12-31-2015, 04:03 AM
1. AA didn't make the 6.5 Grendel with 9/16x24 just to extract money from end users.
That thread pattern was decided on when there was no common thread, because the law forbade you from having threaded muzzle on AR15's, and it provided the best shoulder support for thinner barrel profiles on the light guns that would get permanently attached muzzle devices at the time to meet legality requirements of the Clinton Assault Weapons Ban.
Knights Armament, the first company to re-introduce a production 7.62x51 AR rifle, used and uses a totally different thread pattern on the SR25, namely 3/4x24 muzzles.
ArmaLite Inc. decided to use 5/8x24.
When the ban expired, DPMS started making guns with 5/8x24 threads. This was after AA had already introduced the 6.5 Grendel, done the testing, and was producing guns.
There is no standard for the .308 guns, and 6.5 Grendel is its own cartridge, so no big deal. A2 flash hiders from AA are $16.50. http://www.shopalexanderarms.com/Muzzle_...16-24.html
2. There are a few machine shops that make bolts to vendor specific requests. The 6.5 Grendel bolt has key differences that are specific to the cartridge. The AA hard Use bolt is made from a certain alloy, and has an Ion Bond process done to it to make the surface very smooth, which helps reduce the chances of microscopic fractures from developing for shooters who want to run a gun hard with high volume.
I personally have been using different standard AA bolts for years now, with a lot of load development where I will see pressure spikes in a pressure ladder, finding where my parameters are with a certain load range so I know where to look for the lower pressures that I would feel comfortable with mass-producing. I have yet to experience any failures of any kind. AA has stated that even the bolts they use in a pressure test breech for proof loads have not broken after years of constant testing.
The .136" bolt face depth is so a reliable extractor can be used that will have the groove size that is correct for the 6.5 Grendel's thicker rim, compared to a tiny 5.56 rim. Extractors are what fail regularly with .125" bolt face depths with 7.62x39 in the AR15.
If you get the metallurgy right on a correctly-spec'd bolt, and have a thorough quality control process, you will make reliable bolts that hold up, in any caliber, used within their design limitations. I've been shooting the AR15 since the late 1980's, and the only bolts I have broken are 5.56 bolts, that were run hard, like over 10,000 rounds.
3. Any AR15 upper is fine. I personally prefer a heavy billet receiver if the barrel will be heavy, but for the barrels you are talking about, a lightweight receiver is perfect. I have built several guns with both the AA 16" Lite Fluted, as well as the 18" Brownell's barrels, and a standard M4 or upper of your choice is the norm. The upper receiver is not a factor in containing hoop stress.
Biggest challenge with the Brownell's 18" MLGS barrel is that the gas port is cut way too big, so it needs to be choked with an adjustable gas block right off the bat, and a heavier buffer, like an H3.
The 16" AA MLGS fluted barrel works right out of the gate with no need for adjustable gas, and recoil is pleasant. For what you are doing, I would consider the lighter, shorter option, especially for HD.
My first Grendel barrel was a 16" AA, and I have really enjoyed it over the years. Supersonic reach for me at my altitudes has been well past 1000yds with factory 123gr ammo.
That thread pattern was decided on when there was no common thread, because the law forbade you from having threaded muzzle on AR15's, and it provided the best shoulder support for thinner barrel profiles on the light guns that would get permanently attached muzzle devices at the time to meet legality requirements of the Clinton Assault Weapons Ban.
Knights Armament, the first company to re-introduce a production 7.62x51 AR rifle, used and uses a totally different thread pattern on the SR25, namely 3/4x24 muzzles.
ArmaLite Inc. decided to use 5/8x24.
When the ban expired, DPMS started making guns with 5/8x24 threads. This was after AA had already introduced the 6.5 Grendel, done the testing, and was producing guns.
There is no standard for the .308 guns, and 6.5 Grendel is its own cartridge, so no big deal. A2 flash hiders from AA are $16.50. http://www.shopalexanderarms.com/Muzzle_...16-24.html
2. There are a few machine shops that make bolts to vendor specific requests. The 6.5 Grendel bolt has key differences that are specific to the cartridge. The AA hard Use bolt is made from a certain alloy, and has an Ion Bond process done to it to make the surface very smooth, which helps reduce the chances of microscopic fractures from developing for shooters who want to run a gun hard with high volume.
I personally have been using different standard AA bolts for years now, with a lot of load development where I will see pressure spikes in a pressure ladder, finding where my parameters are with a certain load range so I know where to look for the lower pressures that I would feel comfortable with mass-producing. I have yet to experience any failures of any kind. AA has stated that even the bolts they use in a pressure test breech for proof loads have not broken after years of constant testing.
The .136" bolt face depth is so a reliable extractor can be used that will have the groove size that is correct for the 6.5 Grendel's thicker rim, compared to a tiny 5.56 rim. Extractors are what fail regularly with .125" bolt face depths with 7.62x39 in the AR15.
If you get the metallurgy right on a correctly-spec'd bolt, and have a thorough quality control process, you will make reliable bolts that hold up, in any caliber, used within their design limitations. I've been shooting the AR15 since the late 1980's, and the only bolts I have broken are 5.56 bolts, that were run hard, like over 10,000 rounds.
3. Any AR15 upper is fine. I personally prefer a heavy billet receiver if the barrel will be heavy, but for the barrels you are talking about, a lightweight receiver is perfect. I have built several guns with both the AA 16" Lite Fluted, as well as the 18" Brownell's barrels, and a standard M4 or upper of your choice is the norm. The upper receiver is not a factor in containing hoop stress.
Biggest challenge with the Brownell's 18" MLGS barrel is that the gas port is cut way too big, so it needs to be choked with an adjustable gas block right off the bat, and a heavier buffer, like an H3.
The 16" AA MLGS fluted barrel works right out of the gate with no need for adjustable gas, and recoil is pleasant. For what you are doing, I would consider the lighter, shorter option, especially for HD.
My first Grendel barrel was a 16" AA, and I have really enjoyed it over the years. Supersonic reach for me at my altitudes has been well past 1000yds with factory 123gr ammo.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com