Compensators - Fact or Fiction ? Read this...

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By: Rada
Credit: http://www.topgun-airguns.com/testing-compensator.html" onclick="window.open(this.href);return false;

Note: Tests here were done with PCP Pistols, between 9 to 10+ ft/lb

QUESTION: Would a higher velocity or 12 ft/lb PCP rifle, yield SIMILAR or completely different results... with or without a compensator attached to a rifle at 20 yards , at 50 yards ? Please update us, if you can do a similar experiment.

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(abridged where necessary)

Testing With and Without a Compensator

For some time now I have been hearing questions regarding compensators. Are they needed? do they help? how much accuracy can you get from them? Are typical examples. Prior to this article I believed they helped but not to what extent. What exactly they did to accuracy or to a certain pellet I have not caught in print. So I set out to do a small experiment for myself.

First I picked a pistol that has the greatest amount of adjustability to the compensator and one I could shoot with the compensator removed. This was my silhouette pistol: Tau-7 in .22 caliber and 12 inch barrel. First I shot a ten shot group with the compensator set at an arbitrary setting which became my datum point. Ten shot strings were shot datum plus 2 mm and datum minus 2 mm. Finally the compensator was removed for the last ten shot string. The sights were not adjusted except for when I removed the compensator and installed the regular front sight. Then I just sighted in the pistol with another pellet not used in the tests.

Since we are on the pellet subject. Pellets selected were typical of what I have seen shooters use at our silhouette range. Pellets chosen are a small subset and cross section available to the shooter. You will note that there are no flat head pellets in this test. Not because shooters do not use them but because it has been my experience that round head or semi pointed do better. The reader is urged to test their favorite pellet with the compensator and gun of their choice. The Crossman pointed head was selected since it shares the range record here in Phoenix. The Hunter by Air Arms was its' counter part, the rest are domed heads.

Testing was done indoor so the weather was not a factor. Range was 18 yards, same as the ram setting, range temperature was 80 F. The pistol was shot sandbagged with the large CO2 bottle left attached. I didn't call any flyers. The ones that you see are unexplained. Since silhouette is shot in 10 shot increments I shot 10 shot groups (this writer believes 10 shot groups are a better indicator of accuracy in the real world). All pellets were seated by hand not by pellet seat. After the test was complete I did set my pistol to slightly lower velocity and managed much better groups.

In conclusion: A compensator does have a substantial effect on what the pellet does down range. Some pellets will respond better then others. But the shooter also must be aware that velocity effects group size also. Do compensators work alike? I would say yes, very similar no matter the design but never the same on the same pellet at the same speed. My recommendation would be to test your preferred pellet at different speeds and different compensator settings on the muzzle. A good example would be the Premier.

There was over a half inch difference on settings, I bet if the velocity was adjusted this pellet would shoot great. Another good example was the Air Arms Field, it did not like the compensator, shooting the best group without it (indeed, after the testing was completed a half inch group was shot after the velocity was reduced). This test has intrigued me so much I may try a similar test with a 10 meter type pistol.


.... ..Crossman Premier.....RWS Superdome ....Air Arms Hunter........Air Arms Field.................Crossman Pointed

Zero:
........1.347 ctc................0.913 ctc..................1.802 ctc...................1.069 ctc................0.977.ctc......

-2mm:
.......0.931ctc................1.564.ctc......... .........1.232.ctc...................1.232.ctc................1.749.ctc........

+2mm:
......1.038.ctc...............1.402.ctc...................0.854.ctc...................0.916.ctc................1.684.ctc.........


...No. Comp
.....1.565.ctc...............1.441.ctc...................1.441.ctc...................0.624.ctc................1.371.ctc......


Here are the statistics for the pellets as to velocity and energy , for accuracy refer to the above chart.

Crossman Pointed
Average velocity 549.9 fps.
Velocity spread 7.0 fps
Energy 9.53 foot pounds
Weight 14.2 grains

RWS Superdome
Average velocity 540.4 fps.
Velocity spread 27.0 fps.
Energy 9.27 foot pounds
Weight 14.3 grains

Crossman Premier
Average velocity 537.2fps
Velocity spread foot 13.0 fps
Energy 9.10 pounds
Weight 14.2 grains

Air Arms Hunter
Average velocity 534.5fps
Velocity spread 4.0 fps
Energy 10.15 foot pounds
Weight 16 grains

Air Arms Field
Average velocity 538.2 fps
Velocity spread 6.0 fps
Energy 10.28 foot pounds
Weight 16 grains

Interesting to note that some pellets, even though the same weight, have different ballistics. I suspect a difference in diameters is the reason.

THIS IS THE FOLLOW-UP OF THE ARTICLE

In previous tests with compensators I used the Tau7/22 in .22 cal. and several different pellets. For this test I simplified and concentrated on one pellet to see just how accurate it can be made using a two different compensators. Again I used a Tau-7 this time in .177 with polygonal rifling. The test gun is a prototype that never made it to full production and had been proven very accurate from some previous testing. In fact it is rated at 5mm extreme spread for 5 shots at 10 meters.

The two compensators were from Tau and Aeron. The Aeron compensator can be seen in some pictures on Robert's web site(http://www.citlink.net/citlink/s/stevent/" onclick="window.open(this.href);return false;) and it came standard on either the Chameleon or B-96 pistols. This compensator along with the JSB 8.1 grain pellets were supplied by Top Gun Air Guns (T.G.G., 480 513-3778). I thought a great addition to the accuracy testing would be a scope. Also from T.G.G. is a one piece scope mount that slides over the barrel and is held in place by four allen head screws. The rail is standard 11 mm and is high enough to accommodate just about any scope you care to mount on it. The mount also is longer to one side so the eye piece of the scope can be placed above the rear sight for silhouette shooting. Or it can be reversed to mount any red dot sight the shooter wants. For the scope I chose a Tasco 3-12x40 with adjustable parallax and target turrets. I kept the scope on 12X power for all the testing. Shooting was done at 10 meters over sandbags with the bulk bottle left attached for added stability.

I mounted the compensators to almost the muzzle then moved the compensator forward in increments of 3 mm. So I have a zero, + 3 mm and + 6mm for both compensators. I believe that 10 shots is more indicative of accuracy so all groups are shot in increments of 10. First group was shot without using any compensator at all. The group measured .443 inches center-to-center (c.t.c.) and it absolutely horrified me. I thought I grabbed the wrong tin of pellets or there was something wrong with the pistol itself. Then I remembered I never have shot the pistol without a compensator. The first group with the Tau compensator measured .134 c.t.c. for 10 shots. This smaller group made me feel much better. I remembered the .22 did not have such huge differences in group size when the compensator tests were performed on it. But then I am comparing apples and oranges, or is that fruit with vegetables? The next group almost made me rethink the 10 shot theory. First five pellets went through almost the same hole. It was one of those picture perfect moments where a pellet will not fall through the same hole it just made. But then I did say 10 shots so I shot the second five and they opened the group to .123 c.t.c. making it the smallest of the test.

It's difficult to compare the two compensators; the Tau and Aeron. First the Tau is a rather complicated affair compared to the Aeron. Aeron is very similar to the Walther, a basic double baffle. Also notice that the second group using the Aeron is rather large compared to the other's. At first I thought maybe flyers or just bad pellets, but the group is concentric so that is not the case. I need to also mention the pellets were not sorted in any way nor were they sized. They are right out of the tin, lightly lubed using my Proprietary Household Pellet Lube (PHPL) aka. Lemon Pledge. A pellet seat was used for all the shots. But I still can not explain why that one group is so large in comparison. Pellets just simply did not like that setting. That is as scientific as that gets.

I also need to mention the velocity . The first 10 were chronographed without any compensator. Then only the first 10 out of the respective compensators and there was no change in average velocity. Velocity was set at 476.8 fps +1- 3 fps at 79 F. Come to think of it that is not bad at all for a CO2 pistol.

Conclusion: This particular Tau benefits greatly by a compensator. Testing a compensator on several settings is beneficial to accuracy. A quality optical site is a huge help for accuracy testing. It would be interesting to see how Mr. Nygord's compensator would do on this pistol. I am willing to bet the group would be very similar.

................................................................ Group without a compensator. (.443 )

Tau compensator
Zero setting; .134
+3mm/ .123
+6mm/ .144

Aeron compensator
Zero setting; .139
+3mm/ .310
+6mm/ .125

[Jon]

All its doing is altering the harmonics by shifting the miniscule weight closer or further away.
Barrels vibrate, its the tuning to get exit of pellet at top dead centre or bottom dead centre. At end of down or up stroke the barrel has to momentary stop and that's where you want pellet to exit barrel.