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.
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.
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.
They started popping up again a couple years back. They got popular for a little bit until people figured out that they won't cycle reliably with bullets <168grs.
In some rifles, its a you need too try one first or loan one from a shooting buddy and see if your load works with it or not, both pistons I have work in both of my rifles with loads as lite as 125grs.
If it doesn't work out they sell pretty quick in the PX so your not out alot of coin.
Didn't Broofield Precision Tool make an improved piston for the M25? Any idea what the improvements consisted of? Difference in plating techniques, perhaps?
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