Thank you Sir. Exactly what I was looking for.You are the only one that knows if it will be safe in your rifle. If there's no pressure signs, then you could work your way up to 42gr. I think 3345fps with a 75gr in an 18" barrel is smoking. I maxed out around 3550fps in a .243 with a 26" barrel running IMR 4350. I would say you have to be really close to max right now or you're already at very high pressures. I would be happy with where you are and would be focusing on precision and consistency at this point.
Out of an 18 inch semi auto I wouldn't be disappointed with that but it wouldn't surprise me if you could go a little faster yet.I'm loading 75gr Speer Varminter bullets behind 41.5gr of H4895 for my 18" barreled AR10. The chrony averages 3345. Is that decent for a 75gr bullet or can I bump it up to 42gr safely in a (full) semi auto?