Velocity Loss In A Gas Gun


This isn’t really a question, but an observation I thought you may be interested in.

Over the years, I have heard the same question asked several times. “Do you lose velocity in a gas auto due to the amount of gas bled off to work the action?” I decided to waste some time on finding the answer to this question. Being somewhat of a Jr. Technoid wantabe, I figured out right away that for the test to have any validity, I would have to use the same gun and barrel. So I took my trusty AL390 and my chronograph and all the different shells I could find and ran some five shot strings. Then I tapped the gas ports and installed set screws in them. I ran the strings again (but for some reason I had to work the action manually). To make a long story short, there was no difference in velocity between normal operation and having the ports plugged. However, I was very surprised at the deviation in some of the popular factory loads. My reloads were generally much more consistant.


Dear Randall,

The tiny amount of gas vented by the little teeny weenie gas ports, as well as the timing of the venting (well after the shot has reached most of it’s eventual velocity) just about guarantees the conclusion you observed.

But, hey! You did the work. No armchair surmising for you. It’s easy to just sit back in the easy chair and sagely opine. I do it all the time. It takes a certain mindset to drill and tap to find the truth when others are just tapping their feet. You have done us all a service. Now, when I get asked the frequent question about velocity loss in a gas gun, I can state some facts instead of my usual groundless opinion.

Randall, for your indomitable pursuit of the TRUTH, you are hereby awarded the coveted Junior Technoid Order of the Palm (third class). This award is granted to those who actually do the work, rather than just talk about it. Henceforth you will be allowed to add the letters “JTOP3” to your signature. In token of this honor you will soon receive (by email, of course) a genuine hand-painted plastic shirt pocket protector, suitable for framing or even wearing if you are into ball point pens and slide rules in the breast pocket.

Well done!

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)

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2 Responses to Velocity Loss In A Gas Gun

  1. Jay says:

    I want to know which popular loads and their variations. I already knew gas bleed off was inconsequential.


  2. tarponhunter says:

    For having the chutzpah to tap and drill the vents which in theory might have messed up the gas system up, he should be awarded 1st class, not 3rd.


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