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[ARCHIVED THREAD] - Barrel extension loose in upper receiver?

Posted: 1/20/2018 7:43:17 PM EDT

Question... building my 3rd AR which has an Aero Precision upper and Faxon heavy fluted barrel. On my previous two builds, the barrels (both Ballistic Advantage) were a nicely tight but not too tight fit to the upper (both Aero), but this one fits right in so easily there is a small bit of play. I use aeroshell grease when mounting but this one will still probably not be tight. Will this be an issue once torqued down? Any accuracy issues? The goal of this one is to be a precision AR, so any input is appreciated.

Posted: 1/20/2018 9:04:20 PM EDT

[#1]

Bed it with Loctite.

Posted: 1/21/2018 8:03:01 AM EDT

[#2]

Some Teflon tape too

Posted: 1/21/2018 4:02:44 PM EDT

[#3]

^^^ I lol'd.

Conventional wisdom is that for a precision build, you don't want slop there. Instead, fit it with shims and loctite. You'll want to do some googling.

Posted: 1/21/2018 4:05:10 PM EDT

[#4]

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Some Teflon tape too

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Just don't. ^^^

Posted: 1/21/2018 4:39:23 PM EDT

[#5]

Quote History

Quoted:
^^^ I lol'd.

Conventional wisdom is that for a precision build, you don't want slop there. Instead, fit it with shims and loctite. You'll want to do some googling.

View Quote

Googling commenced, and I've learned some things today. Will have to figure out which size and where to get the shim stock, but at least there's a plan. Thanks!

Posted: 1/21/2018 5:06:08 PM EDT

[#6]

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Quoted:
Googling commenced, and I've learned some things today. Will have to figure out which size and where to get the shim stock, but at least there's a plan. Thanks!

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Quoted:

Quoted:
^^^ I lol'd.

Conventional wisdom is that for a precision build, you don't want slop there. Instead, fit it with shims and loctite. You'll want to do some googling.

Googling commenced, and I've learned some things today. Will have to figure out which size and where to get the shim stock, but at least there's a plan. Thanks!

It's debatable whether or not this play between upper and barrel extension really leads to any noteable loss of accuracy. I would do what the large majority here do and bed it with loctite. It's an acceptable method that's simple and works well.

Posted: 1/21/2018 6:54:34 PM EDT

[#7]

indian head gasket shellac compound.

Posted: 1/21/2018 7:07:08 PM EDT

[#8]

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Quoted:
indian head gasket shellac compound.

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This can be used, but it makes a huge mess. Also makes future disassembly, clean up, and reuse of parts damn near impossible. Loctite is a MUCH better alternative.

Posted: 1/21/2018 8:45:22 PM EDT

[#9]

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Quoted:

It's debatable whether or not this play between upper and barrel extension really leads to any noteable loss of accuracy. I would do what the large majority here do and bed it with loctite. It's an acceptable method that's simple and works well.

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Dunno about "loss", but certainly not to the barrel's capability. Joe says there's improvement of "about 1/3 the original group". So 0.7 MOA to 0.5 MOA, 0.5 to 0.35, etc.

Building Match Grade AR-15s

https://www.youtube.com/watch?v=pJL-IscH_jo

Posted: 1/21/2018 9:23:37 PM EDT

[#10]

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Quoted:
Dunno about "loss", but certainly not to the barrel's capability. Joe says there's improvement of "about 1/3 the original group". So 0.7 MOA to 0.5 MOA, 0.5 to 0.35, etc.

https://www.youtube.com/watch?v=pJL-IscH_jo

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Quoted:

Quoted:

It's debatable whether or not this play between upper and barrel extension really leads to any noteable loss of accuracy. I would do what the large majority here do and bed it with loctite. It's an acceptable method that's simple and works well.

Dunno about "loss", but certainly not to the barrel's capability. Joe says there's improvement of "about 1/3 the original group". So 0.7 MOA to 0.5 MOA, 0.5 to 0.35, etc.

https://www.youtube.com/watch?v=pJL-IscH_jo

@HighpowerRifleBrony

Yeah, I've seen that.

I've tested this myself with an upper I had that wasn't shooting to what I believed was it's full potential. It started life installed in an upper without being bedded. The barrel extension fit the upper decently tight, but there was a bit of play. I then removed the barrel and bedded with loctite during the reinstallation process. I know it was loctite and not shim stock, but loctite is an acceptable method. It shot the same as it did before, with no noticeable changes in accuracy, better or worse.

That said, I understand it's only a sample of one and some may have had the opposite experience.

Posted: 1/21/2018 11:17:36 PM EDT

[#11]

Hm, what barrel was that?

Posted: 1/22/2018 12:17:54 AM EDT

[#12]

I'd like to see some real data. As in, shoot some groups with a loose barrel/receiver combo, take it apart, apply loctite, shoot groups again, compare results. I can understand why theoretically it could make a difference, but if it truly does, it ought to be measurable.

Posted: 1/22/2018 12:32:22 AM EDT

[#13]

When you have a loosely fitting barrel extension, you first have to figure out if its the barrel or the receiver. Use a micrometer to check the barrel and a snap gauge and micrometer to check the receiver. Call the manufacturers of both items to get the specs. Odds are you get an answer like, it's Mil Spec from the receiver folks. The barrel folks should be better at getting you the numbers. Whichever one is out of spec, get it replaced. O.K. that's all sounding really good but in reality, please don't bed your barrel nut, it does no good whatsoever. Well maybe it does some good but it's not needed. All you really need to do is lap the receiver so that the front edge is flat and then use a reaction bar to center the barrel while you torque the barrel nut. Get some barrel nut shims, you may need them to get the nut aligned properly after you lap the receiver.

Posted: 1/22/2018 2:32:35 PM EDT

[#14]

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Quoted:
Hm, what barrel was that?

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@HighpowerRifleBrony

16" Noveske Recon. It shot decent groups, but admittedly I was expecting better. Thought pulling the barrel and bedding it would help, but unfortunately, I saw no difference.

I should've tried lapping the receiver face, but I didn't. If I still owned that particular upper I would. Would have made for an interesting test.

Posted: 2/8/2018 4:47:54 PM EDT

[#15]

Bedding the barrel ext into the upper may or may not help, but it should eliminate a potential variable which seems desirable when building for accuracy.

Posted: 2/9/2018 6:50:19 AM EDT

[#16]

Quote History

Quoted:
When you have a loosely fitting barrel extension, you first have to figure out if its the barrel or the receiver. Use a micrometer to check the barrel and a snap gauge and micrometer to check the receiver. Call the manufacturers of both items to get the specs. Odds are you get an answer like, it's Mil Spec from the receiver folks. The barrel folks should be better at getting you the numbers. Whichever one is out of spec, get it replaced. O.K. that's all sounding really good but in reality, please don't bed your barrel nut, it does no good whatsoever. Well maybe it does some good but it's not needed. All you really need to do is lap the receiver so that the front edge is flat and then use a reaction bar to center the barrel while you torque the barrel nut. Get some barrel nut shims, you may need them to get the nut aligned properly after you lap the receiver.

View Quote

At least someone got it half right. Novel idea to promote the idea of measuring parts to see if your parts are spec. Ideally, you want to do this before you buy them unless you're purchasing from a known good source. Another lost idea is don't be a cheap ass. Just buy quality parts from go and this woodshed gunsmiff BS becomes unnecessary. "Bedding" the barrel with Loctite or any other type of epoxy or goop in a tube is just retarded. So is lapping your receiver. Neither do anything except enrich the Brownell brothers.

Posted: 2/9/2018 7:43:33 AM EDT

[#17]

Uppers are done when the barrel is done.

If you are like most AR owners you get your upper and never break it down. If you decide you want another cartridge you get a new upper, either home build or factory. If you home build and find it loose you have the choice of another $$$ purchase of a single use tool or a $5 purchase of a pack of JB Weld. Both work, lapping and epoxy, only one is the wise way to do it for a guy at home building one upper every couple of years.

I used JB Weld and it worked great. If I every build another upper from scratch and I find it a bit loose I will do it again.

Posted: 2/9/2018 4:16:33 PM EDT

[#18]

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I used JB Weld and it worked great. If I every build another upper from scratch and I find it a bit loose I will do it again.

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I got married and had children, but am still not capable of THAT level of commitment.

Posted: 2/9/2018 8:48:05 PM EDT

[#19]

Quote History

Quoted:

At least someone got it half right. Novel idea to promote the idea of measuring parts to see if your parts are spec. Ideally, you want to do this before you buy them unless you're purchasing from a known good source. Another lost idea is don't be a cheap ass. Just buy quality parts from go and this woodshed gunsmiff BS becomes unnecessary. "Bedding" the barrel with Loctite or any other type of epoxy or goop in a tube is just retarded. So is lapping your receiver. Neither do anything except enrich the Brownell brothers.

View Quote

Just to add, I tried measuring the extension and upper, but my calipers aren't consistent or accurate enough evidently. As for quality parts, it's an Aero Precision upper and Faxon heavy fluted match barrel. I think most would say they are decent quality parts, no? I think it's just that some combinations will fit perfectly and some won't, no biggie. When it's time to assemble I'm going to try the shims, which sounds like a good and easy fix. Appreciate the replies.

Posted: 2/9/2018 10:45:02 PM EDT

[#20]

Quote History

Quoted:

Just to add, I tried measuring the extension and upper, but my calipers aren't consistent or accurate enough evidently. As for quality parts, it's an Aero Precision upper and Faxon heavy fluted match barrel. I think most would say they are decent quality parts, no? I think it's just that some combinations will fit perfectly and some won't, no biggie. When it's time to assemble I'm going to try the shims, which sounds like a good and easy fix. Appreciate the replies.

View Quote

I use Aero Precision uppers regularly. Faxon probably doesn't make their own barrel extensions. I'd trust the Aero upper before the Faxon barrel extension.

Posted: 2/9/2018 11:51:08 PM EDT

[#21]

Spec off the print for the upper for inside diameter of the nose is 1.000 +.002/-.000
Barrel extension .9987 -.0008 with final dimension after surface plating not to exceed .9999

Posted: 2/10/2018 8:00:33 AM EDT

[#22]

Quote History

Quoted:
Spec off the print for the upper for inside diameter of the nose is 1.000 +.002/-.000
Barrel extension .9987 -.0008 with final dimension after surface plating not to exceed .9999

View Quote

The Aero upper measured 1.0005 and the barrel extension (unknown manufacturer) measured .9995. The problem is market specs are all over the map. + diameter raceways and - diameter extensions reduce returns.

I'd love to find a source for broached / single point cut barrel extensions. I don't think they exist but I'll keep looking...

[ARCHIVED THREAD] - Barrel extension loose in upper receiver?

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