ultra match .223/556 not cycling

3

3blackdogs

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Minuteman
Feb 6, 2012
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stuck in time
#1
I put together a 18" ultra match upper

I can't get the gun to lock back on a single round fired. It will also not feed if the mag is in.
Rifle length gas system.

Jp adjustable gas block .(switched it out for a non adjustable one. Same issue)

Rifle length buffer and spring ( switched out to carbine setup in rifle length tube still wont cycle)

I'm out of ideas to make it run.
What should the diameter of the gas hole be? could the be the issue?

700 +- rounds on BCG
 
#2
Going to assume you're talking about a build with a Rainier Arms Ultramatch barrel. Did you follow their instructions for mounting the gas block? It has been to long since I built mine and don't remember if the gas block is to be mounted against the shoulder or set back to allow for the thickness of a handguard cap. It could be that if you mounted the gas block against the shoulder that you are restricting the gas flow through the gas port.

According to the answer to a question on their site, the port size is 0.101".
 
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#3
B y r o n said:
Going to assume you're talking about a build with a Rainier Arms Ultramatch barrel. Did you follow their instructions for mounting the gas block? It has been to long since I built mine and don't remember if the gas block is to be mounted against the shoulder or set back to allow for the thickness of a handguard cap. It could be that if you mounted the gas block against the shoulder that you are restricting the gas flow through the gas port.

According to the answer to a question on their site, the port size is 0.101".
Click to expand...
i put it together a couple of years ago. Life happen now im getting back to it. Ill have to go look in the box to dee if it had directions. Ill measure the Port to see where it all is.

Shoots great just wont cycle.. spot on at 100
 
#7
Hello. Sorry you are having issue. I would bet this is a gas block position issue. Many people install gas block all the way forward, so its touching shoulder/ledge of barrel. But each gas block and barrel have different position. Some are touching and some are 50 thousands off the shoulder. I would bet, its something like this. Push the gas block back so there is around a 30k gap from shoulder, then shoot that, do not use adjustable to test, use a standard, wide open one. You can also chamfer the port in the gas block slightly to allow for more install error.

Use standard 3 oz buffer and standard spring, not the rifle setup.

You can rule out that the gas tube is installed wrong, if you see the bolt move BACK when you fire.

Good luck with it. I think this will fix it. This is VERY common issue.
 
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#8
So you're saying the gun won't cycle. It will strip a round out of the magazine, fire, and eject but won't load the next round? It will shoot a single round, eject, but not lock back? If that is the case, then it is the gas system. One of the things not mentioned is to make sure the bolt key ois staked properly and not loose. This site is broken, so I can't post a picture, but it the part of the bolt that the gas tube mates with. As mentioned above make sure that the gas block is lined up with the gas hole in the barrel and the gas tube is lined up in the gas block. You can check this by plugging the muzzle and blowing air through the barrel.
 
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#10
yeah guys I took it all apart and reassembled it all. Then I plugged the barrel and blew down the end. I kept opening the gas block till it had good flow. Ill fire it in the morning and see what happens.
Thanks for all the help.
 
#11
3blackdogs said:
yeah guys I took it all apart and reassembled it all. Then I plugged the barrel and blew down the end. I kept opening the gas block till it had good flow. Ill fire it in the morning and see what happens.
Thanks for all the help.
Click to expand...

Instead of just randomly opening your gas block, read the instructions and set it to full open that way there is no guess-work as to it being fully open or not.
 
#15
If your barrel is conservatively ported, the adjustable gas block likely made things worse. All adjustable gas blocks leak.

Start with a fixed gas block and take some measurements to make sure that you are lining up the hole in the gas block with the hole in the barrel.

Did you try a different bolt carrier group?
 
#16
TonyAngel said:
If your barrel is conservatively ported, the adjustable gas block likely made things worse. All adjustable gas blocks leak.

Start with a fixed gas block and take some measurements to make sure that you are lining up the hole in the gas block with the hole in the barrel.

Did you try a different bolt carrier group?
Click to expand...
yes I put another BCG in it. I ended up putting teflon on the adj gas block screw. It was really a lose fit. way worse than my other Adj block. That seems to have done the trick. Fired a few more round and it feeds and locks open when empty. Not sure if Jp just had a bad threading on the block. I tried a few different set screws they all fit sloppy. I should try my non adj gas block on it now that I made the port a bit bigger. It was .079 made it ..099 need to get another gas tube to see if it fits a bit tighter into the block. that seems to have a good air leak at that connection also.
 
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