This is a normal function of the parts combination that you have. It is also why the face of the hammer was redesigned a while ago. What you have is an older hammer.
If you look closely at the face of the hammer, you see that notch on the top where the face seperates from the hook as it goes back? You can take a dremel or a file and put a bevel on it, and it will cure your problem. The newer hammers don't have that step, and make a smooth transition with a rounded edge and flow into the hammer back hook. Fix 1=replace the hammer with a new model or file off the sharp edge on the hammer you have. Even the much touted Jewell AR trigger redid their hammers with a beveled edge because the sharp cut face often times will cause the same problem that you're experiencing.
If you look closely at the bottom of your carrier, you notice that the head of the firing pin is open, and at the bottom of the ramp for the hammer as the carrier cycles. The "Enhanced" as well as the M16 carriers have the ramp significantly further back, thus shrouding the head of the firing pin and preventing this problem. Fix 2=get an enhanced carrier.
If you are experiencing this level of damage now, with 250 rounds, you will eventually round off the shoulder of the pin, or you will begin breaking firing pin retaining pins. Although this looks like it may be normal wear, I do not accept it after only 250 rounds. Make a change to the hammer, replace the pin, or replace the hammer or carrier to eleminate this problem.
Just so you don't think I'm talking from the armchair, I just fixed two ARs of my own yesterday, both new builds like yours, that had the same problem. One completely tore out the firing pin at round 153, and the other was causing the carrier to hang up once in a while on the fwd stroke. ALL of my parts were Bushmaster, purchased from a mail order BM dealer.
I hope that this helps. Don't let it go on, you'll only be dissapointed. Gotta love product improvement.
Tom