My 308 had the same problems the first time I took it out. The plastic mag.s were so tight it took both hands pulling back and forth to get the mag.s out.
A guy I met here on this board let me borrow a SR-25 mag and and old original AR10 mag. I took the bolt / carrier to work, sprayed it down with PB Blaster, ran hot water over it, dryed it with air gun, lined the gas rings, then lubed it up with a light coat of Castrol air tool oil.
I took it back to the range,and she ran like a champ with both mag.s, deadly accurate.
I bought a DPMS 7.62x39 the same day as the .308 did the same damn thing. Did the same to the bolt / carrier, will see what happens.
DPMS are very fine AR's I own four different ones. Nice workmanship, great fit between upper and lowers, quality parts, very accurate.