AR buffer issue?

[length_of_pull_1]

I recently assembled a new upper with a 223 Wylde 20" barrel. It has a rifle length gas port. I put it on a lower with an adjustable carbine style stock. On my first trip to the range the bolt wouldn't hold open after the last round round in the magazine and I got several failure to feed malfunctions. I am assuming that the rifle length gas system isn't sending the bcg back far enough to engage the bolt hold open and is causing a short stroke failure to feed. This is my first rifle length build so I am a little inexperienced with the issues associated with them. My knee jerk reaction is to find a lighter buffer, but any input would greatly appreciated. Thanks in advance!

 

[readyeddy]

I had the same problem. I changed to a lighter spring and stopped shooting cheap ammo. Malfunctions stopped.

 

[12Bravo20]

It almost sounds like the upper is either under gassed or something in the gas system is out of line. What ammo were you shooting? Try some surplus M193 55 Gr or M855 62Gr ammo. I have seen where 223 ammo doesn't have enough power to completely cycle a brand new rifle until broken in. As far as the carbine stock and buffer, it should be fine with an upper with rifle length gas system. The military has used that setup quite a bit when they put adjustable stocks on M16 A2 and A4 rifles. Try some full power 5.56 ammo for break-in.

 

[Varminterror]

There’s no reason a rifle length gas system cannot work with a carbine stock and buffer - even using an H2 buffer as it should be, let alone the underweight Carbine buffers commonly used.

If it’s not locking back, the real issue is that it is under-gassed for the ammo being used. If you’re using low powered ammo, or less reputable ammo, then the fix is likely simple. If you are using standard power ammo, then it’s a problem with the gas system. It may be binding, poorly fit, dragging on the mag, or otherwise cycling poorly, but reducing buffer weight below H2 or reducing spring power to correct this issue is akin to taking aspirin for brain cancer. Reducing the reciprocating mass might alleviate some symptoms, but it’s not going to cure the real disease.

 

[length_of_pull_1]

Thanks for the info! I think I'll make sure the gas block is lined up exactly right (I thought I took care to make sure it was), and after that I'll try some different ammo. The lower is definitely broken in, it has been run with different uppers, all carbine length gas systems with adjustable gas gas blocks mostly to keep my brass from ejecting straight forward. I was using both Federal 55gr 223 fmj and some middle of the road 60gr hand loads, but I can certainly crank out some stronger loads and I have some 68gr pills that should add something to that equation. I guess I needed an excuse to get back to the range!

 

[12Bravo20]

Run some good 5.56 ammo through it. That will tell you right away if there is a problem with the gas system.

 

[HankC]

Likely small gas leak at gas block while new, keep shooting, after hundred rounds or so, carbon will seal it off and you will be fine.

 

[12Bravo20]

Right or wrong, this is what I do every time I build/assemble an upper with a 5.56 or 223 Wylde chamber.

1. After upper/rifle is assembled and lubed, I manually work the action at lest 100 times.
2. I shoot at least 100 rounds of M193 or M855 ammo before trying any other ammo.

I haven't had a problem no matter what gas length/buffer length combo I use by doing this. I have used rifle length uppers with carbine stocks and carbine length uppers with rifle stocks

HankC is also correct that you can have a slight gas leak that will seal itself.

 

[sarduy]

Check if you put a rifle length buffer spring in a carbine buffer tube. It can put a bit more pressure to the bcg

 

[Skylerbone]

New BCG or borrowed? Test your bolt to make sure rings are good, inspect carrier key.

 

[js8588]

Who makes the barrel?

 

[readyeddy]

Federal 55 grain shouldn't give you problems. I was getting short stroking from steel case MFS 223, but XM193 was no problem.

For some reason the stock buffer spring in my Bushmaster XM15 was stout. I replaced it with a standard spring from Brownells and then I was able to shoot the weaker steel cased ammo with no problem.

 

[length_of_pull_1]

Who makes the barrel?

It came from CBC Industries, 223 Wylde 20" 1in8 Nitride. I'm not sure who cut it.

 

[length_of_pull_1]

New BCG or borrowed? Test your bolt to make sure rings are good, inspect carrier key.

The BCG has been used some before but just gently. The rings are great and the gas key has the slightest wiggle to it but otherwise it's looks fine.

 

[Demi-human]

and the gas key has the slightest wiggle to it .

Ta Daa!

This is your problem. If it’s loose it can drag, and leak, and misalign.

It is not fine. Properly staked and tight is the way. Adjust the gas tube to it.

Or yes, better ammunition, check gas block, gas port.

 

[12Bravo20]

Ta Daa!

This is your problem. If it’s loose it can drag, and leak, and misalign.

It is not fine. Properly staked and tight is the way. Adjust the gas tube to it.

Or yes, better ammunition, check gas block, gas port.

All the above.

 

[Riomouse911]

Ya, the gas key shouldn't wiggle at all. I could see where it could even damage the end of the gas tube if it's slamming back home a bit off-line and striking the edge of the gas tube with the edge of the key.

Tighten it up, grab some good ammo and you'll be back in business in no time.

Stay safe.

 

[Skylerbone]

You’ll actually want a new key and hardware plus Permatex sealant per procedure. Be sure to have the appropriate punch to stake it on hand. Never try to re-use any of these parts, your face is worth it.

 

[cfullgraf]

The solution may have already been suggested.

But, as a something to think about, I built a couple 204 Ruger AR-15's with long barrels. They would not reliably hold the bolt open on the last round. Appearently, the bolt was moving too fast on recoil. The solution was I had to make the buffer heavier and slow the bolt carrier down a little so that it would catch the bolt catch.

Granted, this was with rifle length stocks, buffers, and gas systems.

 

[js8588]

It came from CBC Industries, 223 Wylde 20" 1in8 Nitride. I'm not sure who cut it.

Yeah, as said above, your problem is the gas key BUT if CBC Industries assembled the upper, I would also check the gas block alignment & barrel nut torque. If I didn't assemble the parts myself, I don't 100% trust it.

 

[length_of_pull_1]

Thanks guys! I did reposition the gas block because it was a little off (not sure it it was off enough to restrict the gas flow, but I made sure it was aligned dead nut, and I did notice some carbon streaks along the side of the tube coming out of the block, so there must be a very tiny leak there. I am going to reset the gas key with some permatex and the torque wrench that's on the way today. Range tomorrow. I have a good feeling it's going to work well!

 

[ms6852]

Hope this link helps with your problem, please read it.
https://www.at3tactical.com/blogs/n...-rifle-a-beginner-s-guide-to-ar15-gas-systems

 

[length_of_pull_1]

Success! Thanks again for the input! After resetting the gas key, the thing works like a dream. I think I've learned a thing or two working through this problem. I found that the gas key wasn't staked worth a damn. The dimples in the sides made it to where the screws couldn't back out of their hole, but they sure could turn underneath the staking. So apparently that tiny wiggle that was there was all gloom and doom. I used permatex, and torqued the screws and restaked the thing according to m16/m4 repair and maintenance manual I found. I only went about a hundred rounds, but everything worked flawlessly. I'll keep looking at it in the future but I am very happy with the staking job I did and am pretty sure that won't happen again. One more time... Thanks!

 

[Demi-human]

Glad everything worked out for you.

Proper stacking moves the key metal and the screw metal. It doesn’t let the screw turn at all.

Many good rounds to you and your rifle!

(I meant staking. Darn Auto-Assume.)