Just finished installing a Colt SOCOM 14.5" barrel in an Aero upper.
It was the tightest fit I’ve ever experienced and it took a few good whacks with a mallet to get the barrel extension seated and the indexing pin into position.
Are there any potential problems - aside from ever trying to remove the thing - from a very tight fit?
Should be fine. BCM uppers are known to be very tight as well. Try heating with a hair dryer or heat gun next time so it goes in a little easier.
This is a good thing. People do all sorts of crazy things like dump locktite all over the outside of their barrel extension to get their upper to barrel extension fit to be tighter.
So where are the pictures and build write-up? :big_boss:
Who is going to write that he split an upper while installing a barrel? 
It’s coming - once the thing is all done.
Just finished out a BCM Stripped upper with a Bear Creek Arsenal 16" Midlength 5.56 Barrel. Had to grab two thin boards, set the muzzle down on one and lay the other across the back of the upper. Only took a couple good wacks and it seated without needing a heatgun.
On the other hand, I had a 7.62x39 Barrel, from the same manufacturer, slide into a separate BCM upper like it was putting on a perfectly sized glove. It needed wiggling to seat, and a small tap from the palm to get the indexing pin into the slot. I would prefer to mallet them. Shows good sizing and dimensions. with a little heat, it’ll pop back out later on.
TL;DR: A tight receiver to barrel extension is never a bad thing until even a heat gun doesn’t get it on easy.
ETA: And don’t worry ToR, write-up and pics are coming (the write up side has been done for a bit, just waiting to get those pics). I am slated to get he BCM PKMR Midlength tomorrow morning. Last piece I needed after getting the Toolcraft BCG yesterday.
https://www.m4carbine.net/showthread.php?82447-PLEASE-READ-THIS-FIRST-Custom-Build-AR-Forum
Just saying…
Sorry, but I am not understanding your point…
Oh!
Woops, I was using the New Posts feature (normally do when perusing) and missed where this was even posted. I assumed it was in AR General or Technical. It’s what I get for the assumption. 
Usually I am quick to point that out as well.
Tsk tsk, OP. I thought ToR was hazing for posting about it, but not actually posting it built out.
Thanks for the clarification. Boy do I feel silly now. :jester:
Which shows you still haven’t read the link ToR posted. Read it, please.
I read the terms-just focused on the “ask questions” clause and not the “completed”. Mea culpa.
Mods, please move this thread. If this is a recurring issue, maybe re-title the sub forum to “showcase” or something more blatant?
In order to get a fit a really tight upper to barrel extension, I have had to put my barrel in the freezer and the upper in the oven at 350 degrees before mating them. Slipped right in, and then was ultra tight once back to room temp.
As said, a tight fit is my preference. Always lap the face of the threaded extension on the receiver too. I wrap my barrel extension with a flexible ice pa k and when ready heat the receiver end with a heat gun. Nice tight and hopefully straight fit.
I use BCM uppers (and lowers) almost exclusively for just that reason, the extension journal is slightly undersized to provide just that very thing, a nice tight fit. A lot of people who build specifically for accuracy will use one of the loctite products ( don’t remember specific product number) to coat the barrel ext if there is any amount of looseness. I prefer to just have the tight fit built in.
I personally discovered that little trick, the heating this and cooling that, while building 10-22s. Custom 10-22 barrels are a tight fit as well.
There is a company called BAT I believe, that makes a 1.00 &0.99" barrel extensions so they have a firm “press in fit”. Im considering this myself for a 20" build Im doing.
I believe that would be either green Loctite #638 or the slower drying #620.
There is a particular blue loctite that Bill Alexander used for the AA builds. I believe it’s considered a bedding compound rather than adhesive.
Pretty sure it was mentioned here in the archives.
Discussed here @ about 4:30
Yessir…this is where I got my info…really like these videos.
I saw it done in a vid by Criterion Barrels and yes it was green and yes more of a bedding compound and not an adhesive but I don’t remember the numerical designator. Why do I want to say 642? Whatever it was, it could work for loose barrel fit.
The Aero uppers I used on my last two builds were also very tight when mating a BA and LaRue barrel. I had to use a hair dryer to get them to mate. I was happy b/c I was dreading the possibility of a loose fit.
I’ve used 0.001" thick hardened stainless shim stock wrapped around the barrel extension to produce a “press fit” tight extension to upper fit. The before and after was especially noticeable in the reduction of vertical stringing as the barrel heated up after extensive firing. Easy and inexpensive solution. And much cleaner than Loctite.
The shim stock is available on Amazon in different thicknesses.