gas piston problems.

[Meat-Hook]

I have a Bushmaster gas piston upper that has suddenly decided to start malfunctioning. I got this a couple of years ago and still has less than 500 rounds thru it. It suddenly started closing on an empty chamber. Pull the trigger an "CLICK"!,..empty chamber. sometimes it does it with rounds in the magazine and sometimes it does it after the last round has been fired. Today it also halfway fed a round into the chamber and stopped. It resumed firing again and got about 30 rounds off then it went back to malfunctioning.

when this all started I thought it was the magazine. Tried several magazines of different makes. Made no difference. Switched out the gas piston upper and put on a standard Bushmaster 20" gas impingement upper. Inserted the same magazines firing the same PMC ammunition and the ate everything it was fed with no problems as it always has. Switch back to piston upper and its malfunction city.

anybody know what is causing this?? and how to fix it???

[Vulcan]

Check your front end for gas leaks and make sure the space (should be none) between the push rod and the carrier face that it interacts with is correct. Something could have gotten loose in there some place.

[paintballmagnet]

Short stroking due to leaks, worn, broken or loose parts as Vulcan stated. The last couple years since piston AR's have become the "thing" its seems I hear of more reliability issues with piston AR's than I ever ran into with gas tube models. My perception only?

[ISC]

It's time for someone to come up with another solution to fix a problem that doesn't exist for the M16 design. I nominate an "improved" magazine release.

[Old Man of the Mountain]

Originally Posted by paintballmagnet

Short stroking due to leaks, worn, broken or loose parts as Vulcan stated. The last couple years since piston AR's have become the "thing" its seems I hear of more reliability issues with piston AR's than I ever ran into with gas tube models. My perception only?

I agree, short stroking could explain that.

If the gas system is adjustable (some are) then open it up some and feed it more gas.

It could be the ammo, PMC might be on the low pressure side a bit, a different brand might have more gas pressure for the piston (it might take more gas to drive the piston system than just gas impingement by itself).

[Hooch]

ISC...THAT was funny!

[mgjohn]

It also need an improved bayonet lug and bayonet.

[Vulcan]

I am using a TNW kit and it leaks like crazy. 10.3" barrel and runs like a rapd ape. The space between the rod and bolt face opened up and sheared a bolt in the key. I replaced the modified M16 carrier with the full gas piston carrier. No problems to date. Just something you need to keep an eye on. The piston is a great idea but I think it needs to be a purpose built system rather than the modified systems. The ones that reaplce the entire gas system are best (front site base on back).

[Meat-Hook]

Update:

just got thru cleaning this thing after returning from the range. I think I *might* have figured out the problem---then again, mabe not.

I have a dedicated upper, not the retrofit kit. According to the Bushmaster owner manuel, it says that when re-assembling, to re-insert the gas piston with the 2 rings in first,..facing the butt stock. If you look under the "Disassembly of gas piston components" section
http://www.bushmaster.com/faqs/attac...anSuppl-GP.pdf

HOWEVER,.....

On Bushmasters "Frequently Asked Questions section it says the opposite. It says to re-insert the gas piston with the 2 rings facing the muzzle.
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http://www.bushmaster.com/faqs/afmvi...spx?faqid=1859

Question / Issue

I have a new bushmaster with the gas piston. At first I had no problem( the first 100 rounds) then I tried to shoot some wolf ammo and the problem started.It would eject the spent round but would not feed the next round from the clip and i would have to manually chamber the next round.So i went back to the rounds that feed with no problem and it woked fine (no problem).I took the gun home and cleaned it .went back to the range and the problem started with the good ammo.One shot ejected fine but didn't feed next round..a couple of times the next round would start to feed and get jamed, tried different mags ,still won't feed next round. I picked up my brass and noticed that the round neck on my spent rounds had a small dent on the top of them.(The very top of the neck of the spent cartrige had a small dent that made a useally round circle into a circle with a small flat spot on every spent round).I don't no what is going on but I have to manually chamber every round now.I kept shooting chambering each round, but every once in a great whiile it would chamber the next round by itself. I used different mags (factory bushmaster 30 round mags) same problem with all three mags.Please Help!! Thankls,Charles

Answer / Solution

It is normal for the fired brass to have a dent in it from the brass deflector. Sometimes they are on the mouth of the case like yours or in the side depending on the ejection path.
I need to know if you have the dedicated gas piston carbine or a unit with a gas piston conversion.
If it is a dedicated upper the piston may be reversed causing the short stroking. The instruction sheet shows it installed in reverse of the way it should be. It should be installed with the two grooves facing the muzzle for normal operation. It is reversed with the single groove forward with the smaller holes for use with a sound suppressor which creates back pressure.
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So I turned turned the gas piston so the rings were facing the flash hider. Fired 4 boxes of PMC, 3 boxes of winchester white box, 3 boxes of american eagle red box. It ate all of them without a hitch Except for when I used the C-products 10 round mag. After it closed on an empty chamber and I heard that "click", I set aside that magazine and did not use it again with the gas piston upper. I changed out uppers to the 20" gas impingement upper and re-inserted the C Products mag. The 20" upper ate all the ammo fed by the C-Products mag.

Im still not convinced Im out of the woods yet. Ill have to send another couple hundred rounds thru it ((minus the C-products mag)) to be convinced thats what the problem is/was.

thanks for your replies.

stay tuned,...the saga continues.

[Meat-Hook]

another update.

took it to the range today. 5 boxes of PMC/100 rounds. Kept firing and firing without a hitch. I fire the last round ((# 100)) and CLICK!!.....it closes on an empty chamber. I load a few rounds and it fires and then closes on an empty chamber and keeps doing this.

Back to square 1.

I dont no what to do with this thing. I dont know whats causing it to do this nor what the solution is.

Is it doing this when the barrel gets hot and the chamber gets dirty???? or what? I guess Ill be forced into calling bushmaster. Im reluctant to do so as my experience with gun factories in the past is that they are gun assemblers and know nothing of trouble shooting nor gunsmithing.

for an upper that alone cost $1,100 this pisses me off.

[MrBlack]

Hook, my advice to you is to sell that thing and recover what you can from it. AR15 series guns are designed to be gas guns, not piston guns. All these things we see today are just aftermarket add ons. Piston guns are designed and purpose built like that. Today, there are a couple uppers that are purpose built, not add on parts like the majority of them are. I know this is not what you want to hear but just in my pro-fesh-nil opinion and years of cleaning and examining gas piston, both long and short stroke, tappet systems and comparing the designs to impingement systems, I think you have either one or the other. Piston systems are not used on rotary bolts, in general, and the rare instances they are, the bolts typically have no more than 3 lugs and are rotating while engaging into battery, not rotating then unlocking or locking into battery. Closely look at the locking lugs and action of an M1 carbine, a short stroke tappet design or of a BAR, a long piston design. The action of a piston is immediate and violent, the action of gas impingement is immediate but much softer in operation if that makes any sense The add on systems are a hybrid of both and just flat prone to ghostly problems, there is just too much happening in the cycle of an AR bolt and barrel extension during locking/unlocking for a piston to be as effective. All of this is just based on my experience and knowledge of both systems operational characteristics and, of course, a fair amount of opinion and general disgust with hippies........
Good luck...
Mr. Black

[partisan50]

I have a lot more rounds out of both of my LWRC uppers, with and with out the supressor and I have had no problems with either unit.

[Meat-Hook]

Update:

I sent the upper back to Bushmaster. They worked on it and had it back to me in 2 weeks. The invoice said they had installed parts and test fired 120 rounds thru it---no charge to me.

I disassembled the upper to see what they did. It appeared that they had installed a whole new gas system. I opened the gas cylinder and tilted the barrel forward. Nothing came out. I thought; where the hell is the gas piston? I looked in the gas cylinder and there it was. It was in there so tight, that I had to go inside the receiver and push on the gas tube rod in order to inch the gas piston out of the cylinder. Once the nose of the gas piston was out, I had to grab a hold of it with some pliers in order to get it out. Thats how tight it was in there!!

With the old gas cylinder, it was in there so loose,..you just tilted the barrel forward, once you opened the gas cylinder, and the piston just plopped out.

So I didnt know what to think. If its in there so tight this thing might blow up when I fire it. Today was the first chance I had to take it to the range. I fired the first few rounds and I noticed the difference right away. The recoil was so much more robust that it felt like the rifle was vibrating with so much more power with every shot fired.

Fired 140 rounds of PMC. ZERO malfunctions.

So,.....with the old gas system, it must have been leaking tons of gas.

When it came time to close up shop for the day, I went to fold down my front BUIS and almost burnt my fingers. I forgot that all the heat and gas is now vented down the barrel close to the front sight. Man, that thing gets hot in a hurry. I also saw smoke coming thru the handgaurds at times-----I think I got a little generous with the oil before taking it to the range.

all in all, Im a happy camper tonight. The problem appears to be fixed. I know Im not out of the woods yet as I want to send a few more hundred rounds thru it before Im totally convinced.

I give Bushmaster customer service 5 stars. They listened to my situation without any argument or resistance. They fixed the problem in minimal time and sent it back. Both on this situation and the broken butt plate situation. Both times their customer service has been swift and excellent. All these problems can be forgiven/forgotten just so long as a company has good customer service.