Just fired a new build of frankenstein parts.   Had an interesting series of the rifle firing then I got a click, no primer dent at all.   It seems to be caused by the cam pin twisting slightly and blocking the firing pin.  That lower has never had a light strike with other uppers.   It was tight in the bolt and was very hard to turn.   I'm pretty sure it was causing the problems but after discovered I was down to just a few rounds on the range trip.  I tried that pin on a colt bolt and it wouldnt even fit in.   Is there any problem to filing it down to fit better or should I just replace it?   I also had some iffy functioning in general with various failures.  It was ejecting brass towards the front of the rifle  My Colt throws it far off towards the rear.    What functioning difficulties would be barrel related?   The bbl is stamped 5.56 and I was shooting XM193.   My Colt ate it just fine out of the same usgi mags.  So far this frankenbuild isnt working so well.  Also curious if my carbine buffer might effect functioning?   What would be indicitave of a buffer/spring related failure?  

FSB appears cast, has a line down the backside looks like casting flash ground off.   16"bbl, stamped 5 56 in bbl looks like it was stamped by hand.  No roll pin, a rivet with round head flared at one end holding on sling swivel.  Looking closely at the upper the brass deflector has taken a pounding, that's probably why the brass was flying forward.  The FSB looks to have a C on top right side and what looks like a bell at the portion where the gas tube inserts.   Headspace has not been checked, I'll see if my local shop has a go/nogo gauge set.