better rate for .22-caliber pellets in the middle power range.
The factory barrel edged out the barrel with a slower twist by getting 23.92 foot-pounds of energy from JSB pellets on power setting 10 compared to 23.57 foot-pounds with the 1:22″ barrel shooting JSB pellets on power setting 6. I don’t know what that says, but there it is.
We’ve learned a little from this test, and we now know there’s so much more to be explored. The results were not as dramatic as some might have anticipated. Many thought the slower 1:22″ twist would have sped up the pellets noticeably, but that didn’t happen. What it did seem to do was make the rifle more efficient in the middle range of power.
It’ll be interesting to see what the 1:12″ barrel does under the same circumstances. After that, I’ll retest the factory barrel at these test settings to verify they’re correct.