Beyond tight upper receiver extension

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mongoose87

mongoose87

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Feb 14, 2018
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Hey guys

I have a BCM upper receiver and I am trying to install a Ballistic Advantage barrel. I am well aware BCM receivers are known for being super tight. Knowing this I greased up the interior of the receiver and the outside of the barrel extension. The barrel wouldn't go into the receiver at all. So I stuck the barrel in my freezer. Let it get nice and frosty then heated up the receiver and was able to gently hammer (rubber hammer) the barrel about 1/4 of the way in. Approximately 839 bludgeons with my rubber hammer later and the barrel extension pin is about halfway into the little receiver notch. I am so close but I cannot get this barrel to move a single thousandth of an inch further. I'd hate to take it to a gunsmith but I am nearing the point where I do not know what else to do. I have tried the freeze the barrel and heat the receiver combination 3 or 4 times. Is there anything I am missing?

thanks in advance!
 
can't speak to the gun world, but in all other things, mount the reciever in a vice, get a pipe wrench and rotate it while pulling. May take two people. Lots of duct tape, and a rag will minimize but not prevent scuffing the barrel. Goes without saying that you need to give up on getting it in at this point. Alternatively, a piece of pipe the diameter of the barrel extension hammered from the inside of the receiver, or both at the same time may be in order. A tight fit between the two should amount to a few taps with a plastic hammer. This sound like something was made wrong.
 
I'll add if the pins already started in the hole, you may get the barrel on using the hot/cold, while applying the barrel nut. Im sure others will suggest it. Be aware, if you do, theres a very real possibility of stripping the threads on the upper.
 
You might need to get the barrel cooler than the freezer. Two options here, dry ice and methanol bath or liquid nitrogen. Dry ice and methanol is easy to come up with, liquid nitrogen not so easy. Some large animal veterinarians have some on hand if they deal with AI.
 
If your are talking about a AR, something is out of spec. There is no need to do a thermal fitting if parts are right. The barrel should slide into the upper receiver, then tightened. The barrel extension nut is torqued to the barrel at ~150 ft/lbs, then the location pin is installed, and port drilled.
 
I managed to get it. I had previously left my barrel in the freezer for one hour max but I left it in there today for 4 hours and then heated the upper receiver. Surprisingly it closed the remaining gap in about two good whacks. Now I can finally get on with my build!
 
mongoose87 said:
. . . but I left it in there today for 4 hours and then heated the upper receiver. Surprisingly it closed the remaining gap in about two good whacks.
Click to expand...
We'll wait here for your thread next year asking how to remove a thermally-set barrel from an AR upper. . .
 
Judging by your comment I’m sure you’re such an expert ;). I don’t see why I would want to remove the barrel but if I did then it would be less trouble to just buy a new upper and barrel.

Thank you to all those who did actually offer real advice.
 
I’ve fit literally hundreds of AR barrels in the last ~20yrs, with that much interference, I would have concerns of fracturing the thread tenon, as it’s now under considerable stress. I’ve heated uppers many times to get a slight interference fit, but never to the extent of needing to hammer the barrel into place more than very light taps while inserting while hot & cold.

Personally, when I get an upper THAT tight, I simply use the shank of my lapping tool to lap the thread tenon slightly.

It’s not terribly expensive to throw away a forged upper with the barrel, and I have glued several barrels into their respective uppers over the years, but it seems as if this is a dying practice.
 
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