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I just received a TRW Parts kit and noticed the OP rod had a tiny hole in the end of it. In the cylinder area centered. I have read about this but cannot remember what it said. Thank you for any replies RTH
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: NoExpert</div><div class="ubbcode-body">What was/is the purpose of it? Mine is old, no vent hole. </div></div>
Harrington & Richardson Arms added the vent hole to its M14 operating rods beginning in 1961. Springfield Armory and Winchester did likewise after 1961. The vent hole on the forward end of the tube section was added to the operating rod drawing with Revision G dated September 29, 1960.
My guess is that the reciprocating action of the operating rod creates a very short-lived but cyclical and slightly higher air pressure inside the tube portion without the vent hole at the forward end. The vent hole ensures equal air pressure at all times between the inside and outside of the tube portion of the operating rod.
I've read the op rod nose can hit some really high temps during rapid or full auto fire (makes sense with the piston contacting it). I wonder if it also serves to try to help cool the op rod nose when moving by using some of that air pressure...