The M1As from Springield Armory are usually quite accurate. The trouble I had was keeping them that way. Over time they tend to shake loose. I usually sent them back for rebedding and overhaul about every 2500 rounds.
I understand the newer double lugged receivers are much better.
The gas port on the National Match rifles should NEVER be turned. It is calibrated and turning it will mess things up. I think some of the standard rifle's ports can be turned off. However, I would be hesitant to do it because it will certainly change the barrel harmonics and you would have to develop a different load for the port closed.
I hate to loose brass too, but it really is a minor expense in the overall picture. I am shooting an AR for calling now and loose about 50% of my brass in the field. I buy 1000 cases at a time from IMI (good brass) and don't worry about it.
Enjoy that M1A!
A nice piece of machinery.
