With a bolt action rifle, it is assumed that trueing a bolt face enhances accuracy.

With an AR-15, what impact does the bolt/bcg have on accuracy with many companies selling premium bcg’s?

Now that is a great question. I'm all ears.

That is a good question. I’m interested too.

Don’t have a real experiment to point to but…

I bought a young manufacturing BCG for my “sniper” AR and that gun is super accurate with factory ammo.

The barrel is aftermarket. (Douglas)

Figured if it wasn’t accurate there was nothing more I could change.

'Premium' applies to coating, correct dimensions of parts, gas leaks, etc. Chamber/barrel/alignment are more important. It's a pressure cap on the end of the barrel. It's movement variations are more important.

The only way we've seen a BCG effect accuracy is when the gas key ID and the OD of the gas tube aren't lined up correctly. As duffas mentioned, premium refers to things like:

Material, 9310 bolts are the best and are stronger than Mil-Spec Carpenter 158
Dimensional tolerances
Coatings

Accuracy of an AR is pretty much determined by the bore and chamber quality of the barrel. Quality barrels will have bores that have been honed prior to rifling, have been double stress relieved and chambered properly on a CNC machine for consistency. Run of the mill barrels have had the bore hone and stress relieve steps skipped.

Ammo can have an effect on accuracy in an AR too. When a round is chambered in an AR while firing (this is a pretty violent action) the bullet can actually be slightly bent out of alignment having a negative effect on accuracy. We've seen this the most with the 350 Legend caliber due to its rough feeding. I've personally experienced loads that will shoot sub 1" in bolt guns that won't shoot much under 2" in an AR with both having the same bore spec..

Good stuff.

This was good info. I've wondered this one myself over the years. Good to know cause I like to know where I can cheap out when need be.