This is going to be a stupid question, but: How do I clamp my barrel in vise blocks when tightening the flash hider after installing a full-length rail?
Do I just use receiver blocks and not worry about stressing the barrel indexing pin/barrel nut area? 
I just hold the receiver area between my knees and tighten it up a bit. Iâm not so sure it needs to be tightened up as much as you may be planning to do.
What if Iâm going to be using the FH as a suppressor mount?
Thanks,
Jason
This is where Brownells wrench which holds the barrel extension is really nice. Ideally you should clamp the barrel itself into the vise. There are times that are less than ideal such as in this case. As long as you donât go over around 40 Ft lbs you should be fine just holding by the receiver. Be very careful, if you canât get it off then take the rail off or weaken the flash hider by cutting slits in it but not all the way through or you hit you muzzle threads. You can always try the freezer trick to.
Iâve changed several hundred flash bidets on SBRs where I had no access to the barrel and havenât caused any damage to any of them.
I use the DPMS claw mount, it works great solong as you have a decent vise.
Cool. Great tool, I use one too.
However it does nothing to protect the aluminum upper receiver from the steel indexing pin on the barrel extension as youâre twisting the barrel inside this receiver by cranking on the flash hider which also put pressure on the barrel indexing pin against the aluminum receiver.
Mil spec for FH torque is (I believe) 15-20 ft-lbs.
KAC spec for the Triple Tap is 20-30 ft-lbs
Looking at the length of barrel protruding on a 14.5" barrel with a DD RIS II, it looks like there might be enough to grab onto if I cut down a set of barrel blocks.
However, one of THESE might require the use of the Brownells tool.
What prevents the barrel from turning inside the barrel extension when using the Brownells tool? Donât they just thread together too, with no locating pin?
The barrel and the barrel ext. themselves. These are both RH threads and the indexing pin is drilled and pin installed after the bbl ext in torqued.
There is no torque value when installing a military type flash hider using a crush washer. You simply turn the flash hider until the center slot of the hider is in line with the center of the FSB.
You should be able to use an upper receiver vise block to do it. I have several times.
Originally Posted by eternal24k
I use the DPMS claw mount, it works great solong as you have a decent vise.http://www.dpmsinc.com/store/productâŚ=1675&cat=1450
Mount the upper to the dpms claw, then put it in the vice at 90 degree angle, so the vice is contacting the bottom of the claw and the top of the upper (use wood or something to protect the rails).
This is very solid and allows zero twisting of the upper, as apposed to relying on the pins. I had an extremely tight barrel nut I was about to give up on. This did the trick, nut came right off with no worry about the upper.
Actually this is such a solid method they should include instructions and an additional piece for the top of the upper specifically for this.
With regards to how tight you need to torque the FH, itâs not so much a matter of how tight is enough, itâs that you sometimes need a lot of force to get that last bit for a proper index.
I think youâve missed my point entirely.
Tightening the barrel nut does not hurt the upper receivers indexing pin notch. Tighenting/loosening the flash hider could because itâs in turn turning the barrel within the receiver. (The receiver is aluminum the barrel indexing pin is steelâŚwhich do you think will win?) As long as you donât go nuts on the torque of the flash hider youâll be good. Like I said earlier ideally you want to clamp the barrel into barrel blocks into the vise when cranking on flash hiders.
Guys, be careful on this. When I started working on ARs about 7-8 years ago, I ruined 2 new Colt upper receivers trying to get a couple of Surefire suppressor adaptors to line up correctly. During the trial and error of âadd a shim, remove a shim, add a different shim, etcâ my barrels started turning in the upper receivers and the barrel index pin damaged the alignment notch pretty severely on both. I ended up scraping both uppers because of the damage. Since the barrel extension and barrel nuts generally have a liberal coating of anti-size on them anyway, there is not a lot keeping the barrel from turning when you start cranking on the muzzle device.
I talked to Ken Elmore as well as some very high grade military armorers and the consensus was to always clamp the barrel or front sight tower when working with muzzle devices. Especially when fitting muzzle devices that line up via a series of shims, which often require full torque on and off several times, the barrel can start shifting left/right and damage the upper. This is also the cause of a lot of the canted front sight bases you see.
Also, as someone who used to be notorious for over tightening, applying much over 30 ft lbs or so of torque to a muzzle device can stretch barrel threads, mildly constrict the bore, and harm accuracy. This probably wonât be noticed by 99% of shooters but the effect is real. That âlast little bitâ of torque to line up a muzzle device can skyrocket your overall torque on the threads. It is way better to back off and switch shims, or even muzzle devices, around to get them to line up. This was so much of an issue that Surefire came out with a purple âhalf valueâ shim a few years ago. The purple shim will generally allow you to split the difference between over and under indexed.
Iâd wager that a very large number of rifle out there have barrels that are shifted one way or the other in the barrel pin alignment notch. Itâs probably not a big deal but it isnât a good thing either.
Oh shit, youâre right sorry. Iâm so used to people refering to the potential twisting of the upper and didnât read your post carefully enough.