AR feed problem

[Viperdoc]

Working up loads for my AR. Last year added a Fulton Armory side cocking upper. Checked length to lands, etc, but never made a dummy round to confirm feeding.

The bolt will close on its own, but even with a sized empty case the bolt will stop short and not close. With a good push on the bolt it will close on an empty case, maybe. empty, the bolt closes fine. the gun and chamber are clean.

Any ideas?

 

[Minesweeper3433]

I had a problem with a LW barrel for my AR15 doing this and I just adjusted my sizing dies to go a little further. Fixed it for me. If you have access to a good set of head-space gauges check to make sure it is not at minimum with your barrel/extension/bolt setup.

 

[Viperdoc]

First thing I checked was the go, no-go gauges, and the chamber reaming seemed OK. It was a Krieger 1/9 barrel with a custom reamer. Changed barrels and upper receivers, and it seems like the problem lies with Fulton side cocking upper and bolt combination. Lubed everything, but it still takes a little push at the back of the BCG to close the bolt when there's either an empty (but FL resized) brass or dummy cartridge in place. Without brass or cartridge in place, the bolt closes OK.

This was all done with the upper receiver detached from the lower.

Could the bolt be binding somehow in the bolt carrier? Any other ideas?

 

[fdshuster]

Does it chamber factory ammo?

 

[jonbearman]

What about a stuck or sticking ejector pin.Just a thought.Do you use a small base die?

 

[Viperdoc]

Great idea to try factory ammo- are you suggesting that my reloads might be somehow inadequate? Never happened before!! (just kidding of course)

The brass is FL resized Lapua 223 brass in a Redding FL type S die. The reamer was a SAAMI for the case, but zero throat to try to get the bullets close to the lands from the mag.

It seems like the ejector works- if I push the bolt closed, and then pull it back with the cocking handle it will eject the case normally. Is there another way to test this?

I am thinking that having the case in the bolt face, something is keeping the bolt from rotating and locking in place. Perhaps taking the bolt out of the BCG, disassemble, and really lubing it well might help? Or, is this a sign of a stuck ejector?

I really prefer the heavier M-16 bolt compared to the lightweight AR bolt, but until I get a heavy BCG drilled and tapped for the side cocking handle, I am stuck.

I should mention that I have been also running with the CWS weights in the bolt, but do not see how this would alter the locking/closing functions, I hope.

Thanks.

 

[jonbearman]

Doc have you measured a few loaded rounds form the shoulder to the base using the hornady tool or equivalant. It is usually a slight bulge at the base which a small base die would fix or the shoulder isnt bumped quite enough or the side bolt handle binds and slows the carrier down just enough to not go to battery.

 

[Beau]

You need to take another thou or 2 off the case's headspace. Size it down a little tighter.

 

[Minesweeper3433]

First thing I checked was the go, no-go gauges, and the chamber reaming seemed OK. It was a Krieger 1/9 barrel with a custom reamer. Changed barrels and upper receivers, and it seems like the problem lies with Fulton side cocking upper and bolt combination. Lubed everything, but it still takes a little push at the back of the BCG to close the bolt when there's either an empty (but FL resized) brass or dummy cartridge in place. Without brass or cartridge in place, the bolt closes OK.

This was all done with the upper receiver detached from the lower.

Could the bolt be binding somehow in the bolt carrier? Any other ideas?

If it only takes slight finger pressure to close the bolt when upper is separated from the lower than you are fine. It is when you have to use the forward assist after spring assisted cycle to chamber a round that you should worry. I fixed over a dozen M4s today at work and when loading dummy rounds for cycle testing we never ride the bolt forward we pull back and let fly. Your rifle will never chamber a round without the buffer and spring throwing your bolt forward so worrying about a little finger pressure needed is nothing as long as it does close. If anything you have a good minimum spec chamber and your brass won't get worked as much as some AR's can.

 

[Viperdoc]

With the Fulton Armory side cocking upper and bcg, the rifle would not go into battery and lock with a fl resized case or a reload. With the upper detached (no spring) it would lock up, but still with some significant finger pressure on the back of the bcg.

Took the barrel off and put it on another standard upper, and it functioned fine, with no FTF in around 250 shots.

My dies set the shoulder back around 0.003 as I recall, and the chamber is shiny clean.

Seems to me the problem is with the bcg binding in the upper or the bolt binding in the bcg , but only when there's a case. Will dissassemble the bolt and clean and lube.

Will report back.

Thanks for all the great ideas.

 

[Viperdoc]

My thought process was to try to Isolate the problem. With the same ammo and barrel, but a different upper and bcg, there were no problems at all. This points toward something in the side cocking upper.

I could try a different bolt and bcg to see if it locks up easily, which would then point toward the modified bcg in the side cocker.

Is this logical?

 

[jhord]

I'd guess it's the combination of your Krieger barrel and the Fulton bolt head, they aren't playing nice. (if I am reading things right) If the function is ok with a different BCG then the headspace is too tight on the combo you want to run. Try swapping bolt heads, or adjusting your die tighter. I have a Criterion/Fulton barrel on my service rifle and it has a pretty tight chamber. I was having much the same problem, a switch to a small base die, snugged down tight makes things function fine. My base to shoulder dimension is .004" tighter on my Criterion/Fulton barrel than it is on my RRA barrel.

Thinking on this a little more, I suppose it could also be a stiff extractor. Do you hear a click when you bump the BCG forward? Could be the extractor riding up over the case rim. Once you have a round slammed home, does it eject easily or is it stuck? If it is stuck, then you have a headspace issue.

 

[Jager247]

i have had this problem too. the problem was the dies were seating the should back just enough to not allow the bolt to fully close. just looking at the case i didnt see anything wrong until i looked closer. Once i adjusted the dies, i never had a problem again.

 

[Killshot]

Q: Are you closing the bolt carrier by hand (you mention the Upper is detached several times so I take it the Buffer Spring isn't seating the carrier?) or by the Charging Handle (pull back and let it fly as minesweeper mentioned) method?

If it is the former, you may not even have a problem. If the latter I'd bet that it's the barrel extension not jiving with the bolt lugs.

 

[rcw3]

You need to take another thou or 2 off the case's headspace. Size it down a little tighter.

9 times out of 10 this is the cause of what Viperdoc is seeing. If the case is too big for the chamber, it's not going to fit and the bolt won't close - it's that simple!

Presumably you are full length sizing (not neck sizing which is not appropriate for an AR-15).

Robert

 

[Beau]

My thought process was to try to Isolate the problem. With the same ammo and barrel, but a different upper and bcg, there were no problems at all. This points toward something in the side cocking upper.

I could try a different bolt and bcg to see if it locks up easily, which would then point toward the modified bcg in the side cocker.

Is this logical?

No.
The 2 chambers are different. This one is tighter. Size the cases down a little more before you go to anymore lengths.
You'll know when the cases are sufficiently sized when they chamber and eject freely.

You pull 2 random AR bolts out of a bin and there likely won't be even a thou difference between the 2 anyway.

 

[kentuckytroutbum]

Q: Are you closing the bolt carrier by hand (you mention the Upper is detached several times so I take it the Buffer Spring isn't seating the carrier?) or by the Charging Handle (pull back and let it fly as minesweeper mentioned) method?

If it is the former, you may not even have a problem. If the latter I'd bet that it's the barrel extension not jiving with the bolt lugs.

I had a similar problem with my 6.5 Grendel that was custom built. Long story short, the bolt from AA was one of a batch of 1200 +/- bolts that were out of spec, and the lugs were hitting the barrel extension, and slowing the bolt down to the point that the bolt failed to lock up, or failed to fire. The gunsmith that built the barrel, replaced the bolt at no charge, and the problems went away. Check the sides of the lugs, and see if there is unusual wear in that area. It only takes one bad lug to slow down the bolt.

While you're at it, check the cam pin, and the hole in the bolt carrier for damage or carbon build up. Also, check for carbon at the bottom of the bolt recess in the carrier.

 

[jonbearman]

Is this situation resolved Viperdoc or what.I am anxious to see what the culprit was.

 

[Viperdoc]

Yesterday, I tried a different bolt and BCG, but still see the same thing- the bolt will not lock up. The barrel is one that I have use before on different uppers, and is a Krieger Varmatch. With a different Krieger Varmatch saw the same thing happen.

So, with two different barrels and two different bolts, the problem has to lie with the Fulton Armory side cocking upper somehow. In this case the barrels were simply placed in the upper, without the locknut or gas tube, but even then it would not lock up.

Yet, without a round in the chamber, both bolts would easily lock up with a little finger pressure. With a dummy round, it would not fully chamber or lock up, with either of two barrels or either of two bolts.

The rounds have a shoulder bump of around 0.003- 0.005 (I forget exactly), and have functioned fine with these same barrels in a different upper.

With the Fulton upper, the go gauge would not chamber and lock up, and certainly not the no-go.

So, it looks like something with the upper receiver from Fulton Armory. Could there be some sort of machining or alighment issue that prevents the BCG from fully chambering? I have not contacted them as of yet.

 

[rcw3]

Funny - - if I had your upper in hand it would probably take me all of about 10 seconds to determine the issue, but over the internet on a forum it's about impossible to determine if it's an issue with the upper or an ammo issue or something else.

My bet is still it's and ammo head space reloading issue (not enough shoulder bump).

Robert