So I finished my build this evening, and in a safe environment chambered a round. I did not fire the rifle, just function checking. I picked the round up, and noticed two things:

#1- I was fairly alarmed to find a slight dimple in the primer of the round. I've owned AR's before, but never paid this much mind. Does this indicate a head space problem, or something worse?

#2- The case was fairly marred around the rim from chambering, and ejecting the round.

I'm going to get some pictures up ASAP. Figured I'd ask while I get my laptop out,

slight dimple - totally normal, the firing pin is free floating - just to be cautious, you wouldn't want to chamber that round over and over.  Once or twice no problem.

get some dummy rounds/snap caps to test feeding and ejection. A slight dimple can be pretty normal.

Thanks Hater, I was wondering about that with the firing pin being free. Just caught me off guard to see that. Chambered the round twice before I noticed the dimple, then pitched the round.

I do need to invest in some. I placed the rifle on safe and pointed it towards a tree line a few hundred yards across an empty field. No houses for miles past the woods just to be safe. But you're right, that will be much safer.

I am by no means an ar expert. But have you cleaned the new barrel specifically the chamber it could help with your feed/ejection issue could be something left from shipping to the finishing.  Again not an expert just a suggestion I think a lot of people overlook cleaning a new barrel

I have kind of played with the thought of installing a small spring on the firing pin to keep it pushed back into the bolt carrier. I do know some AR10's have this feature.

V

There is no feeding issue. The AR is designed with a free floating firing pin, and it's also designed to only let the firing pin go forward far enough to fire it when the bolt is fully locked. Not ever before. That is because self loading actions are not like manual actions, and this is one of the examples.

Along with that is the inertia of the pin is calculated to be less under any condition that could ignite a military primer. And it works, it's never been a reported problem with the M16/M4 in over 45 years.

If you are an accomplished gunsmith and have a good working knowledge of the self loading design of the AR, you could add a spring. And that change would require other changes to compensate for the lighter strike on the prime. That would require a heavier strike by the hammer, accomplished by a stronger spring.

Problem being the hammer spring is what you feel as the pound weight of the trigger pull. The pull weight would go up to get the hammer to strike harder. Oops, unintended consequence.

Be careful what you ask for. A firearm is designed by people who have to consider every cause and effect in the chain of events leading up to ignition - and making sure it only happens when it should.

Like the others said, the slight dimple is 100 percent normal. I would be scared if I chambered and extracted a round and it didn't have the dimple. As for the rim markings, post pics so we can diagnose it

pics of the rim will be needed..


does it by any chance have long gouge marks scraped into it?
i've had metal magazines do this to the bullet and neck of a cartridge (during pickup and insertion into the chamber)