View Full Version : Problems Getting Upper to Feed Reliably [now with pics]
I purchased a bolt and barrel from reputable manufacturer, Brand X (keeping them anonymous). I assembled an upper half with the Brand X barrel and bolt, a LMT carrier, a Troy gas block, a BCM gas tube, and an unknown brand upper receiver I had laying around. When I tried to hand cycle rounds, the rifle would fail to feed any rounds coming from the right hand side of the magazine. The bolt would fail to go into battery, leaving approximately ½ inch of casing visible in through the ejection port. The round would generally be wedged in there pretty tight. The feed ramps looked good and rounds would slide easily in and out of the chamber when manually inserted. Research indicated that it was most likely an ejector problem.
The manufacturer was contacted and he stated that the ejector was most likely the issue. The bolt was returned. The manufacturer rounded off the edge of the ejector and slightly shortened it. After installing the modified bolt, he upper was able to hand cycle reliably. Unfortunately, once at the range, the upper would fail to eject 2-3 rounds/mag.
So far I have:
-Tried extra lube
-Tried various magazines (somewhat limited on mags in this caliber, but scrounged up a few)
-Tried both LMT and Noveske lowers
-Replaced the ejector with a brand new ejector
-Replaced the extractor with a known good BCM extractor/insert
-Replaced the carrier with a known good BCM carrier
-Removed the gas tube
-Replaced the upper receiver with a known good BCM upper receiver
After doing all of this, I at varying times had the rifle failing to feed from the right side of the magazine only, failing to feed from the left side of the magazine only, and failing to feed from both sides. At no point did it feed reliably. My best result was six rounds in a row.
At this point, I’m starting the think the bolt, barrel extension, or chamber are out of spec/have a tolerance stacking issue (since I've basically replaced every other part). I just wanted to see if anyone had any more ideas before I sent the item back to the manufacturer. I have no doubt that the manufacturer will make it right, but would like to fix the issue myself, if I can. I would provide pictures, but the whole thing is currently disassembled. I can slap it together real quick if pictures are necessary.
Why are you keeping the manufacturer anonymous?
Why are you keeping the manufacturer anonymous? If it ends up being bad parts, I want to give them the chance to fix the issue before publicizing their name. I also don't want to make it look like they are sending out bad parts if that is not the case. If I end up sending the parts in, I will publicize the name as well as the resolution.
Something is out of whack- or it has been assembled wrong. The clue to me is the shenanigans that the "manufacturer" did with the ejector. I have never heard of this before and this tells me that some parts are out of spec. The ejector should have been replaced altogether.
I purchased a bolt and barrel from reputable manufacturer, Brand X (keeping them anonymous). I assembled an upper half with the Brand X barrel and bolt, a LMT carrier, a Troy gas block, a BCM gas tube, and an unknown brand upper receiver I had laying around. When I tried to hand cycle rounds, the rifle would fail to feed any rounds coming from the right hand side of the magazine. The bolt would fail to go into battery, leaving approximately ½ inch of casing visible in through the ejection port. The round would generally be wedged in there pretty tight. The feed ramps looked good and rounds would slide easily in and out of the chamber when manually inserted. Research indicated that it was most likely an ejector problem.
The manufacturer was contacted and he stated that the ejector was most likely the issue. The bolt was returned. The manufacturer rounded off the edge of the ejector and slightly shortened it. After installing the modified bolt, he upper was able to hand cycle reliably. Unfortunately, once at the range, the upper would fail to eject 2-3 rounds/mag.
So far I have:
-Tried extra lube
-Tried various magazines (somewhat limited on mags in this caliber, but scrounged up a few)
-Tried both LMT and Noveske lowers
-Replaced the ejector with a brand new ejector
-Replaced the extractor with a known good BCM extractor/insert
-Replaced the carrier with a known good BCM carrier
-Removed the gas tube
-Replaced the upper receiver with a known good BCM upper receiver
After doing all of this, I at varying times had the rifle failing to feed from the right side of the magazine only, failing to feed from the left side of the magazine only, and failing to feed from both sides. At no point did it feed reliably. My best result was six rounds in a row.
At this point, I’m starting the think the bolt, barrel extension, or chamber are out of spec/have a tolerance stacking issue (since I've basically replaced every other part). I just wanted to see if anyone had any more ideas before I sent the item back to the manufacturer. I have no doubt that the manufacturer will make it right, but would like to fix the issue myself, if I can. I would provide pictures, but the whole thing is currently disassembled. I can slap it together real quick if pictures are necessary.
Something is out of whack- or it has been assembled wrong. The clue to me is the shenanigans that the "manufacturer" did with the ejector. I have never heard of this before and this tells me that some parts are out of spec. The ejector should have been replaced altogether.
Nothing special or complicated in the assembly. Just a standard AR upper. This is probably around my 30th (+/- a few) upper assembly. I haven't screwed one up in at least the last ten or so. :D
I felt like the ejector fix was a little "bubbafied," but what do I know. My original concern was that the ejector seemed slightly too long. The shortened ejector certainly solved the feeding problem. However, both the original and the new ejector protrude past the bolt lugs by a tiny fraction. This does not seem normal. It also makes me think that the issue is with the bolt rather than the ejector, since two ejectors from two different sources fit strangely.
both the original and the new ejector protrude past the bolt lugs by a tiny fraction
*ding*ding*ding*ding*
Protruding ejector would be a bolt issue. Specifically the ejector roll pin hole is drilled too far forward.
Or, an ejector issue where the pocket on the side of the ejector that the roll pin passes through is too far rearward.
Have you tried one of the other bolts you have around that you know are good just for giggles?
Or even looked at them in comparison to the one thats acting up?
EDIT:
Picture obtained from an older thread that shows roughly where the ejector tip would normally sit.
They can be slightly forward of whats shown but never protruding past the lug face.
https://www.m4carbine.net/attachment.php?attachmentid=4861&d=1272414203
polymorpheous
04-28-12, 07:27
If it ends up being bad parts, I want to give them the chance to fix the issue before publicizing their name. I also don't want to make it look like they are sending out bad parts if that is not the case. If I end up sending the parts in, I will publicize the name as well as the resolution.
As per forum rules.
Thank you OP.
:thank_you2:
I hope you get things figured out.
*ding*ding*ding*ding*
Have you tried one of the other bolts you have around that you know are good just for giggles? Or even looked at them in comparison to the one thats acting up?
This is the only bolt I have that is not 5.56. Comparing it to some 5.56 bolts, the ejector definitely looks like it sits higher. I think I'll contact the manufacturer on Monday to see about replacing the parts. I'll update the thread with results.
What caliber is it?
6.8 SPC
Update with pictures of bolt. As you can see, the ejector appears to sit a little high, protruding beyond the face of the bolt lugs by a small amount. This is the same position the original ejector was in.
http://i694.photobucket.com/albums/vv305/mechelaar/IMG_0831.jpg
http://i694.photobucket.com/albums/vv305/mechelaar/IMG_0840.jpg
does the ejector depress fully under the bolt face? An ejector that protrudes like that will cause feeding issues.
Just a thought, but do your barrel extension and upper have M4 feed ramps. I had a Stag 6.8SPC upper, with out M4 ramps, which never reliably fed rounds in the year I owned it. Stag has just recently started adding M4 ramps to their 6.8SPC offerings, due to the many problems they had. While M4 ramps are a nice addition to a 5.56 rifle, they are pretty much a must have with the larger 6.8 rounds.
constructor
04-29-12, 11:56
does the ejector depress fully under the bolt face? An ejector that protrudes like that will cause feeding issues.
That is exactly what the thread is about. It's one of my bolts. Trying to troubleshoot a rifle second hand is not easy, he doesn't want to send the upper and mags to me to check out so he is telling me what is going on and I am trying to fix it going off of the info he is giving me. He purchased a bolt and barrel and assembled it himself so it wasn't assembled, test fired and tested for function like the uppers we build are. Before Sat there had been 1 conversation and I rounded the edge of the ejector. Microbest ejectors are machined and have flat ends unlike the MIM ejectors which are more rounded. I've had trouble in the past where the case rim was getting hung on the very edge and being a sharper edge was digging into the rim of the case instead of letting the case rim slide over the ejector. The other rifle that did it functioned fine with PRI gen 1 mags but did not with Gen II mags. The gen 1 mags have a rounded corner on the feed lips which allows the case to come up a little at a time as the case moves forward and the rim of the case comes up sooner. The newer Gen II and IIIs have a squared off feed lip that holds the rear of the case down longer and the shoulder is up in the barrel extension at the time so there is more of an angle on the case. That angle makes the top of the case rim lean back into the bolt face recess and gets hung on the ejector. Additionally if the bevel of the bolt is larger it allows the case rim to sink deeper into the recess sooner. All ejectors are not the same, some a little short some a little long, They can cause problems.
The CNCs we produce these bolts on are programmed with the same X, Y, Z and A coords. It's not like we drill the holes by hand and mess up.
The quad indexer has 4 places to machine 4 bolts at a time each collet holds the bolts and must be zeroed to tell the machine where the front end of the bolt is. The rear of the bolts touch a stop inside the collet so they go to the same spot every time. If a small chip gets between the bolt and stop it will push the bolt out changing the location of every hole.
Or the bolt stop may loosen after running thousands of bolts and move rearward changing the hole location in the opposite direction.
At this point he doesn't want to send the upper and mags in for me to troubleshoot he wants to try another bolt, it may still have issues if the mags are holding the rim of the case down when the shoulder of the case is up in the extension and leans the rim back into the bolt face but we shall see.
Trying to troubleshoot a rifle second hand is not easy.
Yes, I know. I've been doing exactly that since 1998.
diving dave
04-29-12, 12:15
To the original poster, I'd send it to Constructor and let him fix it. Since the company has been named...I have a 6.8 build that was done by him and it's been 100% reliable.
constructor
04-29-12, 15:29
*ding*ding*ding*ding*
Protruding ejector would be a bolt issue. Specifically the ejector roll pin hole is drilled too far forward.
Or, an ejector issue where the pocket on the side of the ejector that the roll pin passes through is too far rearward.
Have you tried one of the other bolts you have around that you know are good just for giggles?
Or even looked at them in comparison to the one thats acting up?
EDIT:
Picture obtained from an older thread that shows roughly where the ejector tip would normally sit.
They can be slightly forward of whats shown but never protruding past the lug face.
https://www.m4carbine.net/attachment.php?attachmentid=4861&d=1272414203
The larger dia of the bolt face exposes the ejector more on a 6.8 than a 556 and a 7.62x39 is even worse. The ejector can not be moved out because it is already very close to the outside wall of the bolt.
Look at Hornadys 6.8 brass. Their loaded ammo has a bevel on the rim of the case, the brass purchased unloaded does not. SSA does not. The 6.8 and 7.62 add a few problems that the 556 doesn't have.
Doesn't change the fact that every hole in that bolt may be forward or the 1/16" dia bit may have deflected off a chip left by the countersink. The recess may be adding to it, the mags may be adding to it.
Okay, so here's what I've got. I borrowed some mags and two known good 6.8 bolts (both different brands) from a friend. I tried out all three bolts with a variety of mags including Barrett, ASC, C Products, Bushmaster, and PRI.
-The two borrowed bolts fed 100% reliably with each type of mag. Zero feeding malfunctions.
-The ARP bolt failed to feed with every mag. It ran better with some mags than others. The Barrett failed every third round or so. The ASC failed on almost every round.
The only anomaly is that the PRI mag I used would only lock back reliably with the ARP bolt. :confused:
Trying to troubleshoot a rifle second hand is not easy, he doesn't want to send the upper and mags to me to check out so he is telling me what is going on and I am trying to fix it going off of the info he is giving me. He purchased a bolt and barrel and assembled it himself so it wasn't assembled, test fired and tested for function like the uppers we build are.
Sir, I appreciate your offer for me to send in my upper and found it to be very generous, considering you did not assemble it. I respectfully declined your offer because I believed either the bolt or the barrel extension was causing the issue. You assured me that the barrel extension was not the cause. I told you I would be happy if you let me exchange the bolt, and that I would prefer not to send in the whole upper. I am now fairly confident that the issue is, in fact, the bolt and am still interested in exchanging it. The only other possibility is that I ended up with two out of spec ejectors in a row. I've had worse luck than that in the past. I am not, however, interested in custom fit parts, including ejectors or magazines, on an AR15 platform.
Before Sat there had been 1 conversation and I rounded the edge of the ejector.
Actually, three conversations over the phone. ;)
constructor
04-30-12, 00:33
From yesterday-
"We spoke last week regarding feeding issues with my bolt/barrel combo I purchased from you. The assembled upper originally would not feed. I returned the bolt and you shortened and rounded the edge. This resolved the feeding issues, but the rifle began to fail to eject."
So is it failing to feed like you said in the forum posts or failing to eject like you said yesterday?
I'm sorry for the confusion. The upper was originally failing to feed. You recommended I try to round off the edge of the ejector. I hit it with a file, but was apparently not aggressive enough. I sent you the bolt. You rounded it further and returned the bolt to me. The bolt then fed reliably. Unfortunately it also failed to eject reliably. I spoke with you again and you suggested filing down the extractor. I replaced the extractor with a known good BCM extractor and the the rifle continued to fail to eject. I then replaced the ejector with a brand new unused ejector. The rifle now ejects, but it fails to feed again.
The upper, if assembled with the parts supplied by you (including the rounded ejector) feeds reliably, but fails to eject. The upper with the brand new ejector ejects reliably, but fails to feed (as it did with the original ejector before it was rounded). I once again apologize for the confusion.
Constructor/ARP has offered to take back the barrel/bolt and issue a refund. This thread can be locked.
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.