Ok, I did a search for DMR-C and found no results. I fount that odd. Ron's correct. There are a few differences between these two barrels and chambers. Both are nicely spec'd barrels though.
Can someone please tell me which is "better" or what the appreciable differences are in these chambers?
DMR is the proprietary match 6.8 chamber designed and offered by AR15Performance. It's also used by Titan Armory. It is a high performance design and works well with all 6.8 amunition power levels including hotter handloads. The DMR-C is the version of the DMR chamber with tolerances built in for chrome lining.. hence the C.
The SPC II chamber is the improved version of the original SAAMI chamber with an additional .05 leade for a total leade of .10 which reduces pressures and allows the use of higher performance ammuntion. This is the chamber most of the industry has moved to in replacement of the restrictive SAAMI chamber.
I have been juggling the idea of a Bison Armory upper (because I like E.R. Shaw barrels) and on from AR Performance. The only difference I've noticed are the chamber styles. Anyone shed some light?
As Ron indicated, there are some differences. The XT is more of a custom production barrel designed specifically to maximize 6.8 performance with some additional features:
The 6.8 XT is an affordable upper half with all the right stuff. We used the same match style throat as in the DMR chamber but, with a combat reliable chamber size, a 16" Nitro-Carburized 11.25" twist barrel with modified 5R rifling and other upgrades not found on most production rifles. The lightweight contour is .700" under the guard and .600" from the GB to the muzzle. This basic model has mil spec. plastic handguards with heat shields."
Bison Armory: " 416 Stainless Steel
SPR (18") and Light SPR (16") profile
Ops Inc model 12 suppressor collar shelf
SAAMI Spec-II Chamber
4-groove, 1-11" twist
M4 feedramp barrel extension
Mid length gas system"
The ARPerformance barrels like the XT and RECON are pretty much hard use custom barrels, and Bison barrels are very good production stainless steel barrels. It depends on your use.