I picked up an m4 I built for my son yesterday while at my grandsons birthday. Son says its failing to eject rounds, asked him when this started. He said five years ago. " and he's just telling me about it" anyway the build is

Upper is a MUR-1
Lower is a Mur, " VLTOR" Noveske stamped.
Recoil is a A5 VLTOR.
BCG is a , LMT enhanced set.
Rails are CASV -M,
Sights are Troy HK hooded, style.
Sporting a VLTOR pinned Gas Block, don't remember which gas tube.
Gresselle, straight trigger.

So I've not confirmed via shooting the rifle. I reviewed the Bolt, LMT, see zero signs of wear, chips, dents, etc etc.

Would I be correct in getting into the gas system next? I'm stumped. I build, I'm a novice, when it comes to you guys here, in fact that's why I'm back.

Back when I built this was the best of the best stuff to build with. It's clear to me, I screwed something up. This rifle has o 10 exact copy brother rifles, they all run fine.

Any assistance is greatly appreciated.

Thank you guys in advance.

Dirk