Sadlak Industries precision pistons are made to the exact GI specifications with all critical dimensions individually inspected. The 420 stainless material and heat-treating operations are both certified to assure quality. The pistons have a highly polished surfaced using a non-contact electro-polishing method that maintains tolerance on the critical diameter and does not “round over” the edges on the grooves. The pistons are then hard coated with a gold colored Titanium Nitride (TiN) finish. This coating, often used on machine cutting tools, helps reduce galling and pitting and holds up better to the high heat and abrasiveness of gunpowder and primers. The resulting effect is a smoother action an improved life of the piston and cylinder.
The alteration to the pistons adds a .030/.040 wide groove running along the piston axis on the large diameter. The groove runs
through the gas-port hole for the purpose of equalizing the gas
pressure for a smoother more consistent action. The groove is
ground to the actual GI national match drawing #9352724. The
original GI drawing for the standard piston is #7267047 which does
not specify a polished finish or the groove.
IMPORTANT: THE NATIONAL MATCH GROOVE IS INTENDED FOR NM GRADE AMMO ONLY AND IS NOT RECOMMENDED FOR SURPLUS BALL AMMO OR OTHER LOWER POWER AMMO.
If you plan to shoot NM ammo then the groove in the piston is useful. Otherwise, it was not intended for regular ball ammo (not enough power). The groove provides a more consistent pressure
against the op rod by bleeding off some of the excess pressure
inherent in high-power Match ammo. This results in a slight recoil reduction to help "get back on target" during rapids. It also breaks the vacuum between the piston and the cylinder allowing the shooter to hear the piston slide down to confirm it isn't fouled.
Clarification of What is National Match
The military originally reworked standard M14 rifles into sniper rifles using the specifications and drawings developed for national match competition. Therefore, when first introduced, the military's M21/M25 sniper rifles were actually their national match rifles.
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