Hello Vent O Later.. I got into a 6.8 SPC a couple years ago. I was wanting an AR based cartridge that would come near the take down power of my .243 bolt gun. I wanted a cartridge that would perform well from a 16" carbine since I prefer them for calling. This need ruled out the .243 WSSM, since it likes longer barrels, and I don't.
I'd known of the 6.8 SPC for some time but wasn't initially impressed with it's ballistics until I revisited the 6.8 as it had become the 6.8 SPC II. I read that further developement of the cartridge had added more freespace in the chamber resulting in higher velocities before pressure signs showed up. I could now expect over 2900 FPS shooting 85 grain bullets. Some had even reported getting over 3000 FPS using the best chamber and barrel twist specs. 85 grainers form my .243 are running at 3100 so the 6.8 seemed to hold promise.
I went with a stainless 16" 6.8 SPCII recon profile barrel from Bison Armory. It has a 1-11.25 twist. Ben at Bison Armory installed his barrel on a RRA upper receiver I sent to him. He also provided a YHM free float forearm, low profile gas block, and a bolt headspaced to the new barrel.
I've mostly shot 90 grain Sierra Varminters, and Speer TNT bullets through my rifle. I load them into SSA brass, and seat them to 2.285 OACL. I've tried H-335, H-322, and RL-7 with H-335 and RL-7 givng me the best results. I'm getting 2775 FPS using 28 grains of RL-7, and 2880 FPS using 33 grains of H-335. My gun seems overgassed with the H-335 loads ejecting to 1 oclock. It works much better with the RL-7 load and ejects to 4 oclock. I don't see any pressure signs with either load, but just feel I'm about maxed out with my particular gun. In the time I've had this rifle I've probably shot near 500 rounds through it without a single malfunction. I'm getting under MOA 5 shot groups with both loads.
Hope this helps. Coyote 6974
