Best of B.B.: Spring gun performance as caliber changes
by Tom Gaylord
Writing as B.B. Pelletier
This report covers:
- Spring gun performance as caliber changes
- .177 caliber
- .20 caliber
- .22 caliber
- .25 caliber
This is a report I wrote in 2008. I selected it for today’s blog because we have so many new readers that I felt it would be good to go over the basics, again. We’re going to discuss the basics of spring-gun power. This report demonstrates how the muzzle energy of a spring gun increases as the caliber increases.
Spring gun performance as caliber changes
This is an indoor test I’ve wanted to do for more than 10 years. Because I own a Whiscombe JW 75 with all four smallbore barrels, I can test how each caliber performs with the rifle set at one specific power level so I can control as many variables as possible.
My JW75 has barrels in all 4 calibers: .177, .20, .22 and .25.
Popular theory says there should be a power increase as the caliber increases. Velocity is unimportant, as we’re looking at power, only.
I also learned last year that .20 caliber is less efficient than .22 caliber when pellets of the same weight are used. I have a supply of 14.3-grain Crosman Premiers in .20 caliber, so when I tested the first .20-caliber Condor I was surprised to see it shoot slower than the .22-caliber barreled Condor with the same pellet. I don’t think it’s friction with the bore, but rather the .20-caliber pellet has a smaller surface area against which the compressed air can push. This test with the Whiscombe should be interesting from that aspect, too. Let’s begin!
I removed the transfer port limiter for today’s test so the gun would run on full power in all calibers. The temperature was 70˚ F, and the humidity was 55 percent. [Note: The Whiscombe rifle has different sized air transfer ports. I was running the gun without them, which means it is wide open — as powerful as it can get.]
That hole in the receiver with the Allen wrench sticking in it is one of the transfer port limiters. For this test I removed it and shot the rifle wide open!
These Allen screws are the transfer port limiters. The one with the tiny hole at the bottom is the 12 foot-pound limiter that was in the gun when I got it. By removing all limiters and leaving the transfer port wide open, you get the maximum power the rifle can deliver. That was how I ran the rifle for this test.
RWS Hobbys averaged 1221 f.p.s. They ranged from 1191 to 1238. The average energy was 23.18 foot-pounds
Crosman Premier 7.9s averaged 1139 f.p.s. The range was 1136 to 1142. The average energy was 22.76 foot-pounds
Beeman Kodiaks averaged 959 f.p.s. The range was 948 to 971. The average energy was 21.65 foot-pounds.
Eun Jins averaged 719 f.p.s. The range was 709 to 727. The average energy was 18.49 foot-pounds.
Let’s look at the same rifle in .20 caliber. Nothing but the barrel was changed for this test.
14.3-grain Crosman Premiers averaged 847 f.p.s. The range was 839 to 860. The average energy was 22.79 foot-pounds. In .20 caliber, the Crosman Premier weighs 14.3 grains — the same as .22 caliber.
Beeman Kodiaks averaged 858 f.p.s. The range was 851 to 863. The average energy was 21.75 foot-pounds. In .20 caliber, the Kodiak weighs 13.27 grains, making it a light- to medium-weight pellet.
Eun Jins averaged 539 f.p.s. They ranged from 518 to 554. The average energy was 15.29 foot-pounds. They were very tight in the breech and hard to load.
Next, I swapped the .20-caliber barrel for a .22. Again, there were no other changes to the gun. This is what I got.
Crosman Premiers averaged 906 f.p.s. The range went from 904 to 908. The average energy was 26.07 foot-pounds.
RWS Hobbys averaged 983 f.p.s. The range was from 975 to 990. The average energy was 25.54 foot-pounds.
Eun Jins averaged 580 f.p.s. They ranged from 571 to 590. The average energy was 21.22 foot-pounds.
Finally, I installed the .25-caliber barrel. Again, nothing has been changed except for the barrel.
Diana Magnums averaged 813 f.p.s. They ranged from a low of 807 to a high of 819. They produced an average energy of 29.36 foot-pounds. Diana Magnums weigh 20 grains. They were tight in the breech and loaded hard.
Beeman Ram Jets averaged 725 f.p.s. The range was 719 to 728. The average energy was 28.25 foot-pounds.
Beeman Kodiaks averaged 571 f.p.s. The range was 549 to 592. The average energy was 22.45 foot-pounds. They were an extremely tight fit in the breech and had to be hammered in with a rubber hammer. I would not have used them, had I not been doing this test.
Here are the top energies observed for the four calibers tested in this rifle.
.177: 23.18 foot-pounds
.20: 22.79 foot-pounds
.22: 26.70 foot-pounds
.25: 29.36 foot-pounds
So, except for the .20-caliber barrel, there’s a linear power increase as the caliber increases. I have no way of knowing if I’ve hit on the most powerful pellet in each caliber — in fact, the odds are against it, except perhaps in .177. There might be a much better .20-caliber pellet that would vault the .20 above .177, where we all think it belongs. The relationship between the calibers, however, (.177 lowest and .25 highest) will probably remain in this order when the best pellet for power is determined.
The .20-caliber barrel for this rifle seems to be on the small side, as two of the three pellets were snug. Only the Kodiaks fit well. The .25-caliber barrel was also snug. Of all four barrels, the .22 seems to fit the most pellets.
I was surprised that .20 caliber was less efficient than .177, but that’s just in this particular rifle. However, .20 caliber is also behind .22, where I expected it to be. In the late 1990s, the British airgun magazines had an ad campaign that touted the .20-caliber Crosman Premier as more effective over longer range than the .22. I think my experience with both the Condor and now the Whiscombe disproves that, or at least makes it suspect. In the same powerplant, I have twice seen .20-caliber Crosman Premiers go slower than the .22-caliber Crosman Premiers of the same weight.
If this same test were run on the AirForce Condor, I would expect the relationships to remain as they are, with the exception of the .20 caliber that I think would surge ahead of .177. However, the heavier pellets would produce more energy than the light pellets, in all likelihood.