SPR short-stroking problems *RESOLVED*

[bcw1284]

<span style="text-decoration: line-through">So I have recently acquired a new upper, with these specs:
Noveske 18" SPR barrel
midlength gas system
VLTOR mur-1a upper
Young MFG. chromed BCG

I popped it on an existing lower (mil-speck LPK inside and a2 stock w/ rifle spring & buffer). Upon the first range trip, the AR short stroked and refused to pick up the next round. It did successfully eject the spent case about 90% of the time, occasionally it would not. Once or twice I got it to grab a second round, but then it was a no-go immediately after.

The lower had JP yellow springs in it, so I went home and took them out. Back to the range, and still short stroking. Luckily, I had brought my RRA rifle as well this time, so I snagged its complete BCG and swapped it into the noveske.

BINGO, runs like a champ. Not one more FTF or FTE. It even ate some cheap russian ammo I had brought just to waste on the function tests.

What might cause one carrier to do this over another? I have inspected the Young carrier, and it looks fine. No burrs, properly staked, gas rings appear to be ok, bolt looks fine, extractor looks fine, wtf else might be the issue here?

TIA for any help, i've never had this issue before so i'm not really sure how to go about dealing with it. </span>

RESOLVED, see last post

 

[jakhamr81]

Re: SPR short-stroking problems

Was it a used carrier, perhaps clogged. Maybe try running a pipe cleaner and some solvent through the carrier key.

 

[Powder_Burns]

Re: SPR short-stroking problems

Assuming its new, tight like a virgin, cam pin may be binding enough to mess with proper cycling. If this is the case, it needs to be broken in. You can either shoot it and lube it until it plays nice, or hand cycle it half a thousand times until it frees up. Don't forget the lube.

 

[bcw1284]

Re: SPR short-stroking problems

I disassembled and cleaned the carrier, lubed it up, and still doing it. The pin does not seem to be tight enough to bind, but i'll check again.

 

[LimaBravo]

Re: SPR short-stroking problems

Field strip and make sure the bolt tail is perfectly clean.If not use green pad to scour off gunk until it looks like polished surface.The build up can cause stoppages if not properly cleaned.

Check the carier key on the one you had trouble with and make sure there isn't any play in it and is properly staked.

 

[bcw1284]

Re: SPR short-stroking problems

Everything seems to be just fine with that, the key is tight and staked well, far nicer than the RRA I replaced it with. There is no carbon buildup, I've cleaned it totally.

I suppose that it is possible that the carrier is a different weight? Also, the Young carrier has a titanium pin, and the other does not. Would that make a difference here? I would expect that to cause fail-to-fires (which I have not had), but not sure if that could create a feed issue?

I will just try the Young MFG carrier in a different rifle I guess, and maybe they can just trade permanently if it works without issue in that rig.

BTW- I have used several different mags throughout the process, and used them again after I got it working, so it's not the mags. 100% has to be that BCG, as nothing else will reproduce the issue.

Any other thoughts on this?

 

[bcw1284]

Re: SPR short-stroking problems

This is the carrier in question:
http://www.rainierarms.com/?page=shop/detail&product_id=1011

 

[ST42]

Re: SPR short-stroking problems

I had the exact same problem withe YNM BCG. It drove me crazy. I finally discovered that the hole in the rear of the BCG, where the bolt tail seats, was just slightly out of spec. It was allowing too much gas to pass through and it was causing the short stroking. I sent the BCG back to Young's and they sent me a replacement. Now it runs like a sewing machine.
By the way, when I spoke with whoever it was a Youngs, they were very skeptical. But they agreed with my assessment after receiving the bad BCG.

 

[bcw1284]

Re: SPR short-stroking problems

Do you remember what the proper dimension should be? That is something I could check with the calipers, and something I would not have thought of otherwise. Thanks!

 

[ST42]

Re: SPR short-stroking problems

Well, no. It was the only thing that I could think of as an answer to the SS. So what I did was to take another YNM BCG, which was also new. Along with a couple of other BCG's that I had, that all functioned properly, down to my local jewelry store. They had one of those long stainless steel tapered rods for determining ring size. I just inserted that rod into all the BCG's and the one that I was having trouble with was larger than the rest. Not very scientific, but it was repeatable, and there was a very slight difference.

 

[USACS]

Re: SPR short-stroking problems

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: STS</div><div class="ubbcode-body">I had the exact same problem withe YNM BCG. It drove me crazy. I finally discovered that the hole in the rear of the BCG, where the bolt tail seats, was just slightly out of spec. It was allowing too much gas to pass through and it was causing the short stroking. I sent the BCG back to Young's and they sent me a replacement. Now it runs like a sewing machine.
By the way, when I spoke with whoever it was a Youngs, they were very skeptical. But they agreed with my assessment after receiving the bad BCG. </div></div>
^^ This is likely the problem. Anytime a DI AR is short stroking, it's the result of a gas leak (or you're running an H3 or H4 buffer with an extra power recoil spring on a long gas system... ). Since you narrowed it down to the bolt carrier, there are two possibilities to be considered. The first is having an out of spec rear opening that release too much gas and prevents a good seal with the gas rings. Since STS has had the same problem with the same part, I would suspect that you have the same diagnosis.

The second possibility is that the gas key opening is not properly sealing around the gas tube. Since it's a new setup, a worn gas tube is out of the question. If you can take a loose gas tube and insert it into the gas key opening and there's virtually no play, then you have a good seal there. If there's a lot of play, then you have a leaking issue due to a bad mechanical seal. This could be a result of the key being out of spec or damaged. You would visually see the damage, but not if it was out of spec.

If that's also not the issue, then the problem likely lies with the seal between the gas key and bolt carrier. If there is some gap in there due to poor tolerances, damage or incompatible parts, gas will leak out of that gap between the base of the key and top of the carrier. This is usually at least partially visible, though, if you use a flashlight.

If you can manually cycle the bolt without issue using the charging handle, that eliminates a lot of mechanical issues. If you have any issues with binding, that's a whole other story altogether.

Do your best to get another BCG from the manufacturer. If it happens again, demand a refund and get something else.

 

[bcw1284]

Re: SPR short-stroking problems

Great info, thanks.

I'm going to function test the young carrier in a different gun tomorrow and see if it works there, and if it won't go in any of them then I will have to call them up and see about replacement.

I don't think any of my local jewelers would let me do that test around here, lol.

I'm going to go back through the carrier again and I will see if I can determine if it is out of spec. I thought Young was supposed to be the crem de la crem? I suppose bad machine work can happen to anyone though.

 

[zx1963]

Re: SPR short-stroking problems

Anywhere you have a difference in components you can have a gas leak which leads to short stroking..........

 

[5RWill]

Re: SPR short-stroking problems

Going out on the limb if nothing else fixes your problems that the others have mentioned. What ammo are you shooting? Some ammo is too "soft" to be run in a 0.63 gas port, if your using a mil spec gas tube. I have the same problem with some ammo on my BCM 14.5 mid.

 

[bcw1284]

Re: SPR short-stroking problems

It's the carrier for sure. I tried it in two other rifles today, not functional in either.

I just got off the phone with someone at Young MFG. (guessing it was Daniel himself) who immediately guessed my problem was short stroking and knew immediately why. He was very helpful and walked me through the inspection of the gas key. In the front of the gas key. behind the cam pin, the corner was not sealed up right. He told me this happens alot with the chromed ones.

I disassembled it while on the phone with him, and confirmed that it was assembled wrong.
1) the surface under the key had no sealant where it should have.
2)The screws had red loctite, as they should... but were also staked, which they are not supposed to be.

Dude was not too amused that it has been assembled wrong, so whoever is putting them together for him is not listening to the instructions.

He told me how to fix it, and offered to send out a call tag if it still won't work after I reseal it. I'm going to do it tonight and try it tomorrow after the sealant is dry. If it's still a no-go, then I will be sending it back.

CS was great, I have no problems with the company, just disappointed that their assemblers can't pay attention and do shit like they are supposed to.

 

[bcw1284]

Re: SPR short-stroking problems

One more update. I tried the sealant fix as directed, it did not work. At this point i'm beginning to wonder if something is out of spec or if it's just really that big of a PITA to seal this.

I called Young again, they said send it back for same-day turn around, which I appreciate since this fiasco has meant one of my rifles is down at all times while trading carriers around.

I will update again once this comes back from young MFG., hopefully they can fix it up like it should be.

 

[bcw1284]

Re: SPR short-stroking problems

**RESOLVED**

I received the carrier back from Young MFG. today and I couldn't be more pleased.

Enclosed was a personal letter from the owner, Dan Young, detailing the problem- the carrier was bored oversize just like STS posted earlier in the thread. Young MFG. replaced the carrier portion of the BCG and returned it with my existing bolt (which i'm fine with). They also refunded my postage, which I didn't expect them to do.

I am very pleased with the CS I received and I just wanted to make it known here that they are good folks who stand behind their products.

 

[jakhamr81]

Re: SPR short-stroking problems

Always good to hear when a manufacture takes care of their products and their customers.