The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek
First off have the head space checked any reputable gun smith can check this in minutes and should not cost you much. If anything not only for function but just alone for your safety , If all is good then move on to the hammer spring it may be too light or incorrectly installed $0- $7.00 fix and I have had this happen tinkering with my spring weights , one will go off the next may not , I dont think you have a BCG issue because as stated above it worked in another rifle . The H2 buffer is not going to fix your problem. Check to make sure they did not send you a rilfe length spring , it wouldnt be the first time I have seen this happen and it causes FTFs and stove pipes also, What mags are you using ? try a different mag preferable PMag if your having FTF issues and you have the correct length buffer spring in there , another thing to check may be the barrel port hole has a burr or possible didnt get drilled at the right size , this will also cause FTF / FTE issues . Sometimes it will have enough gas to eject and not feed the next round.
If you cannot find the problem with what everyone else and I have stated I dont know what to tell you . Everything has been covered completely
I pulled this from your other thread you had going