I want a 7 or 8 inch upper, but what caliber?

[Gump]

I am gonna get (or assemble) a supershort upper for my SBR, but I'm concerned about the ballistics of 5.56 in a 7.5 in barrel. Now I'm leaning towards the 6.8SPC. Does anyone have the ballistic info on both of these calibers in such short barrels?
Also, who else beside Noveske makes 6.8 barrels this short?
Thanks
GUMP

[Tspeis]

Hands down, 6.8mm SPC. The 6.8 round performs exceptionally well out of short barrels.

As far as manufacturers who offer barrels that short, LWRC offers a complete 8" gas piston operated AR as well as 8" upper receiver kits. I couldn't give you any factual ballistic info, but one of the LWRC LE reps told me their 8" AR in 6.8 has better terminal ballistics at 100 meters than a traditional 14.5" 5.56 AR has at the muzzle.

Here's a pic.
http://www.gec-intl.com/LWRC-16.jpg



Tspeis

[istayapi]

I would have to agree with Tspeis, 6.8 out of an 8" brl 100 yards down range has more energy than the 5.56 out of a 14.5" at the muzzle. (quoted from LWRC website). I just ordered my 8" today :D

[tkoglman]

I would say go with the 6.8 or a 9mm. Obviously the 9mm won't give you the performance of the 6.8 but it will have less muzzle blast and be a lot cheaper to shoot.

[vinesr6]

Noveske has both 7.5" uppers (5.56 or 6.8).