Garand - McCann Adjustable Gas System questions


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transalpian
March 9, 2009, 12:30 PM
Greetings!

I just received my adjustable gas system from McCann and would like to ask for input from the forum.

Is there a correlation somewhere between powder burn rate (and/or standard commercial ammos) and appropriate gas jet? Or is a truly trial and error process?

What methods have you used to mark the individual gas jets? They all look pretty much the same externally, even though I know they have different size holes in them.

I kind of expected a jet without a hole to allow for use of M2 ball. Can I simply use a hex socket cap screw without a hole?

What else should I know?

thanks in advance!

'alp

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SlamFire1
March 9, 2009, 02:31 PM
Is there a correlation somewhere between powder burn rate (and/or standard commercial ammos) and appropriate gas jet? Or is a truly trial and error process?

The only correlation I can tell you is the slower the powder, the bigger the hole.

You are not going to be able to look at a powder brand, or burn rate, then reach in your baggie and find the "proper" vent hole size. Too many varibles.

What methods have you used to mark the individual gas jets? They all look pretty much the same externally, even though I know they have different size holes in them.

I used my eyeball to look at the hole sizes.

I kind of expected a jet without a hole to allow for use of M2 ball. Can I simply use a hex socket cap screw without a hole?

Sure. But I would still use a vented screw. As long as the rifle functions throughout the entire clip, using a vented screw is easier on the brass. This rifle, and every other gas operated mechanism, they all open up when there is a residual pressure in the chamber. In a military capacity it improves function. But it is hard on the brass. The case gets stretched during extraction.

Leaving the vent in there adds a little dwell time, the breech pressure is a little lower on unlock, and that is easier on the brass.

What else should I know?

If your rifle is a rack grade, you won't notice much difference on paper. However, in a match Garand, you will be surprised how much the group is moved by vented gas plugs, and when you change the vent size, the group moves again.

I do not recommend this as a way to shoot bullets heavier than 175 grains in the Garand. I tried shooting 190's in mine. Even though I found a vent that barely functioned the mechanism, I could tell that the heavier bullets were hard on the rifle. Accuracy was not as good as standard loaded 175's.

transalpian
March 9, 2009, 03:17 PM
Great feedback! Thanks!

'alp

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