I finally made it out to the the range to test the CZ-550 this morning. I had loaded up a few rounds of the Lee Group Buy 275gr TC that were given to me by KTW. They dropped at +.382", I sized them down to .369" in one pass....talk about grunt! I wrapped them with two wraps of tracing paper. Mic'd at .3752 after drying. I loaded them over 68gr of IMR-4064 and a magnum primer. At first I was getting 50% success on seating until I flaired the case mouths a bit more and lube the patches with some JPW, then I had no further problems with patch tearing.
The second load was a Lyman 378674 over 64gr of IMR-4064 and a magnum primer. These were also donor boolits (NOT from KTW) but the quality of the castings was sketchy at best. Again sized to .369 and wrapped twice. With this boolit I stuck with the well flaired case mouths and JPW, no tearing problems.
Both loads grouped to the same point of impact and grouped roughly 2.0" at 50yds from the sitting position. I definitely think the loads can group better. I had a light sweat shirt on and the factory recoil pad. The recoil definitely got my attention.