Help: m1a gas system edition

So, this might be the wrong place for this, but I thought I would reach out to the brotherhood.

I have a Springfield National Match m1a. The thing is a tack driver but wont cycle reliably.

I took it to a gunsmith who claimed that for some reason m1as can sometimes require higher grain rounds. He messed with it some, with some success.

So here is what I have noticed. If I shoot 7.62 or 308 in the 150s grain range it basically doesn't cycle. If I run 160s grain 308 it cycles maybe 50 percent of the time.

I am thinking of just running heavy 308 through it. So how high can you safely go with an m1a before you, say, mess up the op rod?

Any other thoughts on the issues I am having?