How does rifling twist rate affect velocity and/or accuracy? Part 11
by Tom Gaylord, a.k.a. B.B. Pelletier
Continuing our look at the 3 different twist-rates, today I’ll shoot the factory Lothar Walther barrel at 50 yards. The factory barrel has a 1:16″ twist rate that has become ubiquitous for airguns and is the very thing this test is designed to examine. Last time we looked at how the 1:22″ twist barrel did at 50 yards, with 2 different pellets fired at power levels 6 and 10. Today, we’ll see the same thing with the factory barrel.
This test was performed yesterday, and the range conditions were perfect. There wasn’t a breath of air to be felt for most of the shooting session, and only an occasional puff of air later on in the morning after I swapped barrels for the final test. I’ll report on that set of results in the next report. Today is devoted to the factory barrel.
The AirForce Talon SS shoots with a fill of 3,000 psi, so before the test I filled the reservoir. Twenty shots would be fired at power setting 10 and another 20 at power setting 6, plus one shot at the start of the test and when the power wheel was changed. I haven’t reported that fact until now, but it’s my standard practice when shooting at 50 yards with a Talon SS.
Valve needs to be exercised
I have learned that the Talon SS valve needs to be fired one time following power adjustments to get it set at the new power level. The first shot will usually be like the gun was on the previous power setting, but the second shot will be solidly at the new setting; so I always take one shot to set the valve with every fill and at every power change.
Shooting off the bench at 50 yards on a perfect day with the Talon SS was enjoyable.
Power setting 10
I started with power setting 10; so when it was time to shoot on power setting 6, the reservoir would have less than the full fill pressure. That way, I knew the gun would be right in the middle of the power curve.
The first pellets I tested were 14.3-grain Crosman Premiers. Because the groups had dropped so far below the aim point in the previous test with the 1:22″ barrel, I dialed up the elevation several clicks for this test. I was hoping to hit the bullseye with the new sight setting, but Premiers on power setting 10 still dropped about 3.50 inches at 50 yards. Ten Crosman Premiers went into a group measuring 1.567 inches between centers. While that’s on the large side for a Talon SS in my experience, it was still a very round group.
At 50 yards, 10 Crosman Premiers went into this round group, which measures 1.567 inches between centers when the power was set to 10.
JSB Exact Jumbo
Next, I switched pellets to 15.9-grain JSB Exact Jumbo and shot another group of 10. This was also at power setting 10, so the gun’s valve did not need to be awakened. These pellets hit about 2.50 inches below the aim point, so they landed higher than Premiers at the same sight setting. This time, the 10 pellets went into 1.283 inches — a much better group than the Premiers, though there was a hint of vertical elongation to this group.
Ten JSB Exact Jumbo pellets made this 1.283-inch group at 50 yards on power setting 10. This group is slightly vertical.
The difference between the Premier group and the JSB group was evident through the scope without walking down to the target. Clearly this barrel likes the JSB pellet better. What did surprise me was that even on this perfect day I did not shoot a group smaller than one inch. I’ve done that so many times in the past that I sort of expected it — especially on such a perfect day. Well, it just demonstrates the difficulty of shooting such tight 10-shot groups at this distance.
Now, I cranked the power wheel down to 6 and shot both pellets, again. The first shot settled the valve at this new setting, then the groups began in earnest. JSBs went first since I’d just finished shooting them at power setting 10.
This time, 10 JSB pellets went into a group that measured 1.53 inches between centers. It was larger than the same pellets on power setting 10, but smaller than the Premiers on setting 10. The group is fairly round, though most of the shots are clustered on the right side.
Ten JSB Exact Jumbo pellets made this 1.53-inch group at 50 yards on power setting 6. Notice that 7 of the 10 pellets landed on the right side of the group.
The final group was 10 Premiers fired on power setting 6. They made a group measuring 1.261 inches, which is the best group of the 4 shot with this barrel. It’s more open than the best group of JSB pellets, but the overall measurement places it at the top of the ladder.
Did you notice that the pellets crossed in their performance relative to power, with JSBs doing best on power setting 10, while Premiers did best on power setting 6? I wouldn’t make too much of that because we don’t have enough data to make any conclusions, but it is interesting. In the macro, it does appear that Premiers prefer lower power while JSBs prefer higher power — at least at 50 yards.
I have to admit that I was surprised not to see even one group that measured less than one inch. I’ve shot so many small groups with this rifle that I expected it this time, at least with one of the four groups that were produced.
In the next report, which is the same shooting done with the 1:12″ twist, there will be a surprising result. So, there’s still more to come.