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Posted: 4/4/2014 7:21:34 PM EDT
So I recently built a 6.8 and am running into some problems. The rifle is not extracting the next round. The rifle cambers fine and fires. But when the bolt goes back the shell does not get extracted. This causes a double feed. So that rules out a gas issue. The other thing is when I put a round in and do not fire it everything extracts like it should when the auction is manually worked. It is a new YHM barrel and complete bolt assembly. I checked the extractor and all seems well. I took a good look at the chamber and it is smooth and clean.
So I am wondering if I have an issue of when the case is fired it expands causing it to get stuck? So like something is out of spec. or something. I have only tried 6.8 Hornady ammo. The odd part is that it cycles ammo fine when manually worked. Any help or ideas would be appreciated. 
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Posted: 4/4/2014 8:28:14 PM EDT
[#1]
Describe your gas system and recoil system please:
Gas system length, gas port diameter Recoil spring, buffer, weights/lengths, extension tube type, bolt carrier weight... |
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Posted: 4/5/2014 6:23:08 AM EDT
[#2]
Ive had similar issues with hornady in my arp barrel/bolt combo. ssa is fine. El cheapo remmy was fine too. I dunno what the deal is. I just dont use hornady ammo. I almost have enough brass to load my own so we shall see.
Pop over to 6.8 forums and ask there. |
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Posted: 4/5/2014 7:05:28 AM EDT
[#3]
I am using a mid length gas system. As for the ammo advice I will have to pick up a couple kinds and see if that works. I really do not want a rifle that is ammo sensitive.
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Posted: 4/5/2014 9:17:52 AM EDT
[#4]
Quote HistoryQuoted:
I am using a mid length gas system. As for the ammo advice I will have to pick up a couple kinds and see if that works. I really do not want a rifle that is ammo sensitive. No, what buffer? Spring? Gas Block? Who put it together? |
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Posted: 4/5/2014 10:43:26 AM EDT
[#5]
Load one round in the mag and fire it, tell us what happens.
Does it extract, not, does it attempt to extract? Does the bolt lock back on the empty mag? If you're running a superbolt from arp, it's possible to assemble the bcg with the extractor to the inside instead of the outside. I did this assembling in the dark once. If you do this it will of course attempt to eject to the inside. |
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Posted: 4/5/2014 10:44:37 AM EDT
[#6]
What do the rims look like on cases that don't extract? Are they chewed up, scarred, or just normal? That'll tell you if your extractor is trying to do its job.
Is the chamber super clean? Not just "nice and clean," but shiny clean all the way into the rifling. Do you have a chamber brush for 6.8? If not, get one and re-clean the ever lovin' snot out of the chamber manually, NOT with the brush in a drill!!! |
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Posted: 4/5/2014 10:45:41 AM EDT
[#7]
Quote HistoryQuoted:
No, what buffer? Spring? Gas Block? Who put it together? Quote HistoryQuoted:
Quoted:
I am using a mid length gas system. As for the ammo advice I will have to pick up a couple kinds and see if that works. I really do not want a rifle that is ammo sensitive. No, what buffer? Spring? Gas Block? Who put it together? What GTFoxy said, he's a good guy, knows his stuff, and's one of my buddies from 68forums, which as another poster mentioned, go there and sign up. This isn't a caliber issue though. |
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Posted: 4/5/2014 12:51:05 PM EDT
[#8]
The chamber is super clean and free of bores. E even ran a Q tip in it to see if it would catch on any little burs I couldn't see. The gas block is a YHM one. I put the rifle together myself and have built AR's in 8 calibers and have never ran into this issue before. I am using a standard carbine spring and buffer. This is my first 6.8 so if I need to upgrade the buffer or spring please let me know.
When I put one round in and fire it. It cycles fine and locks back on an empty mag. However the round is not extracted. The rounds do not show hardly and mark from the extractor trying to grab it. I checked and the extractor feels nice and strong though. It makes me wonder if the extractor spring needs an upgrade?? But when I hand cycle it the extractor if fine. I really don't think this is a gas issue at all. I am thinking an extractor or a chamber spec issue maybe? I am using a YHM barrel and complete BCG. Also i appreciate all the help on this. I think i covered all the questions. |
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Posted: 4/5/2014 7:30:12 PM EDT
[#9]
Sounds like you are dealing with a bad extractor or a tight chamber.
Did you check headspace? If it is tight it could be sticking. I would take the bolt apart, if you haven't already, & check for any goopy or reason the extractor would not work. Then check headspace while you have it apart. I would be real surprised if a YHM bolt had weak spring or some error that would cause this but...it would be better than a chamber that's too tight. Did you check the I.D. of the bolt? Maybe it is a tad on the loose side & can't grip the rim hard enough when it is cycling. Aside from Headspace & the bolt/extractor I don't know what else it may be. If it locks back but won't remove the case then only so much it can be. |
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Posted: 4/5/2014 7:44:01 PM EDT
[#10]
Had a 7.5" 223 gun that either wouldn't extract, or leave the fired case on top of the mag (was only single loading at this point since I had just built it). Added an o-ring to the extractor and that solved all my problems. Gun runs like a raped ape now.
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Posted: 4/5/2014 11:01:49 PM EDT
[#11]
Quote HistoryQuoted:
Had a 7.5" 223 gun that either wouldn't extract, or leave the fired case on top of the mag (was only single loading at this point since I had just built it). Added an o-ring to the extractor and that solved all my problems. Gun runs like a raped ape now. My question is why did you need it? OP, what length barrel do you have? Have you contacted YHM for input? |
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Posted: 4/5/2014 11:31:43 PM EDT
[#12]
Same thing was going on with my brand new 10.5" 6.8, added o ring now it runs great.
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Posted: 4/6/2014 6:28:48 AM EDT
[#13]
There are two different things going on when a case is extracted. Often the extractor is slightly opened by being pushed forward against the front edge of the extraction groove on a case, so when the bolt starts going backward the extractor has to slide back into the groove fully. The other thing is that the bolt has turned - though the case has not necessarily loosened in the chamber. So as the bolt starts moving backward there's a chance that the extractor spring isn't fast enough to catch the rim, and the case may also be stuck a little tightly as well. In the M4's evolution, the Crane O Ring was a fix for this issue: a bolt moving backward faster than the standard extractor spring could react, with hot, still-stuck brass resisting extraction.
With a 6.8, there are a couple of issues that could lead to the same sorts of things. Which standard was the chamber cut to? What brass was being used - is it slightly long, is its extraction groove "low" or "short"? Is the load "hot" for that particular barrel? Any of these could give the rifle essentially the same symptoms, and an O-ring fix could be just the ticket. |
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Posted: 4/6/2014 6:31:29 AM EDT
[#14]
had a .308 that was like that. for that gun I now resize with SB die and make sure the die is screwed all the way down to get minimum case headspace and have replaced extractor spring and added o ring and now its GTG.
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Posted: 4/6/2014 7:10:43 PM EDT
[#15]
Quote HistoryQuoted:
There are two different things going on when a case is extracted. Often the extractor is slightly opened by being pushed forward against the front edge of the extraction groove on a case, so when the bolt starts going backward the extractor has to slide back into the groove fully. The other thing is that the bolt has turned - though the case has not necessarily loosened in the chamber. So as the bolt starts moving backward there's a chance that the extractor spring isn't fast enough to catch the rim, and the case may also be stuck a little tightly as well. In the M4's evolution, the Crane O Ring was a fix for this issue: a bolt moving backward faster than the standard extractor spring could react, with hot, still-stuck brass resisting extraction. With a 6.8, there are a couple of issues that could lead to the same sorts of things. Which standard was the chamber cut to? What brass was being used - is it slightly long, is its extraction groove "low" or "short"? Is the load "hot" for that particular barrel? Any of these could give the rifle essentially the same symptoms, and an O-ring fix could be just the ticket. So the o-ring puts tension on the extractor arm behind the spring so that it can't open to much & loose grip on the base. Correct? That is fine. It still doesn't fix the actual issue. IMO, it is a bandaid remedy of the causality. Not a true removal of the issue at hand. It makes me wonder since my 6.8 has never done it & I have gone way over factory loadings. I liken this to back in the day when guys were running factory supercharger kits with little injectors. The problem was lack of fuel volume @ standard operating pressures. The "Fix"? Use an FMU to increase rail pressure certain ratios above atmospheric pressure. That worked great till pumps started failing, injectors would lock up, engines still got blown. The real fix was to tune the car with a good management system & use the appropriate injector & pumps for the application. Viola those FMU'S that were so popular in the early to late 90's are all but a fond memory of il-conceived solutions. But it sold a lot of factory SC kits... |
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Posted: 4/7/2014 4:21:23 PM EDT
[#16]
The O ring is around the spring, and it does limit free movement of the extractor. The "real" issue really is that the gun can sometimes outrun its own extractor for various reasons. With the M4 it's because of extended automatic fire and the need to keep the weapon working in combat, even with a dirty gas system, aging spring, etc., etc.
In a civilian rifle that's brand new, if an O ring is needed there is something wrong with the rifle. |
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Posted: 4/7/2014 5:04:21 PM EDT
[#17]
Quote HistoryQuoted:
The O ring is around the spring, and it does limit free movement of the extractor. The "real" issue really is that the gun can sometimes outrun its own extractor for various reasons. With the M4 it's because of extended automatic fire and the need to keep the weapon working in combat, even with a dirty gas system, aging spring, etc., etc. In a civilian rifle that's brand new, if an O ring is needed there is something wrong with the rifle. Around the spring. That is what I meant. My point exactly. If this is a new build something is not right. |
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Posted: 4/8/2014 5:51:12 AM EDT
[#18]
It is a new build. I am thinking that I will try a stronger buffer spring or heavier buffer first. I am surprised the brass does not have any gouging from the extractor grabbing and then slipping off which is odd. I do have a couple different ammo's to try coming now as well. I think the o -ring will be the last resort.
I am still suspicious that it is a chamber issue though. |
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Posted: 4/8/2014 9:31:07 AM EDT
[#19]
Strange that you don't have any pull marks at all. Remove your extractor and see if anything is holding it in the open position.
You should be getting pull marks on your brass, hard ones at that if it's slipping off. |
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Posted: 4/8/2014 9:53:06 AM EDT
[#20]
It is odd. When I hand cycle a round it extracts just fine.
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Posted: 4/8/2014 9:56:20 AM EDT
[#21]
YHM bolt.
Possible they used a 5.56 extractor and not a 6.8? |
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Posted: 4/8/2014 9:57:07 AM EDT
[#22]
Quote HistoryQuoted:
It is odd. When I hand cycle a round it extracts just fine. That's because the case is not expanded under pressure. |
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Posted: 4/8/2014 11:56:24 AM EDT
[#23]
Quote HistoryQuoted:
YHM bolt. Possible they used a 5.56 extractor and not a 6.8? Is it me or does his extractor look to be indeed hanging too far into the bolt face area? I recommended pulling the extractor & ejector apart. Still waiting on barrel info... At this point I would be on the horn ordering a set of go, no go gauge to double check things & to have some real info if a call to YHM is in order. |
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Posted: 4/8/2014 12:43:48 PM EDT
[#24]
Here's the difference in the extractor profiles.
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Posted: 4/8/2014 2:57:18 PM EDT
[#25]
I think Stag uses the same extractor on their 5.56 and 6.8 bolts. I didn't know there was a difference in the extractors in 6.8's. I believe 6.5 grendel uses a different one.
https://www.stagarms.com/bolt-rebuild-kit/ |
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Posted: 4/8/2014 3:14:43 PM EDT
[#26]
Quote HistoryQuoted:
I think Stag uses the same extractor on their 5.56 and 6.8 bolts. I didn't know there was a difference in the extractors in 6.8's. I believe 6.5 grendel uses a different one. https://www.stagarms.com/bolt-rebuild-kit/ Look at the depth of the notch http://www.midwayusa.com/product/838573/dpms-extractor-ar-15-matte http://www.midwayusa.com/product/613191/dpms-extractor-ar-15-68mm-remington-spc-matte?cm_vc=ProductFinding |
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Posted: 4/8/2014 3:23:21 PM EDT
[#27]
Edit: I was wrong. No difference in extractors. |
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Posted: 4/8/2014 3:40:11 PM EDT
[#28]
I see the difference in the notch and I would think that there should be a difference. I was going on what I have read in the past about them being the same. Here one example:
http://68forums.com/forums/showthread.php?15401-6-8-extractors |
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Posted: 4/8/2014 5:03:38 PM EDT
[#29]
I just measured some extractors & the easiest way I could see is to measure across the rim Grove to what would be the height of the groove.
My 556 extractor measures right about .060" & the 6.8 is right about .070" I'll keep measuring them but right now the grooves are the same depth & the widths are the same.. Edit: I trust H so I was not correct. Other than the above mentioned dims the extractors appear to be the same... Thanks for posting. I missed that memo. We'll see if just slowing it down helps for him. |
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Posted: 4/8/2014 6:35:28 PM EDT
[#30]
So is there any chance that someone has a set of 6.8spc GO NO-GO head spacing gauges I could borrow. I have a 5.56 set but do not plan to build any more 6.8 's. So I don't want to dump money into them. I am willing to throw in a couple thanks for the loan items when I send the gauges back.
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Posted: 4/10/2014 4:30:34 PM EDT
[#31]
Which 6.8 chamber do you have? There are several "standards" for the 6.8: SAAMI, SPC II, DMR, etc. And these are substantially different from each other. It kind of makes a difference for which headspace gauges you get.
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Posted: 4/11/2014 4:17:18 AM EDT
[#32]
I have the SPC II.
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Posted: 4/11/2014 6:41:02 AM EDT
[#33]
Quote HistoryQuoted:
Which 6.8 chamber do you have? There are several "standards" for the 6.8: SAAMI, SPC II, DMR, etc. And these are substantially different from each other. It kind of makes a difference for which headspace gauges you get. Sorry but you are wrong. All 6.8 chambers use the same headspace gauges, same reloading dies and brass. |
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Posted: 4/11/2014 7:56:10 AM EDT
[#34]
Quote HistoryAFAIK ARP uses 5.56 extractors on his 6.8 Superbolts. At least according to "H" directly. |
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Posted: 4/11/2014 8:06:55 AM EDT
[#35]
Quote HistoryQuoted:
Which 6.8 chamber do you have? There are several "standards" for the 6.8: SAAMI, SPC II, DMR, etc. And these are substantially different from each other. It kind of makes a difference for which headspace gauges you get. So are there different headspace gauges for 223 vs 5.56? Nope The different chambers for 6.8 have mostly to do with freebore to help with higher pressure just like 5.56 chambers help with higher pressures. Also the original 6.8 SAAMI'd chamber had an incorrect Cone angle which caused higher than normal pressures. So in regards to the 6.8 it's not really the chamber itself but how much extra the chamber reamer removes in the Leade area. |
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Posted: 4/11/2014 4:15:16 PM EDT
[#36]
I was misinformed. I was originally told that there was some sort of difference between the various chambers' shoulder angles... I could have misunderstood (probable) or merely heard someone talking out of his ear (also quite possible). Since I hadn't gotten into the 6.8, I haven't looked into it that much.
Plese inform me - and the OP: what are the differences between the various 6.8 chambers? |
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Posted: 4/12/2014 7:59:28 PM EDT
[#37]
Quote HistoryQuoted:
I was misinformed. I was originally told that there was some sort of difference between the various chambers' shoulder angles... I could have misunderstood (probable) or merely heard someone talking out of his ear (also quite possible). Since I hadn't gotten into the 6.8, I haven't looked into it that much. Plese inform me - and the OP: what are the differences between the various 6.8 chambers? Quote HistoryQuoted:
I was misinformed. I was originally told that there was some sort of difference between the various chambers' shoulder angles... I could have misunderstood (probable) or merely heard someone talking out of his ear (also quite possible). Since I hadn't gotten into the 6.8, I haven't looked into it that much. Plese inform me - and the OP: what are the differences between the various 6.8 chambers? Taken from ARP FAQ What is the difference between our 6.8 x 43 and the SPCII?
Both chambers will allow the use of any 6.8 ammo including SSA Tac loads and Wilson Combats SPCII loads. The ARP designed chamber uses a bullet diameter leade which aligns the bullet in the bore better than the SPC II. Our chamber was designed to fix a cone angle error in the original SPCII chamber in 2007. Both chambers use the same brass and reloading dies. The new SPCII(as of 6/2010) has .114" freebore where the 6.8x43 has a .095" long freebore so it doesn't have as much jump to the lands as the new SPCII and can be more accurate. |
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Posted: 4/13/2014 2:07:38 PM EDT
[#38]
Quote HistoryQuote HistoryQuoted:
Quoted:
I was misinformed. I was originally told that there was some sort of difference between the various chambers' shoulder angles... I could have misunderstood (probable) or merely heard someone talking out of his ear (also quite possible). Since I hadn't gotten into the 6.8, I haven't looked into it that much. Plese inform me - and the OP: what are the differences between the various 6.8 chambers? Taken from ARP FAQ What is the difference between our 6.8 x 43 and the SPCII?
Both chambers will allow the use of any 6.8 ammo including SSA Tac loads and Wilson Combats SPCII loads. The ARP designed chamber uses a bullet diameter leade which aligns the bullet in the bore better than the SPC II. Our chamber was designed to fix a cone angle error in the original SPCII chamber in 2007. Both chambers use the same brass and reloading dies. The new SPCII(as of 6/2010) has .114" freebore where the 6.8x43 has a .095" long freebore so it doesn't have as much jump to the lands as the new SPCII and can be more accurate. |
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Posted: 4/13/2014 6:12:04 PM EDT
[#39]
Quote HistoryQuoted:
I see. My information made it sound like the shoulder was different, where instead it's a difference in the angle of the leade, much like the difference between .223 SAAMI and 5.56mm NATO chambers. Thanks. Quote HistoryQuoted:
Quoted:
Quoted:
I was misinformed. I was originally told that there was some sort of difference between the various chambers' shoulder angles... I could have misunderstood (probable) or merely heard someone talking out of his ear (also quite possible). Since I hadn't gotten into the 6.8, I haven't looked into it that much. Plese inform me - and the OP: what are the differences between the various 6.8 chambers? Taken from ARP FAQ What is the difference between our 6.8 x 43 and the SPCII?
Both chambers will allow the use of any 6.8 ammo including SSA Tac loads and Wilson Combats SPCII loads. The ARP designed chamber uses a bullet diameter leade which aligns the bullet in the bore better than the SPC II. Our chamber was designed to fix a cone angle error in the original SPCII chamber in 2007. Both chambers use the same brass and reloading dies. The new SPCII(as of 6/2010) has .114" freebore where the 6.8x43 has a .095" long freebore so it doesn't have as much jump to the lands as the new SPCII and can be more accurate. Aside from chambering, the ARP use of 5 groove rifling plays an important role in terms of pressure management. Every little bit helps in certain circumstances. |
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Posted: 4/19/2014 4:43:10 PM EDT
[#40]
Well I just wanted to thank everyone for the ideas. Someone mentioned the buffer and buffer spring maybe the issue. So I replaced the buffer spring with a little bit more stout one and that fixed it. The rifle runs great now. Thanks again.
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