I have  a bushmaster lower and a M&A parts kit gun. I am using a brand new parsons mag. The problem is when I go to chamber a round th nose of the bullet will not pass through the feed ramps. Can I sand a radius on the feed ramps/bolt locks or should I take to dealer to fix?

Try a different mag

What kind of ammo???

I had a similar problem with some thin jacketed ammo...45 grain Winchesters I believe...

The narrow bullet with the thin jacketing would get stuck in the feed ramps, sometimes shoving the bullet down into the case and squeezing the sides of the bullet in a little.
I switched back to 55 grain FMJ ammo and the problem immediately went away...

I have also encountered a few barrels with "burrs" on the feed ramps, but they still worked OK.

Of course switching mags is always a good idea, but you indicated that you had a new USGI mag...SO, check your ammo...

Just something else to think about...