Gunsmithing AR10 Feeding Issue

[jda2631]

I built a large frame AR that is giving me some issues. It is SLR upper receiver, proof 6.5 creed carbon barrel, JP H2 SCS, and Rubber City Armory titanium BCG with their bolt also.

100% of the time if I have the BCG locked open, insert loaded magazine, then release the bolt to chamber a round. It puts a round into the chamber but the extractor doesn't grab it. It won't fire. I have to "charge" the bolt and it will "grab" the round that is already in the chamber when the BCG goes into battery. But now the same live round is in the chamber, extractor has the round also, but the bcg is locked in battery, I can't easily charge the rifle to unchamber the round. I have to mortar the rifle (hold a hand on the charging handle, and hit the butt of the rifle on a table for leverage to get the bcg to unchamber the round)

If I start with bolt closed, insert magazine, then charge rifle this doesn't happen every time, but still happens occasionally.

Any idea what is going on? Or how to diagnose what is going on?

 

[loveha]

Tight specs? Rough locking lugs? Did you try a go gauge?
Other thought is not enough ass in the BCG but I doubt it with the H2 buffer.

 

[jda2631]

The chamber is a little tight but I just chalk that up to proof having a really tight spec'd chamber. The lugs look and feel smooth to my hands? I don't have a go/no go gauge, I may snag one. I also may snag the spring pack for the SCS, see if there is a stiffer spring and if that will help. But it's a titanium BCG, so it's light, and the AR10 H2 SCS with whatever spring comes on it.

 

[2aBaC̶a̶]

Check for 2 o rings on the extractor.

 

[whatsupdoc]

Are You using reloads?

 

[jda2631]

Are You using reloads?

Yes, but bought some factory hornady 140 eld-m's, did the same thing.

Check for 2 o rings on the extractor.

Ok will do.

 

[whatsupdoc]

Separate the upper from the lower, remove the BCG and drop a empty case in the chamber. Does it easily go into the chamber ? Is it easily removed from the chamber using a pick of some kind. If it goes in and out without issue you may have some kind of interference between the barrel extension and the extractor.

 

[Hellbender]

Why did you buy a titanium BCG??? Then have an H2 buffer??? Remove weight, then just add it back? Just curious....

Remove the BCG....an unfired, factory round should drop COMPLETELY into the chamber with the gun pointed down, if you have to push it in all the way, the chamber is too tight, send the bbl back and get another or have the chamber reamed properly.

With the lightweight BCG, combined with a 6.5 Creed, this gun will have to have everything just right to work reliably.

Chamber a round from the mag, then look at the bullet noses carefully, if the noses are getting dinged on the way in (Creeds bullet noses usually hit the barrel right below the chamber opening upon feeding), this can suck up energy required to completely close the bolt. You can tune the mags to mitigate this somewhat.

 

[Lawless]

Sounds like a chamber or misalignment issue.

 

[2aBaC̶a̶]

@jda2631 What's the word? Figure it out?

 

[ajwcotton]

I've had 2 proof 6.5 barrels that were .005 to .007 to tight on headspace. Sent them back to proof. Proof said they were in spec and sent them back. They were magically fixed when they came back.

 

[jda2631]

I was busy with family stuff all weekend, going to work on it tonight and see what I can come up with.

 

[hunter8793]

Any update?

 

[jda2631]

I took out BCG, had a factory hornady 140 eld-m, gun standing up on the barrel, dropped the round in. With no force but gravity, it stopped probably 1/8" short of being fully into the chamber. I had to push it fully into the chamber with my finger, it didn't take much effort, but gravity wasn't enough. And it took constant force from my finger the whole way pushing it in, not like i tapped it and it fell the rest of the way in. I fully cleaned the barrel and chamber before doing this also. I guess I should contact proof?

One question though is what causes the bolt to get locked into battery? If there is no round in the chamber, I can fully cycle the BCG with no issue, locks into battery, unlocks with no issue. But with a round in the chamber, I have to mortar it a few times before I can get the bolt to unlock and unchamber the live round. If I fire the round, it will eject fine.

 

[Hellbender]

AR's have very little bolt UNcamming force if just manually operated.
I'd contact Proof, sounds like your chamber is way too tight (unless you somehow got an oversized batch of Hornady's).

 

[jda2631]

AR's have very little bolt UNcamming force if just manually operated.
I'd contact Proof, sounds like your chamber is way too tight (unless you somehow got an oversized batch of Hornady's).

I tried a few, then I had a bag of sized brass, same thing.

 

[2aBaC̶a̶]

I took out BCG, had a factory hornady 140 eld-m, gun standing up on the barrel, dropped the round in. With no force but gravity, it stopped probably 1/8" short of being fully into the chamber. I had to push it fully into the chamber with my finger, it didn't take much effort, but gravity wasn't enough. And it took constant force from my finger the whole way pushing it in, not like i tapped it and it fell the rest of the way in. I fully cleaned the barrel and chamber before doing this also. I guess I should contact proof?

One question though is what causes the bolt to get locked into battery? If there is no round in the chamber, I can fully cycle the BCG with no issue, locks into battery, unlocks with no issue. But with a round in the chamber, I have to mortar it a few times before I can get the bolt to unlock and unchamber the live round. If I fire the round, it will eject fine.

The carrier sliding forward after the bolt stops on the barrel forces the cam pin to the side thus rotating the bolt.

Take your BCG out and push it on the palm of your hand.

Have you tried taking the bolt out of the BCG along with the extractor out of the bolt and putting a rounding the end of the bolt and fit it into the chamber?

Are there any marks on the brass that you get to chamber?

I feel like were overdue for some pics... of everything.

 

[Killswitch Engage]

sounds like you don't have a firm understanding of how an AR type platform rifle functions.

you really need to drop a headspace gauge into the chamber and see what you have. i would strip the bolt of the ejector and extractor and see if it will rotate into battery on a go gauge. if it will not you know your issue. you can then take new ammunition and try the same thing. if the bolt does not easily rotate into battery then i would then suspect a chamber diameter that is on the tight side from reamer wear possibly.

 

[Hellbender]

sounds like you don't have a firm understanding of how an AR type platform rifle functions.

you really need to drop a headspace gauge into the chamber and see what you have. i would strip the bolt of the ejector and extractor and see if it will rotate into battery on a go gauge. if it will not you know your issue. you can then take new ammunition and try the same thing. if the bolt does not easily rotate into battery then i would then suspect a chamber diameter that is on the tight side from reamer wear possibly.

Even if the headspace is OK, if the chamber is too tight (as his apparently is), the gun will not work properly. So any way around it, he needs to get the chamber fixed.

A headspace guage only measures from the face of the bolt to the shoulder datum line, NOT the "tightness" of the chamber.

 

[whatsupdoc]

I tried a few, then I had a bag of sized brass, same thing.

Forget Sized Brass, USE NEW BRASS. Brass fired from another rifle with a loose chamber will always give issues if you happen to ger a chamber on the tight side. A normal full length sizing die does not squeeze the bottom end of the case.

 

[2aBaC̶a̶]

Factory ammo is usually saami spec.

Still think he might have 2 O rings on the extractor spring. Take one off and see what happens.

Had the same issue and it drove me nuts.

 

[Killswitch Engage]

Even if the headspace is OK, if the chamber is too tight (as his apparently is), the gun will not work properly. So any way around it, he needs to get the chamber fixed.

A headspace guage only measures from the face of the bolt to the shoulder datum line, NOT the "tightness" of the chamber.

apparently you didn’t bother to read all of what I wrote...

 

[jda2631]

Check for 2 o rings on the extractor.

I apologize for slow responses, work and holidays have had me pretty tied up.

I took the bolt apart, and there were 2 o-rings on the extractor spring. Removing one has helped, thank you for that info. I wouldn't have thought to look at that and wouldn't have found it for while, until I broke it down completely for cleaning. But this has gotten rid of the issue where it wouldn't fire when a loaded mag was inserted on open BCG, BCG was dropped, then it wouldn't fire.

It's still not running well. As stated above, I am running an SLR AGB, so it's click/detent adjustable. It will run well for a few rounds then it will not fully eject before loading the next round like it's undergassed, so I will open the gas by 1 or 2 clicks (not a big adjustment) and it will rip the rim off the fired round and not cycle.

(edit to add: I tested this after removing the 2nd extractor spring O-ring with reloaded 130 gr Berger Hybrids as well as factory 140 eld-m's)

Should I try one of the stiffer springs on the JP SCS (it's the standard H2 SCS from JP right now) to slow down the BCG? The chamber is definitely a little tight, I haven't contacted proof yet but think that I should do that as well?

I've never had this many issues with an AR and it's driving me crazy.

 

[gnochi]

I apologize for slow responses, work and holidays have had me pretty tied up.

I took the bolt apart, and there were 2 o-rings on the extractor spring. Removing one has helped, thank you for that info. I wouldn't have thought to look at that and wouldn't have found it for while, until I broke it down completely for cleaning. But this has gotten rid of the issue where it wouldn't fire when a loaded mag was inserted on open BCG, BCG was dropped, then it wouldn't fire.

It's still not running well. As stated above, I am running an SLR AGB, so it's click/detent adjustable. It will run well for a few rounds then it will not fully eject before loading the next round like it's undergassed, so I will open the gas by 1 or 2 clicks (not a big adjustment) and it will rip the rim off the fired round and not cycle.

(edit to add: I tested this after removing the 2nd extractor spring O-ring with reloaded 130 gr Berger Hybrids as well as factory 140 eld-m's)

Should I try one of the stiffer springs on the JP SCS (it's the standard H2 SCS from JP right now) to slow down the BCG? The chamber is definitely a little tight, I haven't contacted proof yet but think that I should do that as well?

I've never had this many issues with an AR and it's driving me crazy.

I’d contact Proof before doing anything else, aside from checking whether a go gauge works with your bolt and barrel if you haven’t already.

 

[2aBaC̶a̶]

Will factory rounds chamber and extract easily if not fired?

Im thinking the BCG is too light and trying to extract the round while it's still pressurized and gripping the chamber.

Other than trying a different BCG, would try adding tungsten weights to the JP SCS to slow the cycle process.

If you have other springs it wouldnt hurt to try them but I dont think it will help. They are mostly for mitigating travel and pushing the buffer back into battery.

 

[2aBaC̶a̶]

Does your RCA Titanium BCG have an adjustable gas key?