Re: Ring slippage
Recoil velocity is approx 12 ft/sec and recoil is 29.5 ft/lb. (that's without a brake)
If you take the rings apart, double check that there is a gap, and check that the screws aren't pulling up the first thread out of the bottom ring, interfering with the top half tightening down if there's only a couple thou of clearance. The rosin is a good suggestion.
If you have a correct sized tap, I'd also check the bottom ring half to ensure that the threads aren't getting pulled out of shape. If they are, I don't know of a way to fix it other than going one screw size larger if you have access to equipment to do the job.