Hey guys, maybe someone can help me figure out what I should do. I have a bolt action Safety harbor firearms .50 upper conversion that I just can't figure out. I am using a DPMS lower with the SHFA hammer installed. It worked fine in the begining but the firing pin kept breaking. I sent it off to SHFA and they replaced the bolt assembly. Now, when shooting the rifle, ocassionaly(every 4-5 rounds) the hammer will follow the bolt home. I can cylce the bolt all I want but it will not lock to the rear. At this point it will continue doing it unless I split the upper/lower and lock the hammer back manually. Re-assemble and then it will lock back every time. I have let my local gunsmith work on it but he could never duplicate the problem or find anything wrong. I assume there is too much clearance between the hammer and the new bolt. Any ideas?
FWIW...  the upper is #020 so it was one of the first ones he made, gotta figure it would have some bugs to work out.

change hammers and try it out again

sounds like a sear problem
or the bolt isn't moving the hammer far enough back to reset it

Do you have a custom or adjustable trigger?  To me it sounds like a straight trigger problem.  I would trade out the trigger and hammer and see what happens.

Unfortunately it is a $40 custom SHFA hammer setup.  After work I will take it apart and see if the trigger is custom as well or if it's just a Mil-spec.
http://www.safetyharborfirearms.com/images/stories/virtuemart/product/13.025-shf%203162.jpg

The trigger should be mil spec the hammer is the only proprietary parts and you must remove the disconnector for it to work

If the hammer locks when you manually set it, then I think your assumption about excessive clearance between bolt-hammer is logical. I take it this didn't happen with the original bolt assembly that was replaced? Does this lower have one of those nylon snug scews that tighten the upper to the lower? If so you might back that off a bit. It sounds like the new bolt is a hair smaller in diameter and may be able to move upwards in the receiver as it's cycled? Or perhaps the new bolt is not compatible with the old hammer?

As mentioned by previous posters. If you have a mil-spec trigger lying around I'd swap that just to eliminate the trigger as the culprit. Also if you have the heavy hammer spring installed, try and put a stock AR spring in there to see if that helps.

I seem to recall some online talk about a bad batch of firing pins from Safety Harbor. Was it a faulty firing pin or early bolt design that was causing the breakage?