I do my primer pocket uniforming with Sinclair's primer pocket uniformer. I use this tool on the RCBS case prep center or with a hand drill until this uniformer bottoms out (no more brass shaving are seen). Even on the "treated" cases these S&B SR primer sit slightly proud/flush to the case head. Wolf, Winchester, and CCI all seat perfectly with or without using the uniformer.
I know S&B are well known for having shallow primer pockets on quite a few of the rifle rounds like 7.62x54, .303 British and I think 8x57 Mauser were some of them. I have not heard of their primers being overly long though.
Winchester has had S&B make some of their ammo for them and I think they had some runs of primers made too. If your using a brass colored primer from Winchester then it very well may be made for them by S&B.
This SAAMI diagram You must be logged in to see this link. states at the bottom "Primer to be seated flush to 0.008" below face of cartridge case head" I've shied away from flush because of my obsession with milsurps and free floating firing pins. These S&B primers were mostly flush, so according to SAAMI, maybe I'm just overly cautious?
Free floating firing pins don't have enough mass to cause slam fires. Worst case is a tiny ding in the primer. As long as the primers are flush you are good to go. I've used all kinds of primers in my reloads and never had any problem; not even with soft primers. The only way they can cause a problem is if they get stuck forward in the channel and as long as you keep the bolts clean, that is extremely unlikely to happen.
OGCA Lifer,NRA Life member, son of a 325th GIR Glider Rider