I was in the process of finding out why my carefully measured handloads were getting the bullet setback into the case.  I bought these 150 grain Remington Core-Lokt factory rounds, measured them, and then dropped the bolt on the first round to see if it did the same thing.  The round is stuck on the feed ramp with the bolt pushing on the case head.

http://i259.photobucket.com/albums/hh284/CTone03/Gun%20Things/100_5927.jpg


Here's a look at the feed ramps:
http://i259.photobucket.com/albums/hh284/CTone03/Gun%20Things/DSC02534.jpg


I've also had problems with rounds hitting the inside of the magazines as well.  Here's an earlier post.

Any ideas on how to keep this from happening?  It's a .308 Winchester with a 20" FA barrel and bolt in a DPMS upper and lower.  I'm eyeing those feed ramps with intent to Dremel.  

Either get a magazine feed lip tool from Brownells or a set of smooth jawed pliers and ever so slightly bend the front 1/2 inch of the feed lips up.  Not much at all, maybe 1/64 an inch max.  That will let the round ride a little higher out of the mag and your problem will be solved.  I had this happen to all three of my PRI 6.8 mags.  Do not bend them up much or they will drag on the bottom of the carrier and create a whole new set of problems.  Just a tiny bit will do it.

I would check a few mags first. Make sure the notch isn't allowing it to sit too low. Also, try an extra power or new mag spring and anti tilt followers. The round may just be nose diving a bit.

ETA: Beat me to it.

I had rounds hanging up in the feed ramps on a 20" AR. I replaced the buffer spring with a Wolff spring and the problem was solved.

I do a lot of modify of guns for reliable blank fire.  Had a guy bring me a DPMS 308 that had this exact problem.  The easiest fix was to tig a .030" bump on the back of the magazines spine right at the bottom of where the mag well ends.  100% reliable with those US Army blunt nose blanks.  Should have the exact same results for you on those blunts.  If you rock your mag forward while firing you will likely find that little bit of slop will be taken out and it will work fine.

BTW I have modded several armalites and NEVER had this problem with them.  Of course they have a 3 degree angle on the mag wells the DPMS appear to lack


EDIT:     DONT DREMEL!!!!!!

Roger!! Don't Dremel!

Thanks much for all the advice.  I'm glad it's not me as this is my first from-scratch build.

I think I'm going to try all of the above.  First thing is probably going to be the Brownells mag lips tool first as it gives me an excuse to order some stuff from them.  I might try ordering a new buffer and spring from FA too as it is their bolt/barrel/extension that I am using, or maybe from Wolff as I will be looking for their mag springs to order.   Save some money on shipping costs.

If that fails then I will give VZ58's remedy a try.  I understand what you're saying and it makes sense.  I'll post a report once I get this thing taken care of.

Thanks again!