I just got some primed brass with Silver colored, Large Rifle Primers with a rather small capital B stamped bottom center. Any idea what brand/style these are?

That's how CCI marks their Benchrest primers. CCI has always represented their BR primers to be identical to their standard LR 200 primers but simply kept to closer tolerances.

Thankyou and that is welcome news as I use CCI-200 primers routinely!