Sighting for M1A

[Knarley]

If one moves the gas port selector to not run the action, does that affect shot placement. Tired of chasing brass all over.
KB

[Winger Ed.]

Not that I've noticed.

In relation to the entire muzzle blast, not much is bled off, and what little bit is
gets trapped by the gas piston in the gas block/cylinder and not just vented out/off.

The real test would be to chrono shots with it in both positions.
Even then, I don't think the velocity would hardly vary enough to notice.

[MrHarmless]

I would suggest that you/the gun would probably shoot more accurately, based on the lack of moving OP rod while the bullet it rolling down the boom tube.

Fewer moving parts is generally better.

[country gent]

It will cause a small repeatable variation ( more so on the standard GI pencil barrels). But it is repeatable so a sight setting for on and one for off. On a true match grade the cylinder may not turn off as they were "unitized as part of the accurizing process, The sheet metal front hand guard mount is welded or screwed to the gas piston. This gives a solid mounting for it with the lip to stock joint and hand guard. There are ways of lighting ejection on these rifles that work very well and just dribble the cases out, though they do take some trial and error.

A modified gas plug will tone ejection way down. Set the plug up in the lathe and drill a small hole thru its end ( I usually used 3/32 .093) then a larger hole at 10-32 tap drill 1/4" deep. And tap to bottom 10-32. now pick up some 10-32 set screws 1/4" long. drill holes thru them starting at .050 at each number size to .093. You now have a ported gas plug and can adjust the extraction ejection by changing the screws. Tune the extractor and its spring, then the face of the ejector and its spring.

My NM built M1As with this plug ejects the brass from full power load on my mat just in front of my stool. 9 out of 10 shot string fall in a ball cap sized pile. The last one is close but the bolt lock back messes up the group. This was and probably still is service rifle legal mod. Shutting of the port isnt

[PHyrbird]

Went to the range last week. Used my homemade fishnet brass catcher. Didn't lose one case. It even gathers 22LR. Cost less than $10. Ugly but works....

[Larry Gibson]

On an M1A/M14 the bullet, even a cast one moving at 1800 - 2000 fps will have cleared the muzzle/barrel before the oprod begins moving to the rear. As previously mentioned, a small amount of variation of POI between the two may be found depending on load and range at which tested.

[Mk42gunner]

I can honestly say that I don't know, the only times I ever fired an M-14 with the gas cutoff shut was when I was using for throwing lines while Unrepping or recovering broken down LCACs.

Try it and find out, that is the fun way.

Robert

[Adam Helmer]

If one moves the gas port selector to not run the action, does that affect shot placement. Tired of chasing brass all over.
KB

Knarley,

Why not just go to the bench and find out?

Adam

[Ford SD]

If one moves the gas port selector to not run the action, does that affect shot placement. Tired of chasing brass all over.
KB

the One thing that i have heard that improves repeatibility of shot placement for the M1A Family is a aftermarket Spring guide rod
and tuning the gas system (So it does not move) rattle etc.

the next thing I have heard that improves shot to shot is fixing bad receiver to stock fit.

if you can take a feeler gauge and stick it under the heel and or where the stock/ receiver fits above the trigger group ... it will throw random shots
100% fit up is NOT REQUIRED ...Attachment 260119

this picture is from a USGI fiberglass stock after bedding and before a trim (high gloss bits to be removed)

[Chuck Perry]

A modified gas plug will tone ejection way down. Set the plug up in the lathe and drill a small hole thru its end ( I usually used 3/32 .093) then a larger hole at 10-32 tap drill 1/4" deep. And tap to bottom 10-32. now pick up some 10-32 set screws 1/4" long. drill holes thru them starting at .050 at each number size to .093. You now have a ported gas plug and can adjust the extraction ejection by changing the screws. Tune the extractor and its spring, then the face of the ejector and its spring.

And if you're not handy like that you can purchase one ready to go for less than $70. I plan to get one of these for my SOCOM. http://www.schustermfg.com/m1a-adjustable-gas-plug/

[country gent]

I know Matt and Rich Shuster and have shot with him at local matches. Good people and a true craftsman