AR reloading conundrum

[Perryguy]

Okay, loaded new Winchester brass with Winchester small rifle primers, Sierra 52 grain MatchKing bullets and VihtaVuori N133. With 24.o grains my Service rifle AR functioned well both single load and from the magazine. Strangely, however, with 24.5 grains in single load the bolt did not lock back, it was visible about halfway back in the ejection port. Any knowledgeable folks have any advice for me? Thanks.

 

[bowslngr]

Re: AR reloading conundrum

Sounds like you crossed the threshold of too much port pressure. Your gas system is trying to open the bolt while the brass is still in its fully expanded state (exerting enough pressure against the chamber walls that it resists being pulled out). By the time the brass contracts, your gas system has exhausted too much of its energy to get the job done properly.

 

[Perryguy]

Re: AR reloading conundrum

That makes sense and one thing I forgot to mention was thsat the brass was thrown much less far with the 24.5 gr than with the 24.0.
Thanks.