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Bolt getting stuck in battery

wyld3man

wyld3man

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Full Member
Minuteman
Aug 18, 2017
368
281
FL
#1
I am having issues with a new AR 10 style rifle, it is a brand new build and was never shot before.

Specs:
16” .308 win X Caliber barrel, rifle length gas
Mega Maten upper/ lower combo cerakoted burnt bronze
Jp adjustable gas block
Jp BCG
Jp silent captured spring
PWS advanced buffer tube
M118 LR ammo


Observations:
Rifle will manually cycle through a magazine smoothly (not firing)
When firing the bolt will get stuck in the chamber, in order to eject the casing I will have to grab the charging handle and bump the buttstock to dislodge it
If I adjust the gas block and open it all the way up it will cycle, as soon as I begin to close the gas off it gets stuck.
No abnormal marks on the casings
I tried a different complete JP BCG, didn’t change anything
Rifle was lubed and is clean

My thoughts:
Issue with the chamber
Issue with the buffer tube
Ammo, maybe try .308 instead of 7.62

I do have another similar build, I may try swapping out upper and lowers to see what happens

Any ideas?
 
#2
To tune the gas block.

01 - Close gas block
02 - Put one round in magazine
03 - Lock bolt to rear
04 - Insert magazine
05 - Let bolt go forward
06 - Fire one round (in safe direction)
07 - If bolt not locked to rear, open gas block a slight bit more
08 - Repeat 02 thru 07 until bolt locks to the rear
09 - Let weapon cool
10 - Fire 10 rds quickly to see if there are any issues
11 - Use the suppressor that you would normally use, if you would normally use one.

==
So that would tune the gas block. If you get thru that, with no issues, you have tuned the gas block and can rule that out.

==
I have had "bolt locks in chamber before ejecting round" symptoms on multiple guns and there were multiple causes.
Among the causes:
01 - Dirty Chamber
02 - Gas block not tuned
03 - Brass flakes up in ejector port
04 - Chamber very "tight" relative to the brass size (Chamber reamed to min SAAMI spec, brass sized to max SAMMI spec)

Those are the ones I remember.

Since gun is new 01 and 03 are unlikely so I would try 02 first.
04 was a savage rifle and you don't have a savage, so 04 unlikely also ...

==
And yes, swapping out parts with similar builds is engineering 101 method to localize issue.
 
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#3
I don’t think it’s the gas block, the worst that would happen on one that was not tuned properly is it would function like a bolt gun, pulling the charging handle to the rear would be effortless. On this rifle it gets stuck and needs to be forced open.
 
#4
With my sig762 ... when I closed the gas port (this was a piston gun) to permit it to be used like a bolt gun ... after firing, I could not pull open the bolt normally. It needed to be forced open with most ammo, but not with all.

Trying different parts and ammo is indicated. But if it runs fine with the port all the way open, I'd call that good also.

Oh and one more cause of the symptom I recall ... shooting a batch of steel lacquered WOOOOF ammo ... learned lesson ... no more steel lacquered ammo !!! :D

... I tried a different complete JP BCG, didn’t change anything ...
Click to expand...
Noted. And that's the next thing I would've tried.

What's wrong with leaving the port set to open ?? Given what you've said so far, I'd go with that.
 
#7
PrepareSmarter said:
Intentionally overgassing a gun to cover up the root cause of the issue will only increase recoil and potentially shorten equipment life.
Click to expand...

It doesn’t sound like it’s hammering anything, but instead it’s just starting to work. Might indicate that gas port is too small, gas block not positioned correctly, or other obstruction not allowing gas to get to the carrier, etc.
 
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#8
16" barrel with a rifle gas, any of the other 6 or 7 AR style rifles have rifle gas on a 16" barrel?
Distinct possibility that wide open on gas block is because of port size and limited dwell time.
Running suppressed?
What is port size?
 
#9
The only other 16” rifle length gas system I have is on a 5.56 gun. I am not sure of the size of the gas port, I have not put a suppressor on it yet.

The only reason I don’t think it has to do with to gas is because the bolt gets stuck, I have to grab the charging handle and slam the buttstock on a pic nic table to free it. When the gas is wide open it is enough force to send the bolt to the rear
 
#10
Bolt gets stuck because when the gas block is closed down the case doesn't extract and most probably the neck of case never clears chamber so case gets crammed back into chamber and viola, you now have to mortar the rifle to free it.
Gas block wide open, will bolt lock back on empty magazine, lock back on bolt stop (bolt stop catches between bolt and BCG) or bolt goes into battery?

M118LR, depending on what year you have, is pretty mild load. Might not have enough port pressure with the minimal dwell time to cycle this configuration.

What does a fired case mic at 0.200" above case head and just below shoulder?
What does a loaded round, virgin brass case mic at same points?
Any damage, excessive marring of fired case?

Sounds to me like the port is probably on small side for the minimal dwell time that a rifle gas on a 16" barrel offers but would probably be perfect for running a suppressor.

16" with rifle gas, IMHO, tends to be a bit more finicky and high strung to get dialed in. 16 with intermediate, 18 with rifle and 20 with +2 seems to work really well with out being a drama Queen.
 
#12
Who built the gun?
If it was built by a reputable gunsmith take it back and tell them to fix it.
If it was built by you then take it to a reputable smith and pay him to fix it since you are asking these questions.
 
#13
The cartridge cases are not damaged at all and the ammo is on the older side, it just seemed odd to me that the bolt was getting stuck, I never had that issue before. Typically when the bolt never came back while adjusting the gas block I would just rack it back, watch the brass eject and continue the process. I just wanted to get opinions before I prematurely sheard a lug off a $150 bolt or jacked up the chamber on a $500 barrel.
 
#15
sharfshutz762 said:
Who built the gun?
If it was built by a reputable gunsmith take it back and tell them to fix it.
If it was built by you then take it to a reputable smith and pay him to fix it since you are asking these questions.
Click to expand...

I built the gun, I am perfectly capable of figuring out the problem. Just taking advantage of the interwebs and seeing if anyone else has ever had this issue and if so what the problem was or just overall opinions.
 
#16
I had this same problem on a 6mmAR. The gas tube was a custom length and never worked for me. I tried trouble shooting it for some time. I had to slam the buttstock onto the table to get the spent round to eject. I tried adjusting the gas block. Checked the gas block positioning. Changed gas blocks. Changed gas tubes. Changed BCG. Changed spring. CHanged buffer tube weight. I about tried everything and sadly to say I never found out the problem. I sold the barrel saying I had issues for cheap and bought a 6.5 Grendel. Shoots flawlessly. Wish I had an answer but long story short it might be a chamber spec issue if you are using bought ammo. The 6mmAR did not have ammo off the shelf so it was all reloaded. I contacted the barrel maker and they couldn’t find the issue either.

In the end I’m not saying you have to sell or get a new barrel. Just what I found was the easiest solution for me. Works like a gem now.
 
#17
xNF_9 said:
I had this same problem on a 6mmAR. The gas tube was a custom length and never worked for me. I tried trouble shooting it for some time. I had to slam the buttstock onto the table to get the spent round to eject. I tried adjusting the gas block. Checked the gas block positioning. Changed gas blocks. Changed gas tubes. Changed BCG. Changed spring. CHanged buffer tube weight. I about tried everything and sadly to say I never found out the problem. I sold the barrel saying I had issues for cheap and bought a 6.5 Grendel. Shoots flawlessly. Wish I had an answer but long story short it might be a chamber spec issue if you are using bought ammo. The 6mmAR did not have ammo off the shelf so it was all reloaded. I contacted the barrel maker and they couldn’t find the issue either.

In the end I’m not saying you have to sell or get a new barrel. Just what I found was the easiest solution for me. Works like a gem now.
Click to expand...

I have a couple things I am gonna try tomorrow, see if that pans out. If not I am gonna call the barrel maker up and see what he says.
 
#18
wyld3man said:
The cartridge cases are not damaged at all and the ammo is on the older side, it just seemed odd to me that the bolt was getting stuck, I never had that issue before. Typically when the bolt never came back while adjusting the gas block I would just rack it back, watch the brass eject and continue the process. I just wanted to get opinions before I prematurely sheard a lug off a $150 bolt or jacked up the chamber on a $500 barrel.
Click to expand...

Port is small, minimal dwell time.
Don’t over think this.

AR extracts under pressure causing brass to be at / slightly larger than chamber dimensions so when case gets shoved back into chamber it sticks. BTDT, is pretty common actually.

Measure fired brass vs virgin brass, that’ll tell you if chamber has problem.

Does bolt lock back on empty mag?
If yes, is bolt behind bolt stop or is bolt stop between bolt & BCG?

ANY pressure signs on brass or primer?
 
#20
FCS said:
Port is small, minimal dwell time.
Don’t over think this.

AR extracts under pressure causing brass to be at / slightly larger than chamber dimensions so when case gets shoved back into chamber it sticks. BTDT, is pretty common actually.

Measure fired brass vs virgin brass, that’ll tell you if chamber has problem.

Does bolt lock back on empty mag?
If yes, is bolt behind bolt stop or is bolt stop between bolt & BCG?

ANY pressure signs on brass or primer?
Click to expand...


When the gas block is completely open, the bolt does lock back, everything functions as it should. There is not anything abnormal about the brass.

I am pretty certain the problem is exactly what you are saying. The minimal case expansion and tight tolerance of that chamber is causing it to get stuck.

I will measure the brass once I get home and see what the difference is.

The only 2 things I am gonna check out before calling it good is trying my other lower on that upper. JP silent captured springs had issues with PWS BCG’s. I have a PWS buffer tube with JP BCG and silent captured spring. Just curious, gonna see what happens. Then just run the situation by the barrel manufacturer see what he says. Just want to cover all the bases because I never had this problem before and all those parts were not cheap and I am learning a few things.

Funny thing is I would never had noticed anything if I had a regular gas block.
 
#22
I had a similar issue with a JP BCG, when I disassembled I found a small piece of the polishing media logged in the bolt cavity that was causing it to hang. I would disassemble just to be sure.
 
#24
bfoosh006 said:
This...,
And how many rounds fired thorough it ?

I general, all the Large frame AR's I have all tended to need a longer break-in period, for 100% function.
Click to expand...

Not many, plan was to adjust the gas block then zero then feed her a hot supper?, never got passed the gas block, probably 15 rounds. I was thinking about the break in also.
 
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#26
I had a tight chamber on a rifle once. I tried everything. Then I decided to use some polishing compound on a chamber mop, attatched to a drill. Fixed all my ejection issues. This is just something else to think about trying ifyou've exhauseted all other options. Good luck.
 
#28
I looked at thier site and could not find anything on thier chambers.
Some manufacturers run them tight, so nato ammo might be an issue.
Personally cant see a nato round barrel not being chambered that way for an ar.

Have you ran some 308 yet?
Did you save any fired rounds to measure head space?

My sons 308 bolt gun has a tight chamber but eats nato fine.
I dont have my notes here for comparison, but I think go gauge difference is 0.0005
But a larger difference in no go if memory works.

Did they give a reason they no longer use jp bolts? Worth a call.
 
Last edited:
#30
That is comforting to know.
My son just got his bolt 308 back at the shop. Time for load development.

I got 500 PC of 223 decaped an in first tumbler was sweet never hit dirt stuff.
Another 500 tomorrow.

Keep us up on the results and good shooting to you.
 
#31
I measured the cartridge cases for both fired and unfired 118lR and a live .308 Fed Gold SMK. I don’t have 100% trust in the accuracy of my calipers, I use them for wood working. (have too many hobbies right now to get into reloading) I measured both the length and diameter at the head.

Live 118LR 1.9975 and .4595
Fired 1.9910 and .4610
.308 live 1.9955 and .4585

Gonna go try .308 out of it and call the manufacturer to see what they say.
 
#34
called them up and explained the issue. They said the port diameter on that barrel is small, had they known I was using an adjustable gas block they would have opened it up a little ( didn’t know they would do that) they also said to try .308 ammo through it and if I still have the same issue to send it back.
 
#36
Here is a pic of the rifle, and the barrel. Boxed it up and sent it back
7049301
 

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#37
Very nice setup!
I bet they make it right for you, may end up with a new bolt out of pocket.
The old bolt may be fine with another barrel but I would be fine as long as it ran properly.

I dont know how to tune a bolt, wish I did, have not had to but extream accuracy
may need to learn.

Another 500 rnds of 223 deprimed and in the tumbler today.
 
#38
Snuby642 said:
Very nice setup!
I bet they make it right for you, may end up with a new bolt out of pocket.
The old bolt may be fine with another barrel but I would be fine as long as it ran properly.

I dont know how to tune a bolt, wish I did, have not had to but extream accuracy
may need to learn.

Another 500 rnds of 223 deprimed and in the tumbler today.
Click to expand...

I am sure it will work good once I get it back, it’s part my fault though. I didn’t tell them exactly what I had.

Having to force an expended cartridge case out of the chamber just didn’t seem right.

I am gonna get into re loading one of these days, been thinking about selling my wood shop to free up some time. I fly fish and my fly tying bench has been collecting dust also. My guns and fly rods are dust free though?
 
#39
Fly fishing is fun and in some places the best way to go, in Texas it's a small pastime.
Tying flies, fun but tedious and slow when you get old.

Reloading, very satisfying when you beat shelf ammo for accuracy .
Money saving at times. I'm retired and have time to do it so load for my 2 sons wife and me.
Less tedious than fly tying only concentrated mental effort realy is throwing powder
And load development / testing. The rest is easy, got bit and love it.

All the help you need is on the hide for expertise and fundementals from manufacturer's
sites.

Working out about 20 cents a round for 223 55gr with good results,
just a little more adjustment before we chisle the load in stone. Lol
 
Last edited:
#40
I received the barrel back yesterday, that was a fast turnaround and good customer service. Gonna head to the range in the next day or so to test it out.
 
#41
wyld3man said:
I received the barrel back yesterday, that was a fast turnaround and good customer service. Gonna head to the range in the next day or so to test it out.
Click to expand...

I was out of town for a little bit but finally got back and was able to go to the range. The rifle is GTG now, headspace being too tight was the issue. X Caliber customer service is pretty damn good. When they received the barrel back (and the bolt, which I did not have them headspace it to from the beginning. Wanted to but I was out of town then also) they sent it back same day. They also drilled the gas port out a little larger since I am using a low mass carrier and adjustable gas block.
 
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#42
wyld3man said:
I was out of town for a little bit but finally got back and was able to go to the range. The rifle is GTG now, headspace being too tight was the issue. X Caliber customer service is pretty damn good. When they received the barrel back (and the bolt, which I did not have them headspace it to from the beginning. Wanted to but I was out of town then also) they sent it back same day. They also drilled the gas port out a little larger since I am using a low mass carrier and adjustable gas block.
Click to expand...
Glad you're GTG and had great customer service!
 
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