A2 does not cycle

[esaabye]

I have an bushy A2 20inch Hbar and it is no longer cycling correctly. Today it ran fine for 30 rounds then slowly turned into a bolt action rifle. The bolt would catch 3/4 back then not at all. Same load I normally shoot and that shot fine from a 16inch today so I think it is the rifle.

Where do I start looking for the problem?

I cleaned it tonight, dripped some clp down the gas tube and it drained fine.

[Help][Help][Help]

[GunTroll]

I have an bushy A2 20inch Hbar and it is no longer cycling correctly. Today it ran fine for 30 rounds then slowly turned into a bolt action rifle. The bolt would catch 3/4 back then not at all. Same load I normally shoot and that shot fine from a 16inch today so I think it is the rifle.

Where do I start looking for the problem?

I cleaned it tonight, dripped some clp down the gas tube and it drained fine.

[Help][Help][Help]

You and me both guy!

[esaabye]

You and me both guy!


You inspired me.

Just a strange thing, worked fine for 1st several thousand rounds but now, bolt action.

Think I must have plugged up the gas port or the tube but not wanting to take it apart yet.

[Backinblackrifles]

I have never seen a clogged tube or port to much pressure. I don't advise sticking anything down it either You probably wont get it back. Check for binding of the carier and gas tube by stripping the bolt carier and runing it up and down by hand listen and feel for any binding. I would bet this is the problem aspecialy if it works well the first mag or so it is fouling and binding. Clean the gas/carier key out realy well soak it over night in brake cleaner then scrape out the carbon fouling wich is usually hard as a rock from being baked in. Also no ball powder or laquered cases.

[spencerhenry]

bushy with bushy mags? i have seen several bushmasters that with factory supplied mags are unreliable. try some other mags, that fixed the problem with the ones i am familiar with.

[Hoser]

Gas issue.

Check your front sight for leaks.

Maybe it needs some oil..

[esaabye]

Gas issue.

Check your front sight for leaks.

Maybe it needs some oil..


So I torn it down after talking with the guys at Bowers and reading the suggestions on here. Could not find a problem, gas tube is clean, gas rings are good and hold, everything lines up.

I was putting it back together when I rememberd that I had modified the charging handle by sealing the gas port so I would not get blowback. I am hoping this was the cause of the poblem, by not allowing the release of the spent gas out the rear it could act like a compression break and slow the bolt.

We shall see Saturday.

[Quib]

I recently did a write-up on AR15 troubleshooting, with a list of probable causes.

Maybe it can get you headed in the right direction....

http://http://www.weaponevolution.com/forum/showthread.php?2442-Principles-Of-Troubleshooting-And-The-AR15 (http://www.weaponevolution.com/forum/showthread.php?2442-Principles-Of-Troubleshooting-And-The-AR15)

[BPTactical]

I think we are overlooking something very simple here.
Sounds like possibly a gas key has started to loosen. Clean your bolt carrier/key well with some BrakeCleen or similar and allow it to dry. Take one drop of solvent and carefully place said drop in the gas key and allow it to run into the bolt carrier. Examine the joint of the gas key/bolt carrier carefully. If you see ANY evidence (wet) of leaking at the joint then you must have the key lapped and reinstalled.
You can check your gas block the same way.
With the bolt sticking @3/4 it sounds as if it is short-stroking.

One other thing to check-Make sure that the hole on the upper stock screw is not plugged/blocked in any way. If it is you will get a short-stroke because of the retardation of the buffer traveling. All it takes is slowing it down by milliseconds to throw the entire timing cycle off...

If you are still stumped shoot me a PM.
Good info Quib.......

[Quib]

Good info Quib.......

Thanks. It's a constant work in progress.

If anyone has something to add to the list, please let me know. I'm in the process right now, of converting the text into TS Charts.

[esaabye]

Thanks. It's a constant work in progress.

If anyone has something to add to the list, please let me know. I'm in the process right now, of converting the text into TS Charts.

Thanks everyone, I got out today and spent some time swapping parts between 2 rifles to pinpoint the issue.

The problem follows the bolt carrier but not the bolt so it must be the gas key. I tested it as suggested and can see no sign of a leak but must have an issue none the less.


So now for the next step, I look for a smithy to fix it. How much should I expect to pay to have the key removed and restaked?

[henpecked]

Thanks everyone, I got out today and spent some time swapping parts between 2 rifles to pinpoint the issue.

The problem follows the bolt carrier but not the bolt so it must be the gas key. I tested it as suggested and can see no sign of a leak but must have an issue none the less.


So now for the next step, I look for a smithy to fix it. How much should I expect to pay to have the key removed and restaked?


Can you blow thru it? If not you got a primer lodged in there.

[BPTactical]

Can you blow thru it? If not you got a primer lodged in there.

If the gas key was plugged you would notice the increase in recoil and it will eject really hard. The relationship of the bolt/carrier slows down the gas impulse a bit by bleeding some of it off through the vent holes in the BC.
Short stroking is a sure sign of gas leakage.

[Quib]

Thanks everyone, I got out today and spent some time swapping parts between 2 rifles to pinpoint the issue.

The problem follows the bolt carrier but not the bolt so it must be the gas key. I tested it as suggested and can see no sign of a leak but must have an issue none the less.


So now for the next step, I look for a smithy to fix it. How much should I expect to pay to have the key removed and restaked?


So, keeping the original Bolt and swapping Carriers corrected the problem?

I'd take a look next at the gas path through the Gas Key, check for blockage. If the Gas Key gas path is plugged, that could be your problem. Depending on the cause/type of the blockage, you could correct this yourself without the help of a smith.

Some other possibilities:


Interior of the Gas Key worn? Causing gas loss between the Gas Tube and interior of the Gas Key? How is the condition of the portion of the Gas Tube that enters the Gas Key? Worn smooth?



Interior of the Carrier worn? Causing gas loss between the Bolt Rings and interior of the Carrier? Performed the Bolt Ring Wear Check?



ETA: I cover both those topics here: http://www.weaponevolution.com/forum/showthread.php?1613-FAQ-s-BASIC-INSPECTIONS-AND-PROCEDURES

[Quib]

If the gas key was plugged you would notice the increase in recoil and it will eject really hard.

Correct me if I'm wrong, but a blocked Gas Key gas path would render the weapon inoperable. The weapon would not cycle or eject at all.

[Quib]

Can you blow thru it? If not you got a primer lodged in there.


It's a possibility.......http://www.weaponevolution.com/forum/showthread.php?1989-Gas-Key-Obstruction

[henpecked]

Correct me if I'm wrong, but a blocked Gas Key gas path would render the weapon inoperable. The weapon would not cycle or eject at all.


Mine would not cycle or eject. Primer was lodged in gas key.
Unable to blow thru. Took a nail and hammer, one smack and I was back in business.

http://www.weaponevolution.com/forum...ey-Obstruction

Picture shows exactly where mine was lodged

Only had it happen once since 1977

[BPTactical]

Correct me if I'm wrong, but a blocked Gas Key gas path would render the weapon inoperable. The weapon would not cycle or eject at all.

Generally true- but I have worked on two rifles that had lack of gas flow issues that resulted in very sharp and erratic cycling. One rifle was a late manufacture Bushy that had the gas port drilled off center on the bolt carrier and the other was a gunshow special of unknown pedigree that had a FUBAR gas key. Both rifles cycled erratically and recoiled very harsh(for an AR) and launched brass into the Stratosphere and really dinged it badly. I replaced the BC on the Bushy and the gas key on the mutt and both cycled fine afterwards.

All an AR needs is rearward motion imposed on the bolt carrier to unlock the bolt and overcome the buffer spring. On a gas impinged AR this is done by the gas impulse. On a piston AR this is done by the op rod shoving on the boss where the gas key used to be. I think on the 2 rifles aforementioned the gas impulse was enough to cycle them but seeing how none of the impulse was bled off through the vents on the bolt carrier that resulted in the hard recoil and launching the brass quite far for an AR. The brass was also severely damaged on both.

[Quib]

Generally true- but I have worked on two rifles that had lack of gas flow issues that resulted in very sharp and erratic cycling. One rifle was a late manufacture Bushy that had the gas port drilled off center on the bolt carrier and the other was a gunshow special of unknown pedigree that had a FUBAR gas key. Both rifles cycled erratically and recoiled very harsh(for an AR) and launched brass into the Stratosphere and really dinged it badly. I replaced the BC on the Bushy and the gas key on the mutt and both cycled fine afterwards.

All an AR needs is rearward motion imposed on the bolt carrier to unlock the bolt and overcome the buffer spring. On a gas impinged AR this is done by the gas impulse. On a piston AR this is done by the op rod shoving on the boss where the gas key used to be. I think on the 2 rifles aforementioned the gas impulse was enough to cycle them but seeing how none of the impulse was bled off through the vents on the bolt carrier that resulted in the hard recoil and launching the brass quite far for an AR. The brass was also severely damaged on both.


Interesting. Thanks for the update! :)

[esaabye]

OK, just did some more digging and testing.

So at this time I have isolated the issue to the BC with gas key installed. Everything else works fine but problem follows BC with key.

Looking at blocked key I did the suggested blow air test and it seemed fine, compaired to working BC with key it felt the same.

I ran a pipe cleaner thru the key and it passed without problem. used a pick and it felt the same as the working one.

I then put the bolt back in the locked position and filled the key with oil with the BC set on end. A slight amount of oil showed at the front of the key but very little and when testing the known good it did the same.


[Bang][Bang][Bang][Bang]

Visually both carriers look the same, no odd wear marks to suggest a contact point.

I am now better informed on the troubleshooting side but not feeling any closer to a solution. Will visit with a smithy Tuesday but don't want to spend more then a replacement would cost.

Time for a beer.

[BPTactical]

Any oil is too much as far as leakage, given the viscosity of oil imagine how much gas is leaking @ 40,000 psi!

Check your PMs

[ERNO]

I had a failure to fully cycle rearward in my AR-15,16 inch barrel;when I installed a hydraulic buffer in my stock.I reinstalled original buffer: problem solved.

[theGinsue]

Lots of great information in these pages. I've got an early model Colt SP1 having a lot of these same issues. I've been too lazy to take this thing apart to the degree I need to TS, too lazy to actually begin, and too embarassed to ask.

Now I've got lots of great info to check out and perhaps get the problem with the SP1 solved.

[esaabye]

Lots of great information in these pages. I've got an early model Colt SP1 having a lot of these same issues. I've been too lazy to take this thing apart to the degree I need to TS, too lazy to actually begin, and too embarassed to ask.

Nopw I've got lots of great info to check out and perhaps get the problem with the SP1 solved.


Looks like I may have found the problem. The smith at bowers pointed out the the carrier I had was (I thing) a SP1 type with reduced area on the bottom. I recently replaced the trigger with a RR 2 stage and the combo is the problem (he thinks but it all fits). I ordered a new M16 carrier with key from Bravo for $65, will know for sure next week.

pic below is colt carrier like mine.

http://biggerhammer.net/ar15/barrelsbolts/sp1_boltassembly_later_bottom_moremetalmachinedawa y.jpg

[Quib]

In your OP, you stated the weapon ran fine for about 30 rds, then stopped cycling.

If the issue was a parts compatibility one between the un-shrouded bolt carrier and FCG, I would think the weapon would exhibit these signs from the beginning, and not over a period of time.

[BPTactical]

In your OP, you stated the weapon ran fine for about 30 rds, then stopped cycling.

If the issue was a parts compatibility one between the un-shrouded bolt carrier and FCG, I would think the weapon would exhibit these signs from the beginning, and not over a period of time.

This +1
What was described in the original post was a degenerating condition, as the weapon was fired the condition worsened.
Something changed the more the weapon was fired i.e. gas leak.
The shroud length of the BC is not the problem. If the bolt carrier can travel far enough back to cycle the weapon then the hammer is getting cocked unless the RR trigger group has been monkeyed with.
If the weapon cocked and stayed cocked after the RR trigger group was installed then the BC is not likely the problem. This would be discovered by a basic function check after the weapon was reassembled.

FWIW- I have swapped bolt carriers between all of mine and all cock and lock with either the shrouded and unshrouded bolt carriers.

Interesting-keep us posted.

[esaabye]

In your OP, you stated the weapon ran fine for about 30 rds, then stopped cycling.

If the issue was a parts compatibility one between the un-shrouded bolt carrier and FCG, I would think the weapon would exhibit these signs from the beginning, and not over a period of time.

I do not disagree, but the gas key looks fine and the only difference is the carrier design. I had not noticed the difference until the guy at bowers pointed it out.

I forgot about the change in trigger.

[Quib]

Well, obviously the Carrier swap narrowed down the issue. But, I do not believe the issue is the Carrier being the un-shrouded type.

As BP stated, please keep us posted! :)


ETA: Did you check the items I outlined on the last page?

Some other possibilities:

- Interior of the Gas Key worn? Causing gas loss between the Gas Tube and interior of the Gas Key? How is the condition of the portion of the Gas Tube that enters the Gas Key? Worn smooth?

- Interior of the Carrier worn? Causing gas loss between the Bolt Rings and interior of the Carrier? Performed the Bolt Ring Wear Check?

[henpecked]

Any updates on this?

[esaabye]

Yes, good news is Bowers' smith (can't remember his name) was right. The issue is the combo of the reduced bolt carrier and the Rock River trigger. For whatever reason the trigger geometry is such that it slows or retards the bolt carrier just a bit and it fails to cycle.

I moved the BC to serveral other rifles and it works fine, just not with the one I shoot. All othyers work fine in my A2, just not the reduced BC and only after trigger upgrade to RR.

I purchased a M16 carrier from Bravo to replace it and moving on. Happy now.

Thanks for all the good info, will come back to this thread in the future for reference.