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Posted: 10/26/2013 5:49:11 PM EST
Anyone use the barrel shim kit to index the barrel nut for the gas tube listed on Gunbroker & eBay?
Link Posted: 10/26/2013 6:20:44 PM EST
Originally Posted By silentwind:
Anyone use the barrel shim kit to index the barrel nut for the gas tube listed on Gunbroker & eBay?
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Should never be necessary.
Link Posted: 10/26/2013 10:24:07 PM EST
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Originally Posted By Circuits:

Should never be necessary.
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Originally Posted By Circuits:
Originally Posted By silentwind:
Anyone use the barrel shim kit to index the barrel nut for the gas tube listed on Gunbroker & eBay?

Should never be necessary.



wow, yeah.

Link Posted: 10/27/2013 1:18:25 AM EST
Some barrel nut types require them. Factory shouldn't need one though but the majority of the aftermarket type would benefit. Mine came from spikes tactical.
Link Posted: 10/27/2013 3:22:57 AM EST
Why would any aftermarket barrel nut need one? You torque three times to 30 ft. lbs., then torque to the next index point.
Link Posted: 10/27/2013 3:24:37 AM EST
The last 300 Blackout build I did used a Seekins Bar rail. It required a shim kit. The kit has three different size shims that give you the ability to get the gas tube hole to line up correctly. It was very easy to use.
Link Posted: 10/27/2013 3:30:06 AM EST
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Originally Posted By Bhart89:
The last 300 Blackout build I did used a Seekins Bar rail. It required a shim kit. The kit has three different size shims that give you the ability to get the gas tube hole to line up correctly. It was very easy to use.
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I guess I just have to see the actual rail to understand the need for a shim.
Link Posted: 10/27/2013 4:24:22 AM EST
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Originally Posted By eracer:

I guess I just have to see the actual rail to understand the need for a shim.
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Originally Posted By eracer:
Originally Posted By Bhart89:
The last 300 Blackout build I did used a Seekins Bar rail. It required a shim kit. The kit has three different size shims that give you the ability to get the gas tube hole to line up correctly. It was very easy to use.

I guess I just have to see the actual rail to understand the need for a shim.

Link Posted: 10/27/2013 5:25:12 AM EST
I've built over two dozen ARs using at least 6 brands of forends and have never had to shim. Recall the barrel nut range is 30 TO 80 ft-lbs, not just going to 30. I tighten until I reach at least 30, then go to the next hole but never exceeding 80. If I am not where I want to be I back off and try again. It may take three tries, it may take 6 tries, but it always comes together eventally without shims or exceeding 80 ft-lbs. and I have never had a problem with any of my builds.
Link Posted: 10/27/2013 5:52:18 AM EST
I have one 11.5" barrel that I do need a shim for.
It ends up over torqued when I line up the next groove in the GI barrel nut.
Under torqued if I leave it under the first.

While it may not make sense, I've tried it with different barrel nuts and different upper receivers. No clue.

Dave N
Link Posted: 10/27/2013 6:29:03 AM EST
Keep tightening up to 80 then Break it loose again and retighten. Keep doing that and it will line up eventually. Been there, done that too many times.
Link Posted: 10/27/2013 7:00:23 AM EST
Using index marks and shims is just another way of doing the same thing. Some of those nuts are aluminum. It probably isn't a good idea to put a steel nut max torque spec on an aluminum nut.

You try that max torque and try again thing on a Seekins nut and it isn't going to get you anywhere, except for maybe elongated tool holes which means an out of round nut so you can't install the rail, a split nut, stripped threads, or a cracked receiver. Without at least some shim, the nut bottoms on the receiver.

Shims are used for some aftermarket systems. If someone is selling shims for standard barrel nuts, they are idiots. That is why you have a torque range for standard barrel nuts. If a standard steel barrel nut is bottoming out on the receiver, something is out of spec, and should be exchanged instead of shimmed.
Link Posted: 10/27/2013 7:58:02 AM EST
As long as the nut has enough torque on it and is lined up right, why does the method the person used to get there matter at all?
Link Posted: 10/27/2013 8:14:11 AM EST
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Originally Posted By Engel12626:
As long as the nut has enough torque on it and is lined up right, why does the method the person used to get there matter at all?
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No. I've done over a dozen ARs and never had a single issue. Tighten to the gas tube hole, past 30lbs and call it good.
Link Posted: 10/27/2013 8:36:57 AM EST
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Originally Posted By Engel12626:
As long as the nut has enough torque on it and is lined up right, why does the method the person used to get there matter at all?
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It matters because different systems are made of different materials. What is good for one may not be good for another.
Link Posted: 10/27/2013 2:44:58 PM EST
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Originally Posted By Bhart89:
Originally Posted By eracer:
Originally Posted By Bhart89:
The last 300 Blackout build I did used a Seekins Bar rail. It required a shim kit. The kit has three different size shims that give you the ability to get the gas tube hole to line up correctly. It was very easy to use.

I guess I just have to see the actual rail to understand the need for a shim.

http://i42.photobucket.com/albums/e314/bhart8911/5d208ad8d9ea17d1e61714fa58c514e4_zps79eb8a19.jpg


OK, I understand now. Weird design.
Link Posted: 10/28/2013 1:40:03 AM EST
99% of the time, no shim needed to properly torqued & align the barrel nut. The 1% of the time that I ran into didn't want to align no matter what I did. Solved it by re-timed the upper with a fine flat file (don't attempt this method unless you know what you're doing.)
Link Posted: 10/28/2013 4:57:57 AM EST
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Originally Posted By bravo5two:
99% of the time, no shim needed to properly torqued & align the barrel nut. The 1% of the time that I ran into didn't want to align no matter what I did. Solved it by re-timed the upper with a fine flat file (don't attempt this method unless you know what you're doing.)
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The correct method of facing a receiver:

Brownells
Link Posted: 10/28/2013 5:41:24 AM EST
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Originally Posted By PursuitSS:


The correct method of facing a receiver:

Brownells
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Originally Posted By PursuitSS:
Originally Posted By bravo5two:
99% of the time, no shim needed to properly torqued & align the barrel nut. The 1% of the time that I ran into didn't want to align no matter what I did. Solved it by re-timed the upper with a fine flat file (don't attempt this method unless you know what you're doing.)


The correct method of facing a receiver:

Brownells


This is similar to how I do it. I use a perfectly flat marble plate and 320, 600 and 1000 grit automotive sandpaper to remove material off the front of the barrel extension. Most upper recievers I have used have been a little long. If you look where the feed ramps in the upper meet the feed ramps on the barrel, you will end up with about a 1/64" + or - to work with. I'll get my feed ramps as close to flush as I can where the barrel nut will line up perfectly with the gas tube at 50ftlbs. Making sure not to go past flush is important.
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