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Posted: 5/26/2020 11:22:22 PM EDT
After several decades of building AR’s, I’ve encountered something I haven’t been able to figure out.
Started out to have a CHEAP 7.5” 5.56 pistol build (the FIRST 7.5” pistol I’ve ever built) Original build parts... Bear Creek Armory barrel (hey, it was on close out at $35.00) Brownells Lightweight BCG Rise RA-140 drop-in trigger “80%” Lower I cut out Wolff XP action spring 2.9 ounce carbine buffer On the FIRST shot, the round failed to eject! O.K., I figure it might need some adjustments. THEN I go to eject the fired brass, it won’t eject. The bolt is LOCKED SHUT! Well, I “mortar drill” it to open the carrier and the empty ejects. I inspect the brass casing, it looks fine. I try it several more times, the same result.  Then I try playing with carrier weights, buffer weights, action springs. No matter what combination I try it’s the same result. So I finally come to the conclusion it’s PROBABLY the cheap ass barrel chamber. So I order a Hanson 7.5” 5.56 barrel, same damn issue! At this point I’m ready to switch to a 10” 5.56 barrel as I’ve always been able to make them run.Thoughts? What the hell am I missing?. |
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Posted: 5/26/2020 11:30:40 PM EDT
[#1]
Rough chamber finish, most likely.
ETA: Some issues with dwell in pistol gas systems, but that rarely keeps on stuck in the pipe after, even if it failed to eject during normal operation. |
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Posted: 5/26/2020 11:31:19 PM EDT
[#2]
Really odd it wasn’t that BCA barrel. Did you try another BCG? Would be easy to rule that out.
From there, look at gas block and tube closely...replace if you can. |
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Posted: 5/26/2020 11:34:47 PM EDT
[#3]
Quoted: After several decades of building AR’s, I’ve encountered something I haven’t been able to figure out. Started out to have a CHEAP 7.5” 5.56 pistol build (the FIRST 7.5” pistol I’ve ever built) Original build parts... Bear Creek Armory barrel (hey, it was on close out at $35.00) Brownells Lightweight BCG Rise RA-140 drop-in trigger “80%” Lower I cut out Wolff XP action spring 2.9 ounce carbine buffer On the FIRST shot, the round failed to eject! O.K., I figure it might need some adjustments. THEN I go to eject the fired brass, it won’t eject. The bolt is LOCKED SHUT! Well, I “mortar drill” it to open the carrier and the empty ejects. I inspect the brass casing, it looks fine. I try it several more times, the same result. Then I try playing with carrier weights, buffer weights, action springs. No matter what combination I try it’s the same result. So I finally come to the conclusion it’s PROBABLY the cheap ass barrel chamber. So I order a Hanson 7.5” 5.56 barrel, same damn issue! At this point I’m ready to switch to a 10” 5.56 barrel as I’ve always been able to make them run.Thoughts? What the hell am I missing?. How much you want for a used $35 barrel?  I have several Glock & AR BCA barrels & the ones I've used so far have worked fine.Just like you blamed the bargain barrel, some might wonder about your 80% lower, but I doubt that would be in play with the issue you have. Out of curiosity what upper was it? Did anything seem tight or finicky when cycling by hand? Did you try to cycle any rounds by hand? What ammo were you using? I've never used or even seen that BCG in person so couldn't say too much about that. I think a bit more info could help, me maybe at least, I'm sure some of the more experience guru's might be able to diagnose it with the info so far, but I ain't that good. 
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Posted: 5/26/2020 11:36:48 PM EDT
[#4]
I assume it cycles fine with snap caps?
If not, check the top of the buffer tube/charging handle. I had an 80% lower where I had to take about 1 mm off the top of the buffer tube. |
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Posted: 5/26/2020 11:38:33 PM EDT
[#5]
Check the Bolt and gas system. It could be another bad chamber. Highly unlikely, but possible.
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Posted: 5/26/2020 11:54:29 PM EDT
[#6]
Did you check the headspace!
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Posted: 5/26/2020 11:54:42 PM EDT
[#7]
I’ve tried SEVERAL BCG’s including a full weight M-16 BCG.
It’s not the lower, it runs fine with carbine uppers. The upper receiver is an Aero without a forward assist. I’ve cycled an entire magazine through it by hand with zero issues. Ammo has been Winchester 5.56 M193 and Federal M855 The carrier easily interfaces with the gas tube, no drag. |
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Posted: 5/26/2020 11:55:31 PM EDT
[#8]
Quote HistoryQuoted: Did you check the headspace! Normally I do, THIS TIME I didn’t, that’s next! |
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Posted: 5/27/2020 7:35:43 AM EDT
[#9]
Sounds like you've swapped out all of the parts except the gas tube and gas block. Might not anything getting through.
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Posted: 5/27/2020 7:39:11 AM EDT
[#10]
Betting on gas tube or block.
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Posted: 5/27/2020 7:44:13 AM EDT
[#11]
Quote HistoryQuoted: Betting on gas tube or block. Going with this also. Bad seal on the barrel, not lined up properly, etc. |
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Posted: 5/27/2020 8:31:18 AM EDT
[#12]
My first AR was a bear creek. This was before I knew anything about them.
It would fire and eject 62 grain rounds, but 55 grain would get stuck to the point I had to mortar the charging handle to get it to eject. I figured out that they must not have finished reamed the chamber. The only thing original on that gun now are the upper and lower. Lesson learned. BCA=crap never again! |
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Posted: 5/27/2020 9:53:56 AM EDT
[#13]
Can you open the upper and lower with a case stuck in the chamber? I'd fire a round a then pop the upper and lower open and pull the charging handle to see if the case comes out easy or hard. Easy would indicate the bcg is getting jammed up.
Stuck case/bcg doesn't point to a gas issue. I'm wondering if there's an interference somewhere between the upper and lower where the bolt interfaces with the buffer. It doesn't show up when hand cycling because the slower movement allows it to slide over the interference instead of jamming the carrier into it. Maybe the edge of the buffer tube. I'd look at that area and see if there's any marks. Have you tried a different charging handle? |
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Posted: 5/27/2020 1:01:17 PM EDT
[#14]
Quote HistoryQuoted: Can you open the upper and lower with a case stuck in the chamber? I'd fire a round a then pop the upper and lower open and pull the charging handle to see if the case comes out easy or hard. Easy would indicate the bcg is getting jammed up. Stuck case/bcg doesn't point to a gas issue. I'm wondering if there's an interference somewhere between the upper and lower where the bolt interfaces with the buffer. It doesn't show up when hand cycling because the slower movement allows it to slide over the interference instead of jamming the carrier into it. Maybe the edge of the buffer tube. I'd look at that area and see if there's any marks. Have you tried a different charging handle? Actually, I changed to a Raptor charging handle to get better leverage to try and pull the bolt open. I’ll look into the lower/upper interface but I doubt it because the Brownells carrier has a rounded rear on the carrier. |
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Posted: 5/27/2020 1:07:15 PM EDT
[#15]
If you have to mortar several rounds with several barrels and it never worked....
I'd be concerned about rough chambers or fucked locking lugs on bolt and barrel. Replace bolt this time and see what happens. If no work, replace both. |
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Posted: 5/27/2020 1:18:32 PM EDT
[#16]
Quote HistoryQuoted: If you have to mortar several rounds with several barrels and it never worked.... I'd be concerned about rough chambers or fucked locking lugs on bolt and barrel. Replace bolt this time and see what happens. If no work, replace both. Barrel was changed to a BA Hanson, I’ve tried at least four different bolts. |
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Posted: 5/27/2020 2:32:35 PM EDT
[#17]
An under gassed barrel will stick a case every time. It partially extracts then rechambers the spent case. Ergo, the case sticks in the chamber and requires a lot more force than normal extracting, even mortaring.
Classic under gassing but you are going to have to find out why it’s under gassed. I agree with an above poster, swap out gas tube and especially the block. You’ve ruled out the barrel, carrier, buffer, spring...but using the same gas block and tube. I’d swap them and if that doesn’t work, using good ammo you know that works, I’d be enlarging the gas port. Which leads me to this. Have you checked gas port size? I work mostly with wildcats and I do a lot of gas port drilling. Most will say, and I agree to a point, that enlarging the gas port is a last step but I don’t understand why some are damned scared to do it. Worst case if you go too large is you get an adjustable gas block or reduce port size another way, but it’s certainly not a ruined barrel as some will have you think. My 7.5”, using a 3HB and standard spring, functions perfectly so it’s not the barrel length per se that’s the problem. |
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Posted: 5/27/2020 4:23:37 PM EDT
[#18]
Quote HistoryQuoted: An under gassed barrel will stick a case every time. It partially extracts then rechambers the spent case. Ergo, the case sticks in the chamber and requires a lot more force than normal extracting, even mortaring. Classic under gassing but you are going to have to find out why it’s under gassed. I agree with an above poster, swap out gas tube and especially the block. You’ve ruled out the barrel, carrier, buffer, spring...but using the same gas block and tube. I’d swap them and if that doesn’t work, using good ammo you know that works, I’d be enlarging the gas port. Which leads me to this. Have you checked gas port size? I work mostly with wildcats and I do a lot of gas port drilling. Most will say, and I agree to a point, that enlarging the gas port is a last step but I don’t understand why some are damned scared to do it. Worst case if you go too large is you get an adjustable gas block or reduce port size another way, but it’s certainly not a ruined barrel as some will have you think. My 7.5”, using a 3HB and standard spring, functions perfectly so it’s not the barrel length per se that’s the problem. Interesting thought, I’ll try a different gas tube & gas block and see what happens. |
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Posted: 5/27/2020 4:53:13 PM EDT
[#19]
Maybe take a look at the gas block you installed. A lot of the smaller one are drilled all the way through which makes it possible to insert the gas tube from either end. It might be the problem.
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Posted: 5/27/2020 4:59:46 PM EDT
[#20]
gas tube upside down or gas block on backwards?
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Posted: 5/27/2020 9:12:04 PM EDT
[#21]
PursuitSS,
I'm surprised that you are having problems with as many ARs you have built over the years. I have to agree with others about checking the gas tube and gas block since it sounds like you have checked everything else. I know that 7.5" ARs can be finicky at times. |
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Posted: 5/27/2020 9:14:59 PM EDT
[#22]
Don't give up on 7.5". I've got several 7.5"s, I think 2 are BCA. No problems at all! Most of mine run FSB, but I know the steel sadlac gas block and gas tubes from CDNN have worked for me on numerous builds.
I have no idea what could be going on here, but as others said check your gas block and tube. |
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Posted: 5/27/2020 10:01:26 PM EDT
[#23]
Quote HistoryQuoted: gas tube upside down or gas block on backwards? I did the upside down trick recently. You wouldn't think it would be so easy. I did a painted 7.5" pistol on a cheap combat arms $109 upper with tungsten buffer weights. It ran like a top. |
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Posted: 5/28/2020 7:07:42 AM EDT
[#24]
Searching for gas, I would also pressure check the bcg key. Spray the top of the key good and wet with clp, hold the bolt in and put about 100lbs of air to it, look for bubbles.
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Posted: 5/28/2020 2:02:45 PM EDT
[#25]
Quote HistoryQuoted: Searching for gas, I would also pressure check the bcg key. Spray the top of the key good and wet with clp, hold the bolt in and put about 100lbs of air to it, look for bubbles. I’ve tried multiple carrier groups from working AR’s All of my carriers have properly torqued carrier key screws, mated with Permatex Aviation #3 Form-A-Gasket, then staked with my Brownells staking tool. (Yes, I’m anal on this) |
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Posted: 5/28/2020 2:39:01 PM EDT
[#26]
Hopefully you're like me and you test fired it before you tightened everything down permanently. I just snug things down, gas block and rail, before I test fire, if the test fire gos well then I use red loctite and/or staking on everything.
Anyways, just take off your gas block and verify the gas tube hole lines up with the gas block hole, verify the gas block hole is in the same place as the barrels gas port. Look at the carbon deposit on the top of the barrel. ETA: that'd be really wild if you got 2 bad barrels from 2 different manufacturers. |
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Posted: 5/28/2020 2:43:38 PM EDT
[#27]
Quoted: After several decades of building AR’s, I’ve encountered something I haven’t been able to figure out. Started out to have a CHEAP 7.5” 5.56 pistol build (the FIRST 7.5” pistol I’ve ever built) Original build parts... Bear Creek Armory barrel (hey, it was on close out at $35.00) Brownells Lightweight BCG Rise RA-140 drop-in trigger “80%” Lower I cut out Wolff XP action spring 2.9 ounce carbine buffer On the FIRST shot, the round failed to eject! O.K., I figure it might need some adjustments. THEN I go to eject the fired brass, it won’t eject. The bolt is LOCKED SHUT! Well, I “mortar drill” it to open the carrier and the empty ejects. I inspect the brass casing, it looks fine. I try it several more times, the same result. Then I try playing with carrier weights, buffer weights, action springs. No matter what combination I try it’s the same result. So I finally come to the conclusion it’s PROBABLY the cheap ass barrel chamber. So I order a Hanson 7.5” 5.56 barrel, same damn issue! At this point I’m ready to switch to a 10” 5.56 barrel as I’ve always been able to make them run.Thoughts? What the hell am I missing?. I had this same issue with my lightweight builds when I didn't have a heavy enough buffer and my buffer springs were enhanced or extra powered. The issue you describe is exactly the problem I was having. |
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Posted: 5/28/2020 4:16:51 PM EDT
[#28]
Get that wolf xp out of there.
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Posted: 5/28/2020 5:22:19 PM EDT
[#29]
Quote HistoryQuoted: I had this same issue with my lightweight builds when I didn't have a heavy enough buffer and my buffer springs were enhanced or extra powered. The issue you describe is exactly the problem I was having. Quote HistoryQuoted: I had this same issue with my lightweight builds when I didn't have a heavy enough buffer and my buffer springs were enhanced or extra powered. The issue you describe is exactly the problem I was having. I’ve switched buffers, BCG’s, and action springs till “I’m blue in my face”. Quoted: Get that wolf xp out of there. Long gone. |
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Posted: 5/28/2020 7:02:25 PM EDT
[#30]
I think it's a timing issue. Too much gas, not enough buffer and BCG weight. What's happening is much like what happens when you try to shoot steel cased ammo out of a way over gassed rifle.
Go with a heavier buffer (maybe and H3), at least a standard weight full auto BCG and possibly an adjustable gas block. |
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Posted: 5/28/2020 9:02:17 PM EDT
[#31]
Quote HistoryQuoted: I think it's a timing issue. Too much gas, not enough buffer and BCG weight. What's happening is much like what happens when you try to shoot steel cased ammo out of a way over gassed rifle. Go with a heavier buffer (maybe and H3), at least a standard weight full auto BCG and possibly an adjustable gas block. I’m kinda leaning that way, current attempt has been an M-16 BCG (FULL weight) Standard action spring Heavy buffer (unmarked and no sliding weights) One thing that’s hanging around in the back of my mind is I had to slightly tweak the gas tube to clear the barrel nut for the rail I have on it. Kinda wondering if it might have somewhat shortened the tube? It’s interfacing fine with the carrier key, BUT.... |
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Posted: 5/30/2020 4:59:16 PM EDT
[#32]
Pics of the fired case ?
Looking for a really rough chamber. extraction is being attempted at a very high chamber pressure... so smooth chamber would be very helpful. |
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Posted: 5/30/2020 7:43:06 PM EDT
[#33]
Quoted: After several decades of building AR’s, I’ve encountered something I haven’t been able to figure out. Started out to have a CHEAP 7.5” 5.56 pistol build (the FIRST 7.5” pistol I’ve ever built) Original build parts... Bear Creek Armory barrel (hey, it was on close out at $35.00) Brownells Lightweight BCG Rise RA-140 drop-in trigger “80%” Lower I cut out Wolff XP action spring 2.9 ounce carbine buffer On the FIRST shot, the round failed to eject! O.K., I figure it might need some adjustments. THEN I go to eject the fired brass, it won’t eject. The bolt is LOCKED SHUT! Well, I “mortar drill” it to open the carrier and the empty ejects. I inspect the brass casing, it looks fine. Thoughts? What the hell am I missing?. Had this exact same problem, in my case it was due to using reloaded ammo that was out of spec. You won't be able to tell if the brass is out of spec by just looking at it, need to use an ammo checker to detect this. If the ammo checks out, then try using a go/no-go headspace gauges (though I think ammo is a more likely cause) |
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Posted: 5/30/2020 7:53:12 PM EDT
[#34]
Bad/misaligned gas block, bad gas tube (unlikely unless it's 1/4" too short), bad bolt carrier (maybe not vented properly under the key).
Try a different BCG first. [edit: disregard this since I just read your replies and you've already done it] Did you use the same gas block with both barrels? Maybe start there.. |
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Posted: 5/31/2020 11:03:38 PM EDT
[#35]
Quote HistoryQuoted: Had this exact same problem, in my case it was due to using reloaded ammo that was out of spec. You won't be able to tell if the brass is out of spec by just looking at it, need to use an ammo checker to detect this. If the ammo checks out, then try using a go/no-go headspace gauges (though I think ammo is a more likely cause) Quote HistoryQuoted: Had this exact same problem, in my case it was due to using reloaded ammo that was out of spec. You won't be able to tell if the brass is out of spec by just looking at it, need to use an ammo checker to detect this. If the ammo checks out, then try using a go/no-go headspace gauges (though I think ammo is a more likely cause) I’m NOT using reloads. Federal M855 and Federal M193 This ammo functions perfectly in my other AR’s (same Lot) Quoted: Bad/misaligned gas block, bad gas tube (unlikely unless it's 1/4" too short), bad bolt carrier (maybe not vented properly under the key). Try a different BCG first. [edit: disregard this since I just read your replies and you've already done it] Did you use the same gas block with both barrels? Maybe start there.. New gas tube and new gas block on order. |
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Posted: 6/1/2020 4:28:44 PM EDT
[#36]
In for updates, kinda want to build a 7.5.
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Posted: 6/1/2020 6:47:05 PM EDT
[#37]
Run a piece of wire through the gas block and gas tube. Obstruction free?
What size are the gas ports in the barrels? Are the gas blocks butted up to the shoulder at the gas block journal OR are you leaving a handguard retainer gap? Some mfr's omit the gap and the gas block should be shouldered against the step, some not. Are you getting the gas soot shadow above the gas port to confirm alignment? |
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Posted: 6/1/2020 10:52:38 PM EDT
[#38]
I have found that there are different lengths of pistol gas tubes. I was having trouble with a 6.750" .458 SOCOM build that functioned fine but when I would try to cycle the bolt by hand, it was always sticking closed and took a great deal of effort, almost mortaring, to unlock the bolt. It turned out the gas tube was a hair long and getting jammed into the gas key. I compared the Brownell's pistol gas tube, the one in it, to a DPMS gas tube and the DPMS was about 1/16 inch shorter. I swapped out the gas tube and the problem I had was solved. I have also heard that there are some pistol gas tubes that are shorter than the DPMS tubes but I have not seen those.
Question is, how far back into the receiver does your gas tube come? It should be a least half-way into the half circle cam pin cutout in the upper. If it is short you can experience short stroking even though everything else is A-OK. I had that happen on my .500 Phantom. The gas tube was about a quarter inch too short and short stroking like crazy. I finally realized the gas tube was not far enough back and I was losing gas pressure too soon. The gas key was clearing the tube almost as soon as it was unlocked. I had an adjustable length gas block made which uses a cut off gas tube set screwed into place to vary the length and that rifle's problem went away also.  Attached File |
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Posted: 6/1/2020 11:33:31 PM EDT
[#39]
I had a old ass like 1999 16" ASA barrel that would do that. sold the complete upper and started over.
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Posted: 6/2/2020 4:12:38 PM EDT
[#40]
I just became interested in AR pistols about 6 weeks ago and I am soaking all of this information up. OP I hope you get this pistol up and running on your next try. Now back to the top to read all of this thread again
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Posted: 6/7/2020 8:26:21 PM EDT
[#41]
O.K., I installed a new gas tube. (My new gas block is back ordered)
I pulled the gas block and it appeared to be installed correctly, a dirty ring surrounding the gas port. So I reinstalled the gas block with the new gas tube. I fired a round with a G.I. carrier and it halfway cycled the carrier. O.K., progress! So I installed the Lightweight carrier out of my wife’s AR, a 2A Armament Titanium/Aluminum hybrid carrier. IT RAN!!! It’s got to be an insufficient gas issue. |
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Posted: 6/7/2020 10:30:36 PM EDT
[#42]
Quote HistoryQuoted: O.K., I installed a new gas tube. (My new gas block is back ordered) I pulled the gas block and it appeared to be installed correctly, a dirty ring surrounding the gas port. So I reinstalled the gas block with the new gas tube. I fired a round with a G.I. carrier and it halfway cycled the carrier. O.K., progress! So I installed the Lightweight carrier out of my wife's AR, a 2A Armament Titanium/Aluminum hybrid carrier. IT RAN!!! It's got to be an insufficient gas issue.  From your posts, it did sound like a gas problem to me. Are you going to stick with the lightweight carrier or try messing with the gas port?
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Posted: 6/7/2020 11:10:56 PM EDT
[#43]
Quote HistoryQuoted: I'm glad that you got it figured out. From your posts, it did sound like a gas problem to me. Are you going to stick with the lightweight carrier or try messing with the gas port?Two pronged approach, I’m going to figure out what’s wrong, fix it AND install one of my spare Brownells Lightweight carriers. (1/4 of the cost of the 2A Armament) |
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Posted: 6/8/2020 4:04:56 PM EDT
[#44]
Are you still running the XP spring?
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Posted: 6/8/2020 8:44:16 PM EDT
[#45]
Quote HistoryQuoted: Are you still running the XP spring? Nope, standard spring. |
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Posted: 6/8/2020 11:55:13 PM EDT
[#46]
KAK has an adjustable buffer kit if you really want to fine tune your buffer weight.
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Posted: 6/10/2020 1:45:45 PM EDT
[#47]
Looks like you’re on the right track.
I was going to say it sounds like a short stroke issue. I’ve seen rifles with short stroking problems actually partially extract, but not far enough to eject, and then force closed on the casing. Obviously this takes some force to pull the casing out, hence your difficulty. I had a FAL years ago that was doing this. I’ve never seen a chamber issue that didn’t leave telltale signs on the casing, which you didn’t have. So that leaves a gas problem, which on an AR narrows things considerably. |
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Posted: 6/14/2020 9:37:34 PM EDT
[#48]
Well, I can tentatively report success!
I only was able to have time to fire two full magazines of 5.56 today but it was with ZERO issues. I’m currently out of steel case cheap ammo, which I figure if it runs on Wolf or Tula it will run on anything. So once I can restock on crap ammo AND if it runs on it.....FIXED! How it’s now configured... Aero non-Forward Assist upper “80%” Lower I cut out Ballistic Advantage Hanson 7.5” barrel Radian Raptor charging handle Brownells Lightweight Melonite Steel BCG Rise RA-140 drop-in trigger (I use this trigger in all of my “80%” builds) KNS Anti Walk melonited trigger pins (I use these in conjunction with the Rise trigger) Standard Carbine action spring 2.9 ounce carbine buffer The only thing I foresee doing (if it’s truly fixed) is placing the barrel on a DIET! For such a short barrel, it’s a PIG! I figure to turn it down to .550 - .625 |
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