Adjusting the M14 Op Rod/Piston Length

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Cobber

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Granite tells me that if you unscrew the gas plug on your M14 that the op rod travels a little fartehr forward. I gather that there is something that you can then do to eliminate this.

First, I don't know if this has been covered elsewhere, it isn't in the stickies. Second, I am not sure what this change is supposed to improve. Longer life of the gas system parts? Or maybe those elusive, one ragged hole at 500 yards, groups!

I unscrewed the gas plug on my Norc. Yes, the same one that had the hammer whacking against the cocking tab. (M14 wont fire reliably thread).

I then screwed it back in until it stopped against the gas piston. There is about 60 thou or more gap. Granite says that if I machine something I will eliminate the gap.

My piston is chromed on both ends so that's not where I want to start. My lathe is big but not big enough to swing the op rod in such a way as to machine the front end of that.

that leaves the back end of the gas plug. Is this the way to go? How far do I want to go? Just so that the gap is eliminated and the op rod moving forward will stop just as the piston reaches the gas plug? Or am i after something in between that's just right?

Also, do I make the measurements with the chamber empty or with a primer-less reload to simulate the working conditions? In other words with bolt having just closed on a round with the full pressure of the ejector spring in play to slow down the closing of the bolt and perhaps adding a bit of resistance the forward travel of the op rod. This as opposed to the bolt slipping easily into place on an empty chamber.

Maybe I am making a lot out of nothing but I do like to understand the theory and practice behind these mods. I can see that if this mod is done right then the slamming effect of the op rod/piston on the gas plug might reduce vibrations and or tensions.

Looking forward to the collective wisdom being provided in answer.
 
You are talking about adjusting piston dwell time.
I wouldn't even try it without doing some serious research.
And have a few spare pistons on hand just in case.
Personally I would leave it well enough alone as it is a whole lot of effort for minimum gains. Unless of course it's a several thousand dollar competition rifle and every step must be taking to achieve a desired result.
 
The forward movement of the op rod is stopped by the piston. The piston is stopped by the gas plug. Not sure why an adjustment is needed in this area; however, if you shim your gas cylinder, you are efficetively increasing the op rod forward travel.

Consequence of having the op rod stopping later is that it might not stop on the piston but instead on the bolt roller. That would be bad, very bad.

I'm not aware of any accuracy that can be gained form playing in this area.

R
 
Find art luppino's comments on this and follow what he says closely.
The adjustment is done to the piston tail end, do not mill the plug or the open end of the piston, doing this will begger your gas port alignment big time
 
Yup, just like Granite posted before, BUT... big disclaimer: Do this only if you have a MATCH barrel; otherwise you will hardly notice the results. I don't even do this to my standard Norc barreled M14. Now, once I get enough money for a Krieger from Juanvaldez or Tac-Ord, or a McGowan from M14Doctor.... THEN I will do this 'timing of the piston'. :D

Cheers,
Barney
 
Adjusting "Dwell Time" is something I have had to do with several chop mod 18.5" barrelled norcs as they where gas flow sensitive and adjusting dwell time by fine tuning the piston tail seemed to be the answer.
You gotta be careful, there's not much thickness at the tail end. Also, remove too much and your oprod comes to rest on your bolt roller.
This is not an adjustment done by the layman. Gain a solid understanding of why this mod is done and the correct practices to perform the task ;)
 
I have been doing my online searches for more info on why and how to do these mods. Other than the Tony Ben posting from 2010 can anyone suggest anywhere else that this might be dicussed. I don't think Kuhnhausen (sp?) touches on this topic and the majority of my gunsmithing tomes are intended for more common sporting arms. I know that there are at least two other books on the subject of working the M14 (can't think of titles at the moment) but I wonder if anyone has these or knows if the subject is covered.

I appreciate that adjusting the dwell may delay the moment when the bolt is released. That may reduce vibrations affecting the rifle during firing and certainly will reduce the pressure in the barrel/cartridge so reducing the tendency of M14's to tear the spent case out of the chamber. I understand that removing metal from the inner end of the gas plug may affect the gas chamber volume though I am not sure what the effect will be. The volume will be reduced slightly but as a percentage, how much. That would tend to speed up the gas cycle.

With respect to the op rod over camming the bolt roller I can easily see how this would be a problem. It was interesting to see that on my Norc that with the gas piston completely removed the op rod would not move forward far enough to strike the rear of the gas assembly. I wanted to confirm that before even thinking about shortening the gas piston. Since the gas assembly is not stopping the op rod the cam on the roller is most likely the place though it is tricky to see visually and needs confirmation with spotting compound.

So, lots to investigate and I especially appreciate Hungry's comments on match barrels. It would be a shame to chew through a coupa thousand rounds of reloads trying to test the effects of varying amounts of change to the dwell time. However, I have other rifles for ultimate accuracy. The Norc experiments are just for fun and personal information.
 
Go to m14forum (firing line) .com and read Art Luppino's discussions on dwell time. I am not aware of any books that discuss this... And I have them all, including the personal notebook/log from an ex armourer friend of mine ;)

The piston tail is adjusted on the "outside" not the inside ;)
 
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