I've been shooting the Remington 6.8 SPC for approximately 4 years now. I've had 7 different uppers from which I have tested pretty much every bullet/powder combination available. I have put this thread together to help and better inform current users and potential buyers understand what the 6.8 SPC is and what it isn't.STRENGTHS:
1. 0-600 yard Combat Cartridge.
2. 0-300 yard Hunting Cartridge for small to medium animals.
3. Ideal LE/SWAT/HD Cartridge.WEAKNESSES:
1. Not a long range cartridge. This is mainly due to the lack of high BC bullets.
2. Still no affordable Plinking Ammo available. Not a cartridge that I would take to a high round count class, unless you can use handloads.BARREL LENGTHS:
The most popular barrel length is the 16" barrel. The 6.8 SPC is a very efficient cartridge as it uses the medium fast powders from H4198 to H335. When going from a 16"-20" barrel, you will generally see 75-125 FPS increase. Since the 6.8 SPC is such an efficient cartridge, the 18" barrel is the longest I would recommend. Here are the best Barrel Length/Gas Port Locations:
14.5"-below: Carbine Length Gas System.
16": Mid-Length preferred. Carbine Length Gas System, if properly gassed is OK.
18": Mid-Length pretty much a must.
20": Mid-Length and Intermediate Length preferred. Rifle Length will work with the slower powders, but may short stroke with the ever-growing light powders/fast powder combinations.TWIST RATE:
Twist Rate has very little effect on pressure when compared to the Chamber and the Land to Groove Ratio.CHAMBERS:
The 6.8 SPC was designed as a Combat Cartridge. One of the most important things about the AR is reliability, especially if you plan to use the 6.8 SPC for serious work. The SPCII and 6.8x43 Chambers are reliable and very accurate. The SPCII and 6.8x43 Chambers have a longer throat which allows you to shoot the hotter loads without worrying too much about pressure signs. For anyone that has a SAAMI Chamber, the one thing you could do is have someone lengthen the throat to the Improved Chamber specs.
Remington 6.8x43 SPC-(SAAMI Chamber):
Has a .050 freebore, 45 degree cone angle, .278 diameter freebore.
6.8 Remington SPCII (SPCII Chamber):
Has a .100 freebore, 45 degree cone angle, .278 diameter freebore, .3085 neck.
Has a .095 freebore, 45 degree cone angle, .2775 dia, and a .3085/.309 neck.BARREL GROOVES:
This, along with the proper chamber, is one of the most important ways of reducing the pressure. The best are the 5R, 3-Groove, and Polygonal barrels followed by the 4-Groove. The 6-Groove is OK.COMMON SPECS:1:10"/6-Groove/SAAMI Chamber:
The original specs.1:10"/6-Groove/SPCII Chamber:
This combination allows for approximately 75 FPS over the 1:10"/6-Groove/SAAMI Chambered Barrels.1:11"/4-Groove/SPCII Chamber:
This combination allows for approximately 25 FPS over the 1:10"/6-Groove/SPCII Chambered Barrels.1:12"/3-Groove/6.8x43 Chamber or 1:11.25"/5R/6.8x43 Chamber:
This combination allows for approximately 25 FPS over the 1:11"/4-Groove/SPCII Chambered Barrels.EXAMPLES OF MAXIMUM LOADS FROM SSA USING THE BARNES 85 GR TSX:
1:10"/6-Groove/SAAMI Chamber: 2950 FPS.
1:11"/4-Groove/SPCII Chamber: 3003 FPS.
1:12"/3-Groove/6.8x43 Chamber or 1:11.25"/5R/6.8x43 Chamber: 3050 FPS.MAGAZINES:
The 6.8 SPC uses its own dedicated magazines. You can load 5-8 6.8 SPC rounds in a 556 magazine, but after that, the magazine will begin to bulge. The three main 6.8 SPC magazine manufacturers are Barrett, C-Products, and PRI. All three are different in price and allow for different COAL.Barrett Magazines:
$40-$50. Available in 30 round magazines only. They are approximately 1" longer than standard USGI 556 Magazines. The max you can load your ammo in the Barrett magazines is approximately 2.260", which is shorter than the C-Products and PRI. Best used in Tactical applications due to the length of the magazines.C-Products:
$12-$15. Available in 5, 10, 17, and 25 round magazines. The 5, 10, and 17 rounders have straight bodies, while the 25 round magazines are curved. These are very reliable and affordable except for the 17 round mags, which are very problematic. The C-Products CS Springs can be a little weak, so it is recommended that they are replaced with the ISMI or Superior Shooting 556 30 round magazine springs for the best reliability. The max you can load your ammo in the C-Products magazines is approximately 2.285". With the ISMI or Superior Shooting Magazine Springs, they are the best bang for the buck of the 3.PRI (Precision Reflex, inc):
$30-$40. Available in 5, 10, 15, and 25 round curved magazines. The 25 round magazines are similar in length to the 556 30 round magazines. The max you can load your ammo in the PRI magazines is approximately 2.305". The PRI magazines are very popular with the 6.8 SPC Precision shooters who like to load their rounds longer, for increased precision.MUZZLE THREADS:
The most common muzzle thread for the 6.8 SPC is the 5/8x24, so any .308 muzzle device with the 5/8x24 threads can be used. Stag uses the 1/2x36 muzzle threads, which is the 9mm muzzle thread.