FWIW, I have a Model1Sales upper with 6.8mm 20" chrome-lined heavy barrel (1:9.5")l from late 2004 with a Troy fold-down front sight gas block & the "A3" upper.
This particular specimen tolerates, without apparent pressure signs and with rounded primer edges, a load of
115gr Rem FMC or HP
Rem 9 1/2 primers
28.4 gr H322
(I worked this load up before data was available. I now load about 27.6 gr to avoid putting too much faith in the arcane science of pressure estimation via examination of spent cases.)
As a complete rifle, with scope, it tips the scales closer to an M1A than an M4gery. I have an Xtreme upper on order from Titan, placed a couple months ago to address this (among other issues).
I can't decide if I should retail-off my M1S upper or get on the list to use the reamer to open up the chamber to the newer dimensions. Any thoughts on the newer chamber with the unnecessarily fast twist (1 in 9.5")?
I have an M1 16" barrel. I have been considering going SBR or a suppressor, or both, and am in line for the reamer. Waiting for an upper to come in to complete my cardinal barrel. Any one have any experience doing either with the M1 Sales?
Getting in line with Paulosantos for his SPC II reamer is an inexpensive and easy way to alleviate some pressures from your tight M1S barrels' SAAMI chamber. You could work up loads like David did watching your brass, or stick with the commercial off the shelf 6.8 ammo.
We always tell shooters who already have M1S barrels the SPC II chamber reamer will help, but the over fast twist still limits you to off the shelf ammo, or careful reloads. Lowering pressures some definitely is easier on your rifle's mechanicals, especially your bolt.
For those considering M1S barrels or uppers, we tell them to look at other alternatives that have the SPC II or DMR chambers, and 1:11 or 1:12 twist. There are many available that are great values. These alternatives to M1S allow use of SSA's Tactical loads, warmer hand loads, and some of the newer higher performance 6.8 ammo that is in the works.
Some of you who have 6.8 uppers already, can just change out barrels at some point since you already have everything else. You can buy Xtreme barrels and Bison barrels for example.