LRRPF52 Wrote:I've seen that with some collared muzzle devices that time up to a small shoulder, which yours appears to have. A muzzle device doesn't need a lot of torque on it, and TBAC recommends just barely snug, with Red Loc-tite to secure it in place for the brakes.

As long as your barrel is cut by someone competent, who can cut square and true threads to the bore, with the threads concentric to the bore, using TBAC's relief cut, you should be golden. A shorter barrel will balance out better with the can as well. What length are you thinking about?

mwilkins Wrote:Spoke with my smith today. I wont lose any length off the barrel and most of the crown will stay in tact if all works out. With the current thread being 3/4x28, we will be going to a smaller thread. 5/8x24 is first up. if the 3/4x28 threads are too deep to get a good cut for the 5/8x24 then he will drop to a 9/16x24 thread. This is not his preference due to the metal getting pretty thin around the crown and bore for a 6.5 caliber round. If that comes to light, then we will discuss cutting the barrel back at a last resort but at least for now there is a little glimmer of light. Will be sending off the barrel this week. Should be able to get it back sometime later next week.

LRRPF52 Wrote:Every AA Grendel I have seen has a 9/16x24 thread pattern, with a shoulder. The FAL uses 9x16x24 LH, and this was because the FAL had a very narrow barrel profile as a service rifle, while still needing enough shoulder to support a washer for muzzle devices.

The Grendel thread pattern was determined during the Clinton Assault Weapons Ban period, when the 6.5 Grendel was cutting into new territory with larger calibers in the AR15. The Colt 7.62x39 Sporter II used 1/2x36 IIRC.

Knight's Armament uses 3/4x24 on the SR25/M110/Mk.11 series.

Eagle Arms/ArmaLite Inc. started using 5/8x24 on the 1996-forward AR10.

DPMS started off using plain target barrels without any threading on the LR-308 series because they were developed during the ban as well. After the ban, DPMS started using 5/8x24 threads, like ArmaLite Inc.

There was no thread pitch standard for AR10's, and still isn't to this day. There certainly wasn't and isn't a standard thread pitch for larger bore calibers in the AR15. The 6.8 uses all sorts of different thread pitches from maker to maker, ranging from 1/2x36 for Model 1 Sales, to 9/16x24, to 5/8x24.

There is a discussion of this briefly in Volume II, covering basically what I just said, with the historical context of the Clinton Assault Weapons Ban underlying the technical aspects of thread pitch choices that several manufacturers went with. I don't think I've seen 3/4x28 on a Grendel though. Maybe Bwaites or LR1955 have.

Variable Wrote:I have a factory AA 19.5" that was originally threaded 3/4x28. It's a Lothar barrel.

BluntForceTrauma Wrote:Back at the beginning — I wanna say 2004 —AA's sniper-style rifles were threaded 3/4x28. It would have been their GDMR model. Bill A. did this to have as much meat at the muzzle as possible.

LRRPF52 Wrote:There was no thread pitch standard for AR10's, and still isn't to this day. There certainly wasn't and isn't a standard thread pitch for larger bore calibers in the AR15. The 6.8 uses all sorts of different thread pitches from maker to maker, ranging from 1/2x36 for Model 1 Sales, to 9/16x24, to 5/8x24.

motoxxx_ryder Wrote:thats because they need to standardize the 308 cal AR platform first LOL. theres what AR 10, and then the SR 25 which parts are not interchangeable. Someone needs to cave and create a benchmark standard for the platform.

LRRPF52 Wrote:There is much more than that. It basically would take a funded paper to document all the AR10 variations on the market. I did a thread on it on AR15.com, covering most offerings from 1955 to present. There are around 40 different AR10 and AR10-type rifles that have been manufactured, many of which have their own unique data sets, even within manufacturers.

For example, DPMS has no less than 3 different upper receiver rail heights, and a new GII design that departs entirely from the LR-308.
ArmaLite Inc. has several different receiver types, starting with no forward assist, the FA, then a receiver set that will take SR25 mags, whereas their first receiver design took modified M14 mags, which have undergone at least 3 generations of evolution themselves.
At least half of the 40 different AR10-type rifles do not share receiver interchangeability, pin compatibility, and other important considerations with the mechanical engineering of the bolt carrier travel and deconfliction with the receiver extension threads.

Charge handles, magazines, upper receiver threads, ejection port doors, extension tubes, buffers, recoil springs, gas tube lengths, operating systems, and many other aspects of the guns are all over the map. There isn't and never will be a standard for the "AR10" or derivatives of that design.

The new wave of AR 308 economy receiver sets only exacerbates this problem, and many of the build projects are non-functional from the start, for a number of reasons. They usually boil down to parts that were never meant to work together, defective parts, and really bad chamber reaming on barrels.