View Full Version : Barrel shank to Receiver fit
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gunnerblue
11-22-17, 20:32
With or without barrel nut installed?
I think with a quality barrel nut and proper assembly you'll be fine. Try it and see. An old-timer trick was to fill it up with 242 before torquing but I wouldn't recommend that.
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A lot depends on the purpose of the build. If not for a precision build, then check for play with barrel nut tightened lightly. If no play then when the nut is properly torqued, you should be OK from a functional point of view.
If its a precision build with a barrel that is expected to be very accurate based on reputation, then I would do as you said, and go with a tighter fitting upper receiver.
Another option if you want to salvage this upper is to use a sleeving compound from Loctite, not the common thread lockers, to eliminate the space between barrel extension and upper receiver.
Mark
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Nope, the receiver's not scrap. Once the barrel nut is properly tightened, it'll work fine for your intended purpose.
I'm sure it'll work....but I wouldn't be happy about it. The wiggle certainly will not help accuracy.
I've always had perfect fit with Noveske uppers - no wiggle, but not so tight that it's a struggle getting the barrel on. BCM upper are VERY tight...they recommend you heat the receiver prior to installing the barrel to allow easier installation.
BTW.. BCM has blem uppers marked down 40% for black friday.
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BTW.. BCM has blem uppers marked down 40% for black friday.
I just got mine in the mail yesterday. The only issue with it is the that the forge mark looks like a little blob. Otherwise it looks great. It is still engraved BCM4 on the face of the receiver so no forge mark isn't as big of a deal.
I'm on their site now, thinking it must be a sign that they have the blems in stock when I think I need one.
I am just gun shy about using the receiver when I know it's loose going into the build.
Andy
But you don’t “need” one. There will be no negative consequences for using what you have. But if you’re dying to get rid of it....I’ll destroy it for ya ;)
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There's no harm in trying what you have; assemble, shoot, evaluate. That's the only way to know for sure with any gun.
With a hand-tight ALG barrel nut, there is no movement.
It's not a precision build, I guess - I will have a MRO or a low power variable scope mounted.
Probably a non-issue (considering the platform and the application/intended use). However, if you are worried about it, you could do the following upon assembly:
1. Coat exterior of extension and interior of receiver with Rocksett.
2. Install barrel into upper receiver.
3. Torque down barrel nut, using a good moly grease on the threads (Aero Shell 64, etc.) and torque/loosen a few times before final torque.
4. Wipe off excess Rocksett from inside of receiver.
5. Cure with heat gun.
Aren't there shims you can put around the barrel extension that the High Power people use?
Aren't there shims you can put around the barrel extension that the High Power people use?
Sure, that's also an option. It's just a bit more of a PITA. If you have easy access to a good set of calipers (capable of both O.D. and I.D. measurements) and various shim stock, then by all means...
You would just want to have a piece wide enough and long enough to cover the entire extension, with only a small gap. I'd orient the gap to the 3 or 9 o'clock position, and cut out a recess for the extension pin to prevent it from spinning while assembling. YMMV...
Wouldn’t it be easier to simply shell out $100 for a new receiver?
Wouldn’t it be easier to simply shell out $100 for a new receiver?
Buying a new receiver and trying this one with the next barrel would be a legit option.
If it's loose again, then it's more worthy of being considered scrap.
Wouldn’t it be easier to simply shell out $100 for a new receiver?
Why? The barrel being loose doesn’t hurt anything if it tight when torqued, which he says it is. It would be a waste of $100.
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Why? The barrel being loose doesn’t hurt anything if it tight when torqued, which he says it is. It would be a waste of $100.
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I understand that it’s not an issue. However, it seems the OP sees it as an issue.
If it were mine, I’d torque it stand shoot the piss out of it
I have a NOS M4 upper made by a company that is long gone. There is detectable "wiggle" with the 2 barrels I tried in it. My instinct is that it's an interesting paperweight, and I should pick up a blem BCM upper to build on. Am I correct?y
I really, really like those BCM blem uppers and have used a bunch. For those unaware: https://www.bravocompanyusa.com/BCM-Upper-Receiver-Assembly-M4-Flat-Top-demo-p/flat%20top%20-upper%20-m4%20demo.htm
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