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NM Piston - question answered

2K views 11 replies 7 participants last post by  Phil “Murphy” McGrath 
#1 · (Edited)
What is the difference between a NM piston and a standard one?
 
#2 ·
On the Sadlak NM piston I believe there is a groove that equalizes the gas pressure for a "smoother more consistent action". Read the info lower on the attached for specifics.


[ame]http://www.amazon.com/Sadlak-Industries-National-Cylinder-Pistons/dp/B003MA61T4[/ame]
 
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#5 ·
No, but there was a drawing and drawing # assigned, Sadlac makes a piston per the NM drawing #. Standard USGI pistons were hand grooved by unit armorers. I have both a std USGI piston that was hand grooved and a Sadlac TiN grooved piston I cannot tell and niether can my rifle what shoots better. YMMV.

There is a feelable differance in the rifles recoil, a std piston is sharper akin too a slight jab too the shooters shoulder, a grooved piston is more of a shove/push too the rear.
 
#7 ·
The groove came about while firing ammo that weighted more than 190grs, the atempt was too slow down the op-rod and prevent cracked rec heals. The name that I heard connected too the groove was Bill Donovan, even thou the 190 still didn't work well there was a side effect less barrel deflection.

There is a short slow motion vid on you-tube of a M1a firing, in slow motion you can see a few things going on at the same time, one is the gas system, it pulse 6 times with each firing from each ring on the piston as it travels too the rear, you can also see the barrel flex/whip up and down from each venting, in real time this looks like on event, with a groove piston there is one continous pulse and the barrel flexes less.

I think this time frame was when std barrels were the norm, medium and heavy barrels flex/whip less do to there added mass, that doesn't mean they don't flex, add a grooved piston too any barrel weight and the noodle effect is minimized that much more.
 
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