Posted: 8/27/2016 9:07:13 PM EDT
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I've had this upper for a couple of years now, 16" mid-length light weight hammer forged, BCM BCA.. Love it. It came with a Gunfighter mod 0 compensator. The rest of the rifle is an Anderson lower with a PSA parts kit, standard carbine buffer and spring and all Magpul MOE furniture. The thing always ran like a scalded dog. Lately I have gotten bit by the suppressor bug. I ordered a YHM Titanium .30 ULT. While waiting on Uncle Sam to do his thing, I started gathering the quick connect mounts for it to go on various rifles.
Last night, the Gunfighter Mod 0 came off and a YHM quick connect Phantom Flash hider went on in its place. Took it shooting today and it is now short stroking. Tried various ammo and magazines all with the same results. If you put a death grip on it and don't let it move, it will run through the whole mag without fail. As soon as you give it a little wiggle room, it fails to eject and/or feed. I'm pretty sure the Gunfighter Mod0s construction causes it to create back pressure, which allowed the rifle to run properly. Once it was removed and the YHM Phantom, whos construction being very open doesn't have a hope of creating any back pressure, it now seems to be under gassed. Is there anything short of having the gas port opened up going to fix it? I'm sure putting the suppressor on when it comes will make it run, but I really don't want to HAVE to have it on to run. Thanks for any help! 
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standard carbine buffer and spring I would think buffer if it ran before. The standard buffer has different weights. I would check and maybe try a lighter one. Other than that, I do not know. Difference Between AR-15 Buffers |
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Quoted:
I would think buffer if it ran before. The standard buffer has different weights. I would check and maybe try a lighter one. Other than that, I do not know. Difference Between AR-15 Buffers Quoted:
standard carbine buffer and spring I would think buffer if it ran before. The standard buffer has different weights. I would check and maybe try a lighter one. Other than that, I do not know. Difference Between AR-15 Buffers Thanks for the info. I just weighed my buffer. 2.965oz. Where do I get a lighter than standard carbine buffer? |
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'Short Stroking" seems like a buffer. I have the same upper and I just looked. I have the H buffer. The only thing I can think of is the bolt is outrunning the dwell time of the rifle cycle with the new compensator. In other words it is running too fast and needs to be slowed. It is highly unlikely you developed a gas leak just changing the flash hider.
My lower is a Stag Arms lower and I do not think your lower could be your problem EDIT- I am still thinking you are running too fast for your mid-length gas system. I would also consider an extra power buffer spring, but I usually do not like to go that way. Carbine H Buffer search |
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'Short Stroking" seems like a buffer. I have the same upper and I just looked. I have the H buffer. The only thing I can think of is the bolt is outrunning the dwell time of the rifle cycle with the new compensator. In other words it is running too fast and needs to be slowed. It is highly unlikely you developed a gas leak just changing the flash hider. My lower is a Stag Arms lower and I do not think your lower could be your problem EDIT- I am still thinking you are running too fast for your mid-length gas system. I would also consider an extra power buffer spring, but I usually do not like to go that way. Carbine H Buffer search Don't think the buffer is the problem. Weighed it, just short of 3oz, so standard carbine buffer. The only change made from running well, to short stroking was the change from a muzzle brake to a flash hider. The Gunfighter Mod0 construction seems to produce considerable back pressure. The YHM Phantom suppressor mount flash hider is completely open and produces none at all. The bolt carrier isn't out running the dwell time, it is not running fast enough to be reliable under normal conditions. If I anchor it down hard on a bag and not let it move at all, it cycles fine. Problems come when you assume a normal shooting hold, whether off hand or on the bench. I don't really want to mess around with lighter than normal buffers and what not. Looks like I'll have to have the gas port opened up. |
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Can't see how a heavier buffer is not going to make a short stroking rifle worse.
If I hold it in a death grip, it cycles perfectly. If you hold it in a normal way, it doesn't, it fails to eject. It is short stroking, not cycling too fast. Only change was the muzzle device. It went from being 100% with the Mod 0 muzzle break 
to 50% with the YHM Phantom suppressor mount 
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Sorry, I did not explain what I was talking about very clearly. I found this to troubleshoot your rifle
Short Stroking |
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Sorry, I did not explain what I was talking about very clearly. I found this to troubleshoot your rifle Short Stroking Thanks for the link. That info just seems to me to confirm under gassed condition. It ran like a sewing machine with a muzzle break whos design obviously creates back pressure. Putting on a flash hider that does not create this back pressure with no other changes, same magazines, multiple NHMTG 30rd with Magpul followers, same ammo, IMI m193 and PMC X-Tac M855. If you gorilla grip it and don't let it move as it cycles, it runs perfect. Over gassed and doing this would only exacerbate the problem. The minute you let it move at all, it fails to eject. It needs a little more ass in the carrier speed. 
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put the BCM back on and confirm function again just to be 100% something else didn't come loose or whatnot. That's the plan, once I get some free time to head back out to the boonies. This isn't my only BCM upper and I wasn't expecting any problems or I would have taken the break and the wrench with me. Hind sight as they say. |
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Update. Finally went to the range again. Put the original muzzle break back on. Still short strokes. Swapped uppers to a known good lower. Still short strokes. Swapped bolt carrier to a know good bolt carrier. BINGO. Rifle runs like a sewing machine again. BCM bolt carrier swapped in to rifle bolt carrier came out of, short stroke.
So, it has developed a problem with the carrier. Haven't had a chance to look it over yet. At the range I couldn't find any obvious problems with it, but it was dirty, and I didn't have any allen keys to check if the key screws were loose, but the key didn't move with hard finger pressure. Will update when I get a chance to look it over better. Update: Broken key bolt. Rear one is tight, front one spins, will not tighten, staking won't let it come out either. Will contact BCM. Email sent through "Contact us page of BCM website. BCM responded-Return arranged-Will go out today. |
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Well glad you have a possible fix. I was going to guess the gas block was moved slightly during muzzle device removal. I know...not a great guess but that would definitely downsize the gas port. It has a pinned front sight, and I'm not King Kong, so I didn't even think about that.
It's just weird the way it happened. I was literally shooting the rifle the day before I changed the muzzle break out and it was running great. Put on the YHM suppressor mount flash hider and took it out a couple of days after and it immediately started short stroking, which is why I guessed it was under gassed at first, since the YHM mount is open as hell, no chance it's creating any back pressure at all, unlike the BCM device. Once I changed the bolt carrier out to one from another rifle we were shooting at the same time, it went right back to sewing machine. The screw had to snap during the last rounds fired just before I changed out the break. 
Shit happens. Key screws snapping isn't one you hear about a lot, but I have heard about it happening. All is good.
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Quoted:
It has a pinned front sight, and I'm not King Kong, so I didn't even think about that.
It's just weird the way it happened. I was literally shooting the rifle the day before I changed the muzzle break out and it was running great. Put on the YHM suppressor mount flash hider and took it out a couple of days after and it immediately started short stroking, which is why I guessed it was under gassed at first, since the YHM mount is open as hell, no chance it's creating any back pressure at all, unlike the BCM device. Once I changed the bolt carrier out to one from another rifle we were shooting at the same time, it went right back to sewing machine. The screw had to snap during the last rounds fired just before I changed out the break.
Shit happens. Key screws snapping isn't one you hear about a lot, but I have heard about it happening. All is good. Quoted:
Quoted:
Well glad you have a possible fix. I was going to guess the gas block was moved slightly during muzzle device removal. I know...not a great guess but that would definitely downsize the gas port. It has a pinned front sight, and I'm not King Kong, so I didn't even think about that.
It's just weird the way it happened. I was literally shooting the rifle the day before I changed the muzzle break out and it was running great. Put on the YHM suppressor mount flash hider and took it out a couple of days after and it immediately started short stroking, which is why I guessed it was under gassed at first, since the YHM mount is open as hell, no chance it's creating any back pressure at all, unlike the BCM device. Once I changed the bolt carrier out to one from another rifle we were shooting at the same time, it went right back to sewing machine. The screw had to snap during the last rounds fired just before I changed out the break.
Shit happens. Key screws snapping isn't one you hear about a lot, but I have heard about it happening. All is good. LOL!!! Well in that case it probably wasn't the gas block then.
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