Hi guys.  I have a BM 16” lightweight upper on a Cav arms lower with a RRA bolt group.  I have put just over 1000rds through it with out any problems at all up to now.  I shoot mostly Wolf and xm193.  The upper was used when I bought it but the bolt group and lower were new.  Here is my problem.  The last three times I have been out the gun has jammed once every time.  I am usually shooting only 40rds per outing.  It jams in a very specific way, stove pipeish.  The un-ejected case is caught on the neck by the bolt at the very front of the ejection port, so it is sticking straight out in a very obvious manner.  Initially I just thought this was a fluke because it was so strange but three times in a row has me wondering.  What is going on?  I have checked the ejector spring and it is very stiff and strong, which makes sense since it is a new bolt.  I doubt it is shot stroking because it always resets the hammer and the recoil indicates otherwise.  What is going on?  Why now?      

That bolt does not have to travel very far back to cock the weapon. It just might be short-stroking. Check the gas key or look for a broken gas ring

Never hurts to lube the ejector according to the TM.  Solved my problems with stove pipe issues.