BARREL EXTENSION TORQUE TRUTHS & TIPS

[JIM MILLER]

The Brownell Barrel Extension Torquing Tool, may be misnamed but is fully capable of being used as a Barrel Extension Torquing tool, up to 150 ft/lbs; as I have done repeatedly on both AR15 and AR10 platforms. Usually, when removing the original barrel extension from the barrel manufacturer for having both melonite processed (nitride); then replacing and indexing the gas port as needed in a mill.

The only prerequisite, is that the Torquing process is NOT inverted as suggested here, in using this tool for the barrel nut, but that the barrel is precision torqued by the tool. However, the barrel must be HELD IN A MACHINIST VICE (i.e., KURT 6") preferably mounted in a large Vertical Mill. HOW the barrel is held is equally critical. It requires a pair of mating custom aluminum blocks (about 3" to 4" long) with half-moon channels cut to the radius of the barrel where you can grip; but it is NOT precisely the radius of the barrel. It is slightly smaller, so that a smaller ball mill can be used to cut a second relief down the center of the radius reliefs, which leaves two contact points to grip the barrel so that no direct pressure is applied to the barrel 90-degree (in-line with bore) position. The same smaller ball mill is used to relieve the top mating OD corners of the original barrel relief channel, so that all you have left is these two (per block) pressure points. From an end view, the pressure points of the aluminum block would be at 10:00; 2:00; 4:00 and 8:00 o'clock. What you are avoiding is pressure at 09:00 and 03:00 o'clock, which placed the Kurt clamping pressure horizontally in line with the bore axis. When the Kurt vice clamps down through these blocks, it applies pressure NOT to the barrel's center, but above and below its center-line where it bridges the load above and below the bore. With the barrel firmly locked in place in the vice, with its "grip" blocks; then the TORQUE is applied to the barrel extension directly with the tool; 120 to 140lbs on AR15; 130 to 150lbs on AR10.

One last VERY important point, often overlooked by many: is that the threads must be liberally greased with 50W to 70W oil during assembly and torquing; NOT "Locktite" or any other "anti-seize" thread locking agent. The whole purpose of "torque," is to apply tensile strength to the threads and STRETCH THEM to a given load; not fool yourself with "glue" techniques into thinking you've aided in the thread adhesion surfaces. Leave the Loctite tricks to small screws that are too small to torque properly, and don't have bursts of heat during operation.

[98Z5V]

Go hit up the Intro Section, Jim, and tell us about yourself.

The barrel extension is intended to be installed, as part of the barrel manufacturing process, before the barrel is final machined. Doesn't even have the gas port drilled yet,  when the extension goes on.

Barrel extensions are not meant, or designed, to be removed and reinstalled.  The torque for installing during the manufacturing process is 175ft/lb.

[98Z5V]

The real reason that you're seeing torque numbers below what I'm stating is because - the initial operation has already been done.  The threads are already stretched, from the real install, the initial operation of building the barrel.

You're taking apart barrels, extensions, and applying torque (hopefully) to realign your extension with the feedramps that were cut in - a later barrel assembly process...  You are torquing it again, after the threads were torqued and stretched to spec the first time.  Your torque values that you are seeing are torque values from stretched threads...   and lower than spec, because of that.  That's the reason that you have a torque range, and not a direct number. 

Hope that makes sense. Look forward to your intro, in this section here (I'll link it for you):

This is the Intro Section, just click it, and make your post about you:

https://forum.308ar.com/forum/22-introductions/

Edited February 11 by 98Z5V