Originally Posted by
Ned Christiansen
556cliff, I was diggin' everything you said until your showed the pic. Bottom row, third from left, scrap that abomination!:eek:
Here's my take. First, when we install a barrel, the barrel itself is not really a participant. We are installing a barrel extension. I illustrate this in classes when we do the barrel change segment, by demo-ing a barrel installation and then hand-unscrewing the barrel from the barrel extension. I have it set up before hand obviously that the barrel is only in hand-tight, but it illustrates that the barrel itself wasn't really involved. I demo a variety of tools for doing this job-- the clamshell, the Reaction Rod, the MagPul Bev Block, and the Midwest Industries Upper Receiver Rod. The latter in my opinion is the only one that can really do the job right. Without the barrel extension and upper receiver being held positively in alignment and completely immobilized, we would be transmitting torque to something we shouldn't, especially that tiny little locating pin. I like a setup where only the nut can turn, the MIURR accomplishes that, at least as best it can given that there has to be a certain amount of clearance between its top locating rib and the cut in the receiver that it fits into, and likewise between its front splines and the barrel extension. The Bev Block does the same thing in theory but I feel like doing it up through the magwell is not as positive. The Bev Block is a very clever design and using the carrier itself as a rear stabilizer was smart but I just think the URR does it more precisely.
My setup prior to the URR was to clamp the upper in my mill vise since on an M4 upper we have two parallel surfaces and the mill vise closes flat, straight and parallel-- then I clamped the barrel to an angle plate that was clamped to the mill table. In that setup the upper and barrel are immobilized but-- I was still trusting the threaded relationship bewtween the barrel and barrel extension to be ight enough to resist any movelemt=-- which generally, it is. But still not the most ideal setup. I like the URR better for home use and I have never used anything but these two setups except for the rare carry-handled upper, for that, prior to the URR, I used the clamshell.
I know guys who do more barrel work than I do by a factor of maybe 100 or more, and they use a variety of the above tools and others. One uses the block where the lugs for the takedown pins fit into the block and you pin the upper in through the takedown pin holes. This does not seem like a good setup to me.... but all these guys seem to get it done OK. There have been some instances of damaging the locating pin or its slot in the upper, and one pal advises he has torn the threaded neck out of a couple uppers when trying to inch over the high torque spec to get perfect gas tube line-up....! At the end of each demo just for comedy relief I try to do that by getting medieval on the torque and I never accomplished the break-off until recently, but that upper had been through the attempt maybe eight times. I guess this guy is a lot stronger than me or has a long pipe....!
But the original question was lube. I tell the class to use whatever grease is handy but get the recommended anti-seize if you can. Get some grease on the threads, both male and female, no need to get sloppy with it, and make sure there is a little on the front of the flange, that's a friction point too. No grease, but rather clean and dry, on the rear of the flange and front face of the receiver. That has to help it resist any turning force. In fact if I were making these darn things and of course this is in "cost is no object" fantasy land here, but the receiver's front face and barrel extension would have interlocking cuts all round so we weren't relying on that stupid 1/8" pin up against an aluminum slot.
The barrel extension OD where it fits into the upper, I epoxy that. Gotta do it neatly and tr4y to not let any get between the flange and the receiver face-- so it mostly goes in the upper. Some are pretty sloppy and I figure it can't hurt to fill that space with something. If it eventually turns to carbon crumbs, OK, as long as it's in there taking up space. I'd rather it was metal to metal and I have at times been able to slip some .001 or .002 shim stock in there. I think the thermal-fit is a great idea, maybe they should all have been that was going way back. Aluminum expands at ~twice the rate of steel so it's a perfect place to make use of that fact. Metal to metal is always better-- more solid, better heat transfer.
A few years ago I kinda polled some of the shops that service the NRA Hi-Power crowd, some used LocTite (red as I recall) to lock the barrel extension into the receiver (not on the threads). One told me don't sweat it, the receiver neck will collapse down onto the barrel extension as the nut is torqued up-- to a degree I'm sure it does but I don't think it would be true "full contact". I can't prove that gluing the barrel extension in helps but I feel safe in saying that a gap in there doesn't help.