The easiest way to determine if it's a chamber issue is to run a go-gauge in the chamber. I just had to 'adjust' a factory Rem 700 Sendero in 300WM because the bolt wouldn't close on it. Had to run the reamer in .003" to get it to close freely.
Send the rifle back if a go-gauge fails to chamber. Even slight resistance is a bad sign.
Checking the ammo is also simple, run it in a comparator and measure it.
I check all ammo, factory and handloads with RCBS Precision Mics, best tool you can get for measuring brass as you can measure the shoulder datum even with a bullet in place.
Cheers.