Short Stroking and may not be gas block


Hi I purchased a complete upper, 18" barrel, rifle length gas system, .223 wylde stainless H barrel, and I’m using one of my own BCG that works in other rifles. It is short stroking. Tested with AE 55g (xm193) and it ejected brass,but very weak and will not pick up another round making it a single shot. Pleased to say that the barrel showed some accuracy that made me happy. Now I know this is usually a misaligned gas block (low profile) so I’m adjusting it and testing it now. The barrel gas port looks good and the alignment seemed okay so my question is more of what to do if the gas block is aligned and it still short strokes? Here are some important details to troubleshoot…

I noticed a considerable amount of gas blow back in my face. It made me cough and at the end of about 40 rds felt like I smoked a cigarette. Anyway, it shouldn’t do that. Gas block leak? Gas escaping instead of directing to the gas key? Gas key is solid and not loose.

So if I align the block and it still does this, does that mean the gas block or tube is out of spec? Or could gas be escaping the chamber due to an improperly installed barrel? Remember, it still ejects the cartridge with no marks or damaged brass.

It’s mated to a carbine lower with carbine buffer and spring so it’s not too heavy for the rifle length to function.

Any help is appreciated. Could be just a misaligned gas block, but the gas to the face had me concerned about a bad gas block. Never had that much blow back before so gas is escaping the chamber/bcg somehow. Weaker ammo like Tula won’t eject at all just fyi. So low gas is definitely the problem. Hope to solve it, because after 40 single shots, the barrel showed some impressive accuracy at 100yrds with basic AE 55g factory stuff. Most shots landed within 1.5"



Update: Took upper back to range and adjusted the gas block in multiple positions using a pencil mark to line up block with gas hole. No luck, still short stroking. Either the hole is too small or the gas block and/or tube is defective. Any other suggestions? I’m probably going to return it and forget it.


Believe it or not, I went through that. It turned out to be the o-ring on the extractor had swelled. Removed o-ring and running without it. Been running great.


I had the same issue with a 223 build. I used an adjustable gas block and with is wide open I still had the issue. It would not lock the bolt back after the last round. It was an AR Stoner barrel bought from Midwest. 20" stainless 5r barrel. Ended up enlarging the gas hole in the barrel. I don’t remember the drill size but I do remember I went 1 drill size larger. Clamped the bit in a pair of vise grips and drilled the hole by hand. It surprised me how easy it was to drill. Took 1 minute. Mounted it all up and closed the gas block 3 clicks. At the range It worked just like it should.


I’ve been noticing that a lot of barrels lately are undersized. take a pair of calipers and check hole sizing.


That’s good to hear; i see I’m not the only one. The port was .094" which is usually the min for 20" barrel with rifle gas system (so I’ve read). I ended up doing the same and will have the port enlarged just a tad, test fired, then opened more if needed. I should have it back by Wednesday. The company that put it together also was helpful and said they’d do it all on their dime if I decided to do so. Hoping I’ll have a working 18" upper on Wednesday.


I wonder why they’d leave an 18" with the same port hole as a 20"+ standard. Maybe because they see “rifle length gas” and drill for that standard. Or, they may assume folks with the 18" will be using light carriers and buffers for the lightest possible recoil impulse. No clue, but I’m having it checked and slowing opened up to correct the issue. Everything else looked good so hopefully that solves it.


Check your gas key and make sure it is tight to the bolt carrier and isn’t leaking. Check your gas tube button and make sure it isn’t worn on one side. Check all potential gas leak problems before you drill the gas port. I had to drill a brand new Faxon 20" barrel for proper function. Always put a cleaning rod in the barrel while you drill so you don’t drill too far and hit the opposite side of the gas port inside the barrel. I have a big drill bit set with incremental drill bits. I opened my gas port four times before I hit the sweet spot. An adjustable gas block works great if you open the port too much. Some manufacturers will have gas port sizes for NATO spec ammo which will not run the lower pleasure stuff like Tula.


Checked all that and it was good. 62 g Xtac 5.56 wouldn’t even lock the bolt back. It’s good to see others needed to drill the port bigger to get proper functioning. I wonder why this is needed for some barrels. Do they not take into account the length of barrel after the port? I read on another forum a guy needed to do it on his Ballistic Advantage barrel too. I would expect these barrels to come working from the factory, though I understand leaving it at a minimum for the gas setup so the user can adjust as needed. A lot of companies are drilling 16" barrels to be over gassed a bit so they run all ammo types and have less customer complaints. I’m new to 18" barrel with rifle length gas system and hope I get it working after opening up the port. I had a local gunsmith agree with this remedy and also the maker of the upper said they would do the same if I sent it back to them. I was looking to see how common this was before I went ahead and altered the port. Thanks for the incite! Maybe it’s just a mass production standard… I read (of course it’s the internet so not sure how true) that custom companies the specialize in upper setups like White Oak drill the ports to a spec that works with the length and gas system.


The first barrel I had to increase the port size was a 16" Bushmaster back in the 90’s. The larger the port size, the more recoil impulse will increase. Adjustable gas blocks can fine tune the load for perfect recoil impulse as long as the port size is of proper size. Hope you get it figured out.


Going to open it in small increments based on a factory 55grain .223 load until it operates smoothly. Should give me a good range of cheap ammo to heavier reloads to function well. After ruling everything out, hopefully that will be the fix. I don’t see any other likely culprit. Thanks for the input.


So get this… opened the port to .999 (0.100) and absolutely no change in cycling. Still just puffs out the brass and won’t lock back. I called the company to send me a replacement gas block and tube. Other than those leaking too much gas, I have no idea how it couldn’t work from here. If it doesn’t work after that, they will replace it for me or refund it.


It could be an improper recoil spring, buffer, misaligned or defective buffer “receiver extension” tube creating excessive friction, defective gas tube in the button area, etc. Is there excessive carbon around the gas block indicating a poor fit? Out of spec receivers can cause all kinds of problems with the hammer- BCG function. Without the rifle in front of me it can some times be a daunting process finding the actual problem. This is why I only use certain AR parts manufacturers. Any AR problem can be found, it just takes a process of elimination to find. Please keep us informed on any new developments. Good luck.


Well the lower works on other uppers and so does the BCG, so it must be the gas tube, block, or the receiver is out of spec. The receiver fit more snug than my other upper, but not in a bad way. I don’t notice excessive gas at the block, but it happens so fast I couldn’t tell. Not much carbon in relation to any other upper as some leakage is normal. They are sending me a new gas block and tube to test to see if that’s the issue. If not, it must be the receiver hanging up on the hammer… even the lower could have the hammer too high, but again it works with other uppers that fit less snug. If nothing works, they are sending me a complete replacement or refund.


That is why I said to check extractor o-ring. I found it on mine, by accident. I am thinking that it was swelled, not allowing extractor let go of case soon enough. Hitting the port opening and slowing the bcg speed, enough, to short cycle, eject and not put a new round in the chamber. It happened to me on a gun that I bought, and had worked perfectly for a few months.


The bcg currently works in other uppers


Who was the manufacturer of your bolt?


It’s not labelled, it’s from another rifle that I didn’t put together, but it works fine. Looks like it could be ARstoner from Midway or one from midsouth shooter supply wherever these folks contract from. It has that distinct shape on the carrier. It is a nitride 9310 MPI bolt and 8620 carrier. Had this and a PSA premium (toolcraft?) 158c and tool extracter blah blah… never noticed any issues with either.


Not to sound like captain obvious, but something is either restricting your BCG from cycling fully or it is a gas problem. Have you tried removing the bolt from your BCG and tried sliding the bolt carrier shut to see if the gas tube is lined up with the gas key. There should be zero restriction between the gas key and gas tube. If your BCG works in another rifle it would seem the problem lies elsewhere. Having excessive gas in your face when shooting is a big red flag there might be a gas problem between your gas key and gas tube. Excessive gas leaking from the gas block should not be flying in your face. I would also look for a crack in the gas tube near the upper receiver.


Yeah, I tested and no hang ups with BCG…smooth as butter through receiver. Didn’t notice any cracks in the tube, air blows through it okay by mouth, had it all a part and back together and still wouldn’t cycle. Only enough to kick the brass out. Definitely not enough gas to throw bolt back. Asked for a replacement gas block and tube (from the manufacturer) to test again 13 days ago and never received a tracking number or item even after they agreed to personally pack it and ship for me. Not sure what happened there. Anyway, I’m returning it for a refund to the retailer; they already sent me a shipping label. I’m done screwing with it and I’m not buying a light weight bcg just to get it to function. Any BCG should work if it was gassed properly. I’m glad the return seems hassle free. Too bad, it’s a nice upper and probably just a faulty tube or block as I’ve trouble shooted everything else except completely different lower and bcg. But I shouldn’t have to wait almost 2 weeks for the dang parts. I’m not that mad, means I can go shopping again :slight_smile: