Having played with both M305 and AR's wrt improving accuracy, I can say the process of shooting is no different. Yes, the triggers are usually heavier and may be less then ideal but the basics don't change.
So, if after the best rifle set up you can do, coupled with the best match ammo you can make, and shot under the best conditions including environmental and rests/optics, the rifle doesn't shoot, accept the rifle doesn't shoot.
I did some testing with other semis with great reputations for accuracy. Unfortunately, those particular rifles never came close to what some shooters were reporting. Was my rifle a dud or was their particular accurate? who knows... doesn't matter.
I tested as I would any precision and competition rifle. what I found was the inconsistency typical of semis. good group followed by many more that were ho hum or downright bad.
So the average without discounting any bad group showed the rifle to be less then stellar.
I have built up rifles that were sub MOA accurate and this was at a consistent basis using my handloads. Even got an AR to provide some groups approaching 5/8 min at 100yds. Very exciting but compared to a well set up bolt rifle, not even close.
For the AR, barrels from Shilen, Krieger, and McGowen are possible
for the M1A and M305, kriegers are possible
See the manf websites for all possible options. will they make a significant improvement? you better believe it.
But if I want itty bitty groups both near and far, I will put my money on a bolt rifle.
For consistent sub MOA performance, semis can make that happen today.
Jerry