How does rifling twist rate affect velocity and/or accuracy? Part 6
by Tom Gaylord, a.k.a. B.B. Pelletier
This is the sixth part of a very long test in which we’re looking at the effects of the rifling twist rate on accuracy and velocity. If you have landed here and not read the first 5 parts of the report, I advise you to do so before reading today’s report because I’m not repeating a lot of what went into this test.
I’m using an AirForce Talon SS rifle in .22 caliber because it’s accurate and also because the barrels are easy to change. Dennis Quackenbush has made two barrels with twist rates of 1:12 and 1:22 for this rifle, but today I’m testing the Lothar Walther barrel that comes standard in the gun.
Today, we’re looking at the accuracy of the factory barrel that has a 1:16 twist rate. I’ll shoot 10-shot groups at 3 power levels with 2 different pellets at 10 meters and 25 yards. That means I’m shooting the rifle 120 times for today’s report. Some of you have wondered why it takes so long between reports — this is the reason.
What you’ll see in today’s report was actually shot on two different days because I cannot maintain concentration for 120 continuous shots. So, I shot the 10-meter targets on one day and the 25-yard targets on another. All shooting is off a rest, to take as much of the shooter out of the equation as possible.
First up is the 14.3-grain Crosman Premier pellet with the rifle’s power set at zero. Ten pellets made a group measuring 0.495 inches between centers. If you’re interested in the respective velocities of each pellet at the various power settings, you can find that in Part 2.
Next, I fired 10 15.9-grain JSB Exact pellets on the same power setting. The group measures 0.10 inches between centers. That’s for 10 shots! Don’t tell me that a Talon SS isn’t accurate!
Next, the power was dialed up to setting 6, and I shot a group of Premiers. To see how the power settings are calculated, look at Part 2. Ten pellets made a group that measures 0.404 inches between centers.
Then, JSBs were shot at the same power setting. This time, they landed in a group that measures 0.092 inches between centers. This is better than a lot of 10-meter rifles can do for 10 shots at the same distance. People will argue that they can do better, but it’s always a 5-shot group they show.
Now, THAT is a group! Best one of this test and better than many 10-meter target rifles, it’s 10 shots on 0.092 inches. It looks vastly smaller than the other small group above, but this one has more paper that closed back on the group than the first one.
Finally, we come to power setting 10. Premiers grouped 10 pellets in a tight 0.247 inches. This group is very round, indicating the barrel likes this pellet at this power level.
JSBs at power setting 10 finished the 10-meter testing. They landed in a group measuring 0.299 inches between centers.
Now it’s time to move back to 25 yards and test everything again. First up is the Crosman Premier at power setting zero. Ten made a 0.48-inch group.
JSBs came next. On power setting zero, they made a 0.571-inch group.
Then, the power was dialed up to 6, and Premiers were fired again. Ten went into a 0.654-inch group. That was the largest group fired with the factory barrel in today’s test. This group was also spread very horizontal.
JSBs made a 10-shot group that measured 0.569 inches between centers. This group was also horizontal in shape.
Finally, the power was dialed up to 10, and 10 Premiers were fired again. This time the group shrank to 0.329 inches. I call that a significant result; because not only is this group much smaller than the group fired on power setting 6 with the same pellet, it’s also very round and uniform. I think it shows that the factory barrel likes this pellet at power setting 10.
And JSB Jumbos at power setting 10 produced a group measuring 0.359vinches. That’s just slightly larger than the Premiers. I think the rifle really likes power setting 10. This group isn’t as round, but it’s clover-shaped, which is also good.
Interpretation of these results
I will hold off interpreting the results of all the testing until I’ve shot the 1:22 barrel at 10 meters and 25 yards, but something stands out in today’s test. At power setting 6 and 25 yards, accuracy went out the window. It got better at the low end of the scale and again at the high end; but for both pellets, power setting 6 didn’t seem to work well at 25 yards. Yet, at 10 meters, that setting and JSB pellets produced the tightest group of the entire test.
This is the kind of thing an owner has to do with his rifle with each pellet he plans to shoot. And it’s also why spending an inordinate amount of time examining one specific power setting is useless if you don’t know the big picture first. Look at the JSB target on the zero setting at 10 meters to see what I’m saying.