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Posted: 5/5/2020 12:34:00 AM EDT
[#1]
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Posted: 5/5/2020 12:37:54 AM EDT
[#2]
The malfunction pictured is a bolt-over-base malfunction.
Either you're short-stroking or you have a magazine seating or presentation issue. Short stroking could come from undergassing or some other issues with the buffer and action spring, but would mean the bolt comes back for enough for the empty cartridge to get out of the ejection port, but not far enough to clear the back of the magazine and let a new round present itself for feeding. If magazine seating or presentation issue, then the round is hanging up at the back in the magazine, so the bolt slides over the rim and jams up in the middle of half-presented cartridge instead of stripping and feeding it. |
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Posted: 5/5/2020 12:41:15 AM EDT
[#3]
Quote HistoryQuoted: The malfunction pictured is a bolt-over-base malfunction. Either you're short-stroking or you have a magazine seating or presentation issue. Short stroking could come from undergassing or some other issues with the buffer and action spring, but would mean the bolt comes back for enough for the empty cartridge to get out of the ejection port, but not far enough to clear the back of the magazine and let a new round present itself for feeding. If magazine seating or presentation issue, then the round is hanging up at the back in the magazine, so the bolt slides over the rim and jams up in the middle of half-presented cartridge instead of stripping and feeding it. Start with a single round in the mag, fire it and make sure it locks back on empty. That will tell you immediately if the bolt is short stroking. If it is, load a few rounds into the mag and then using your thumbnail to slid the rounds out the top. It should be smooth and easy. If it is, then look at the way the mag is presenting. Try a different one. |
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Posted: 5/5/2020 12:45:53 AM EDT
[#4]
Could this be caused by using an ar15 buffer tube? I used the buffer weight and spring for a .308 but the tube is from an ar15.
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Posted: 5/5/2020 12:47:23 AM EDT
[#5]
The bolt is not locking back after last round. Forgot to mention that.
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Posted: 5/5/2020 12:57:09 AM EDT
[#6]
Buffer tubes are supposed to be the same. If it's not locking back, then it's likely undergassed or has some sort of extra friction impeding free travel of the bolt carrier.
Does it lock back manually? |
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Posted: 5/5/2020 1:06:17 AM EDT
[#7]
Quote HistoryQuoted: The bolt is not locking back after last round. Forgot to mention that. |
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Posted: 5/5/2020 8:51:06 AM EDT
[#8]
If you assembled the upper and you don’t have a pinned fsb, remove your gas block and make sure the port is clear of any obstruction. Use a pencil to mark the top center of the barrel and gas block to ensure it is aligned properly. If that all checks out move on to your buffer assembly. Make sure you are using the correct buffer and spring for your rifle. Armalite and DPMS buffer dimensions are different in relation to the length of your bolt carrier.
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Posted: 5/5/2020 9:45:06 AM EDT
[#9]
Quote HistoryOriginally Posted By Circuits: Buffer tubes are supposed to be the same. If it's not locking back, then it's likely undergassed or has some sort of extra friction impeding free travel of the bolt carrier. Does it lock back manually? Yes, it will lock back manually |
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Posted: 5/5/2020 9:45:50 AM EDT
[#10]
Quote HistoryOriginally Posted By Powder_Burns: If you assembled the upper and you don’t have a pinned fsb, remove your gas block and make sure the port is clear of any obstruction. Use a pencil to mark the top center of the barrel and gas block to ensure it is aligned properly. If that all checks out move on to your buffer assembly. Make sure you are using the correct buffer and spring for your rifle. Armalite and DPMS buffer dimensions are different in relation to the length of your bolt carrier. I didn't assemble the upper. I bought a complete, assembled upper. The wrong buffer and spring is a possibility but I don't think I have any Armalite parts in it. When I first started this build (my first ar10) I didn't realize how different it is from an ar15. |
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Posted: 5/5/2020 9:46:57 AM EDT
[#11]
Quote HistoryOriginally Posted By AZNetEng: Sounds like you should start with the gas system. Make sure the key is tight and staked, the alignment from tube to key is good also. Might be an out of spec port or the block is misaligned on the barrel. Today I can get it on the bench and start checking this out. |
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Posted: 5/5/2020 9:54:31 AM EDT
[#12]
I also forgot to mention that it's kind of hard to pull back the charging handle. Since this is the first ar10 I've ever fired, I don't know if that's normal or not.
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Posted: 5/5/2020 1:24:11 PM EDT
[#13]
Topic Moved
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Posted: 5/5/2020 3:00:50 PM EDT
[#14]
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Posted: 5/5/2020 4:04:33 PM EDT
[#15]
Can you get access to the gas block? Are you able to verify it is reasonably centered over the gas port in the barrel?
Are you able to isolate the drag you feel that is abnormal in the bolt carrier travel? |
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Posted: 5/5/2020 8:22:02 PM EDT
[#16]
Here's a pic of the gas block. I don't see anything wrong with it but then again I am a novice at this.
 Attached File |
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Posted: 5/5/2020 8:39:54 PM EDT
[#17]
Quote HistoryOriginally Posted By GlockWrench: Can you get access to the gas block? Are you able to verify it is reasonably centered over the gas port in the barrel? Are you able to isolate the drag you feel that is abnormal in the bolt carrier travel? I'm not able to isolate any drag in the bcg. I don't know what 'normal' drag is. When I pull back the charging handle it's hard enough that I have to hold the gun vise with my other hand or it slides on the workbench. If I pull the take down pin and tilt the upper so the bcg isn't affected by the buffer spring, the bcg slides nice and easy. |
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Posted: 5/5/2020 8:43:45 PM EDT
[#18]
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Posted: 5/5/2020 8:48:17 PM EDT
[#19]
Do you have a regular AR 15 carbine buffer spring laying around? Try that.
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Posted: 5/5/2020 9:59:44 PM EDT
[#20]
Yes, I do. I won't be able to test it for a few days though. Same buffer but ar15 spring?
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Posted: 5/5/2020 10:14:37 PM EDT
[#21]
It shouldn't be difficult to pull the charging handle. I generally pull mine with one finger weak hand. Good info that it is hard to pull back. Definitely swap spring and check the charging again. Compare the spring you take out with what you swap. Post a pic if you can.
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Posted: 5/5/2020 10:15:17 PM EDT
[#22]
Quote HistoryQuoted: Yes, I do. I won't be able to test it for a few days though. Same buffer but ar15 spring? |
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Posted: 5/5/2020 10:42:58 PM EDT
[#23]
OK, I put in an ar15 spring but used the same buffer. CH pulls back much easier. Here's a pic of the two springs. The one on the left is the one I took out and the rt one is the ar15 spring.
 Attached File |
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Posted: 5/5/2020 10:50:04 PM EDT
[#24]
I think I might be able to test it tomorrow. I hope so. It feels 'right' now that I've swapped out the springs but I don't understand why the ar15 spring would be the right one and the 308 spring wouldn't work.
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Posted: 5/5/2020 11:03:07 PM EDT
[#25]
If your buffer spring came from Aero, sounds like the same problem I had. Not sure if an AR15 spring will fix it but worth a shot. I bought a JP polished and tuned AR10 spring and it instantly solved my issue. Good luck!
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Posted: 5/5/2020 11:23:14 PM EDT
[#26]
Quote HistoryOriginally Posted By RibSpreader: If your buffer spring came from Aero, sounds like the same problem I had. Not sure if an AR15 spring will fix it but worth a shot. I bought a JP polished and tuned AR10 spring and it instantly solved my issue. Good luck! Thanks. If the ar spring doesn't solve my problem I'll do the same. |
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Posted: 5/6/2020 9:09:50 AM EDT
[#27]
Unless you want to pull off the gas block and re-alaign / torque screws, field strip the upper, eyeball down the barrel from the muzzle to the gas tube hole in the upper and verify the top dead center of the gas block is roughly 12 o'clock or in line with the gas tube hole in the upper.
if you have an air compressor and blowgun you can check for free flow of gas by plugging the chamber with a fired case and sealing the muzzle while shooting air down the barrel to listen for any volume differences - this is more helpful if you are repositioning the gas block. With the lower separated from the upper, use the bolt carrier or some other tool to compress the buffer to feel if there is any grinding or binding as opposed to just spring tension. |
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Posted: 5/6/2020 9:33:35 PM EDT
[#28]
Tried it out today and it's probably worse with the 223 spring. The bolt doesn't want to slam home at all unless there are no shells involved. With no mag in place and I pull back the CH and let it go and it seems like it's ok but if I put a loaded mag in there it's trouble. Doesn't want to pick up the round. It did a couple times but mostly not. I did as someone suggested earlier and tried to just push a round out of the mag with my finger and it was hanging up. It starts to slide ok but then once it's past the bullet, the edge of the case is catching on the mag. It's a Stoner metal 5 rd mag. So that mag may be junk but I don't think that's the only problem. I'm ashamed to say that's the only mag I had with me.
 I have Pmag but it wasn't in the gun case like I though it was. So here's a pic of what happens when I tried to push a round out of the mag with my finger.  Attached File |
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Posted: 5/6/2020 11:41:07 PM EDT
[#29]
I just tried the finger push test with the Pmag and the rounds slid out ok. I put the 308 buffer spring back in and everything seems like it's ok however I didn't try it with a loaded mag. The bolt will lock back manually with the Pmag in place.
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Posted: 5/7/2020 10:16:35 PM EDT
[#30]
Did a little Dremel work on the Pmag. The rounds now slide off easier so I'm hoping that helps. If it ever quits snowing I'll go test it out tomorrow.
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Posted: 5/8/2020 12:00:02 PM EDT
[#31]
The metal mag looks like the case mouth is catching on the front lip of the mag.
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Posted: 5/8/2020 3:41:28 PM EDT
[#32]
Exactly. It was also doing it on the Pmag but not as bad. So I dremeled the Pmag but can't do a good function test until the damn snow quits and it warms up a bit. I did put a loaded pmag in the gun and when I pulled back the ch and let it go, it did chamber a round but I don't know if it will after I fire a round.
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Posted: 5/9/2020 2:44:49 PM EDT
[#33]
*UPDATE*
Got out to do some testing. SUCCESS!!!! Using the dremel on the pmag has apparently solved the problem. I only took a 20 rd box of shells with me because I figured it would either work or it wouldn't and I'd know quickly. I fired off the entire box without one ftf. I'll post a pic of the mag as soon as I finish eating (I'm starving right now) VERY HAPPY!!!! |
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Posted: 5/9/2020 5:13:40 PM EDT
[#34]
Here's a few pics of where I dremeled. Since it worked on the pmag, I also dremeled the metal Stoner mag but haven't tested it other than just racking shells through with the CH and it worked fine that way. One of these days I'll try it out while actually shooting.
I highlighted the area I dremeled because I'm sure the work is so good it looks like factory and you wouldn't be able to tell where I did it. lol. Also ignore the gouge in the follower. It jumped in front of the dremel tool when I wasn't looking.  Attached File Attached File Attached File |
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