I will chim in with my two cents.
The stock stag10 barrel is chrome lined, and is very durable. Just take a look at the life expectancy 15000-17000 vs a stainless or Chrome Moly at 5000 -7000. Being chrome lined I seriously doubt and damage was done.
About the bullets getting pushed into the necks, there are many things that could do that. Firstly seeing how this batch of ammo is a known bad, I wouldn't be surprised if they were improperly crimped and the bullet got pushed into case inside your magazine when firing due to recoil. Secondly take a look at your feed ramps from he barrel extension. They should lined up with two small cutouts in the upper receiver. In the AR15 world they are called M4 feed ramps, and if they are not lined up properly can cause all types of bad things to happen. Thirdly, if you are worried about your chamber being "Cut" just take a ball point pen and run it gently through your chamber and see if get caught on any ridges or deformation. You are using the pen as a "feeler"
IMHO it's just bad ammo. Split necks cant hold bullets under tension, and will cause the bullet to get pushed into case under recoil inside the mag.
Ive had new recruits run their C7's literally full of sand and dirt, pumping hundreds off rounds threw the newly created "Sand blaster". If also seen ammo that was oiled and then covered with sand and dust, and then promptly run threw the guns as well. Never seen a bad chamber, and all these guns still hold around 1-2 MOA. All this was due to lack of experience of course.
Cheers,
Chris