Built an AR15 with an Aero lower, DPMS kit, Tapco collapsible stock, and a SOTA upper with SOTA BCG and carrier.

Symptoms, fires first & chambers first round OK. Mostly does not chamber second round. Fired 20 rounds without loading second round at all. Ejected fired round OK. Had a few rounds where the feeding round was caught by the bolt and jams. Mostly did not strip the second round from the magazine. Wondering if the gas block (clamp-on type) might not be aligned properly, of if the buffer might not be correct weight. Looking for ideas but will be difficult to get to the range for a week or so after doing any repairs.  Not sure what SOTA has in terms of ideas but otherwise  I have to little experiance with these. Last build ran perfect with no issues. Was a Model 1 Sales unit on a DPMS bare lower. Ran well.

Thanks for any help.....

First start with one round in the magazine and fire it, does the bolt lock back on an empty magazine?



Is there any evidence of carbon leakage around your gas block?



Are the gas key screws properly tightened and staked?



What is the Stock?  



What gas system do you have, carbine, middie, or rifle?



What weight and style buffer do you have?

hopefully it isnt a larue upper
I heard it can take years to get it running correctly

but to help some

quite a few things need to be checked
like stated above
the gas block, position and hole size in the barrel

your buffer tube length ( carbine, rifle) , spring type ( count the coils ), buffer weight (weight it on a oz scale or it may have a stamp H, H1 etc )

hammer spring installed correctly, trigger parts working correctly

how far back does the bolt carrier move when pulling back by hand
and if you press it into the buffer tube by hand how deep does it go

Id bet money the you gas block isn't alined right.

I left it at the local gun shop with the smith. He is very know knowledgeable about the AR's. Originally had a problem with the trigger group and he noticed a missing spring to take care of trigger reset and fixed same in a few seconds no charge. . Didn't see anything to tell the weight of the buffer but like was said think it is a gas problem myself. Probably a poorly aligned gas block. That was the first question from the smith also. I didn't build it, just bought it. It was very inexpensive for a free float unit 16" carbine length barrel w/M4 ramps etc. Didn't have a lot to spend so hoped to get it running then upgrade it as money became available. .It is a SOTA upper A125 free float 16 m4 barrel with a replacement front gas block (clamp on type) with a 4 sided rail on it. Otherwise nothing very special about it. Seemed fairly accurate but onl;y fired 20 rounds 1 at a time. Don't have any photos yet but maybe at the end of the week....

OK, runs now. Easy fix. Clamp on gas port was loose, amd obviously not aligned. Shop ran 30 round thru it as fast as he could pull the trigger. Didn't have case with me to pick it up so went back later tonight and gunsmith had left for the night. Oh well, guess tomorrow will take care io it.  Have 100 rounds to use and will zero in the scope. Hopefully tomorrow evening. Guess I was so upset it didn't run that I missed the gas marks around the gas block.

Will post info later.

OK, shot 150 rounds. 223 perfecta, 55 grain 40 rounds, 2 fail to feed, ZO1, WalMart 556 62 grain 90 rounds, 6 fail to feed. It did run but still problems, Narrowed it down to 2 pro mags, just junk I guess. The Tapco ran 99% with a limited number of problems. Rifle was getting very dirty so a few of the problems may have been that issue. Now need to find some decent mags to make sure my diagnosus is correct. Per SOTA arms it should take 200 to 300 rounds to smooth out the upper. Also sometimes the phosphate coating gets into the chamber so I used a copper brush and really scrubbed it out. Hope they are right. Ran it dryer than I would have normally but it was lubed, just not generously. Now it is oily. That and a few new mags and will see what it can do next weekend. No more time this week.

Thanks for the help so far

Great!

But it sounds like you need better mags. Start with USGI straight 20 rd mags or 30 rd mags. Buy new until you know what to look for in a used mag.