Yes. 3031 has good case fill, and better insensitivity to being dispensed with small charge weight errors than some, so it responds well to being dispensed by volume. Works better with light bullets than Varget and the 4895's, IME. I have previously suggested people try 3031 and also try Reloader 10X for bullets 55 grain and lighter to see which one your gun likes better.
The 6½'s are thin and they are mild. I used them with mild loads of 4198 in .222 Remington for a lot of years and they did fine there, drilling many a cloverleaf. In .223 you could use them in a bolt gun for loads up to around 45 kpsi, but I would not push them beyond that. Good enough for .357 Mag and 9 mm loads, though, so if you have either you can shoot them up that way.
In the AR I would avoid the 6½ because the firing mechanism is made energetic enough for military spec primers at their lowest sensitivity limit (3 standard deviations from an already higher-than-commercial ignition threshold in a height drop test) plus about a 20% margin. That could be a hard on the light primer cup, not to mention added risk for slamfires. It's also not worth gas cutting your bolt face prematurely just to avoid getting something more appropriate.
These days you have three small rifle military spec primers available. The CCI #41 and Tulammo KVB556M are magnum primers and the Federal GMM205MAR (the last two letters making it distinct from their regular GMM205M) for a match standard strength primer.
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Last edited by Unclenick; January 20, 2013 at 12:09 PM.