6.8 SPC Upper What Brand?

[OutlawDon]

Awesome looking build and good info.

How's the inherent accuracy/downrange power of the 6.8? What's the effective range from a 16" barrel?

[M9er]

R.R.A! you cant go wrong with this company. Excellent Upper's

[Desert_AIP]

R.R.A! you cant go wrong with this company. Excellent Upper's

RRA makes a quailty product, but they are using the old spec barrels on their 6.8 rifles.

They have changed to SPCII chamber but still in 1/10 twist.

Current spec is no tighter than 1/11 which is needed for maximum performance of this round.

With 1/10 you'll see ~ 100 fps slower with all rounds and can't maximize handloads due to early pressure signs.

[sholling]

Awesome looking build and good info.

Thank you. I finished her just in time to get in one range session before Inland F&G closed.

How's the inherent accuracy/downrange power of the 6.8? What's the effective range from a 16" barrel?

I can't speak to inherent accuracy directly because I've never had a chance to find out. I got it sighted in and ran out of time. Mine has a lapped Lothar 1:11.25 twist polygonal barrel so I would expect it to do well for a chromed bore barrel. Chuck Hawks did an analysis of the 6.8 SPC and 6.5 Grendel and felt the only thing holding back the 6.8 from match use was the lack of .277 match bullets. Most .270 caliber rifles are hunting rifles.

As far as 16" vs longer I can only pass on second hand info. My understanding is that because the 6.8 SPC was designed for 14-16" barrel rifles it's within 50 fps of maximum velocity at 16". I haven't tested that so take it with a grain of salt.

Here is a comparison of a fairly heavy bullet in a mild 6.8 SPC factory loading against 5.56 and 7.62.x51. Note that this is from a SAAMI spec barrel and a more modern barrel and capable loading should add 100fps or more at the muzzle.

[ar15barrels]

Here is a comparison of a fairly heavy bullet in a mild 6.8 SPC factory loading against 5.56 and 7.62.x51. Note that this is from a SAAMI spec barrel and a more modern barrel and capable loading should add 100fps or more at the muzzle.

That's also from a 24" barrel length so expect to lose some velocity going back to a 16" barrel.

Here are my velocity tests with factory ammo from a few years ago.

https://www.ar15barrels.com/data/68velocity.pdf

Note that those were the original 2004 LE loads that were loaded so hot that all commercial ammo was eventually loaded to be 200fps slower.
The lone lot of ammo on the bottom of that page was the commercial ammo.

[Purple K]

My Stag 6.8 with a 16" barrel has bee trouble-free.

[sholling]

That's also from a 24" barrel length so expect to lose some velocity going back to a 16" barrel.

Do you have similar numbers dropping a 5.56 from 24" to 16"?

[ar15barrels]

Do you have similar numbers dropping a 5.56 from 24" to 16"?

I could run quickload predictions, but I have never had the chance to test fire 12 different 5.56 barrels made from the same run of barrel blanks in all different lengths in one sitting like I did with the 6.8 barrels.

[SkyMag68]

stag's 7h would be better choice because its better chamber/twist rate...capable of handling hotter load..I recommend anyone interest in gettin 6.8 upper to check out http://www.ar15performance.com/ my 6.8 upper from them.

[lunchb0x]

Well just to throw out another option there's Bison Armory... Ben has great customer service and really good prices to boot. There are quite a few guys on 68forums.com that are shooting sub-moa groups with his products/builds.