M14 Forum

art luppino

Several have asked how to find out if they have short or long Dwell. Take the gas plug out, clean the threads on both the plug and those in the gas cylinder. With the rod in the forward position, in battery, screw the plug in slowly until you feel the piston JUST contact the rod, the rod will began to move to the rear if you continue to screw the plug in. Using a feeler gauge, measure the gap between the top of the gas cylinder lock and the under side of the flange on the gas plug. This is the Dwell in terms of length... There is no set distance that I know of on M1A's.. In general, if the gap is more than .010", this is where I set my rifles, you have more than is necessary and are working towards a short Dwell, the bigger the gap the shorter the Dwell. This distance can be safely modified by cutting off material on the tang of the piston using a lathe. There is Approx 1/10 th. of an inch of solid material at the end of the tang.

The US M14 Service Rilfe used a short Dwell to enhance automatic fire, so I have been told. This is not the best condition for accuracy in my experience. I would not encourage making ANY modifications to the gas plug, including,
venting, unless you plan to shoot bullets over 175 grs. Art

Visigoth9

Thank you for the "how-to" Art. I'll be heading out to the garage for the feeler guage Monday morning.

Now the question, if I have already shimmed the entire GC assembly forward with a .010 shim to get a proper lock-up are all bets off on further tinkering with the dwell spacing?

or is that simply a matter of just using your step-by-step to see if there is residual "piston over run" inside the GC

and also, have I told you lately how much I appreciate your taking the time to lay all these things out for us?

Maybe I'm just remedial.... but after owning and shooting these rifles for at least the past 25 years ,,,
I do feel like I am actually/finally getting a real education on the M14

Please don't stop "pointing out the potential leaks in the plumbing"
Regards
vg9

Ctkelly

I just checked my newest build per Arts instructions. I have .064 gap...so if yours is anywhere near as much as mine even with the .010 shim I'm sure you can do some more tinkering.

I also had another gas piston around and checked it in the gun to see if it would change any...came up roughly the same. As soon as I can get out to the range I plan to test fire the gun and then have the machinist at work begin removing material in ~.015 increments until I get close to arts recommended .010 setup. Interesting to see if there are any benefits/negatives in this little project.

I agree with you...Art has been a great asset in his short time on this board.

fragout2000

Thanks for the info Art. You explained it in such a way, that even I was able to understand.

dprice3844444

How to find your Dwell time..

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Several have asked how to find out if they have short or long Dwell. Take the gas plug out, clean the threads on both the plug and those in the gas cylinder. With the rod in the forward position, in battery, screw the plug in slowly until you feel the piston JUST contact the rod, the rod will began to move to the rear if you continue to screw the plug in. Using a feeler gauge, measure the gap between the top of the gas cylinder lock and the under side of the flange on the gas plug. This is the Dwell in terms of length... There is no set distance that I know of on M1A's.. In general, if the gap is more than .010", this is where I set my rifles, you have more than is necessary and are working towards a short Dwell, the bigger the gap the shorter the Dwell. This distance can be safely modified by cutting off material on the tang of the piston using a lathe. There is Approx 1/10 th. of an inch of solid material at the end of the tang.

The US M14 Service Rilfe used a short Dwell to enhance automatic fire, so I have been told. This is not the best condition for accuracy in my experience. I would not encourage making ANY modifications to the gas plug, including,
venting, unless you plan to shoot bullets over 175 grs. Art


is this with an empty chamber or with a cartridge/gauge in it?

casebro

The way I uderstand this, the pistona nd plu are what stops the op rod's forward motion, by about .010"?

Any thoughts on shimming the gas plug, rather than trimming the piston? Shims are easily reversible. And my gun needs about .060...

NoExpert

That would be less than 1 turn in contact with the piston right? The threads are 64 tpi right? That's about 3/4 turn in contact. Now does this include torquing the plug or no?

GeneCo

Seems to me, the bolt has as much to do as the plug at stopping the op rod's forward motion, but the ideal situation is that the piston hits the plug at the same instant the bolt goes into battery.