I have shot a CZ 527 in .221, for several years now. Absolutely love the thing. The most accurate rifle I own, and I own a bunch.
My handloads with IMR 4227 wound up at the max recommended of 16.0 grs. Recent chronographing showed I was only getting 3050 fps. Most manuals show in the neighborhood of 3300 fps.
I have read many articles extolling the virtues of Lil-Gun in this caliber, so I bought a pound of it to try.
The Nosler loading data showed a max of 16 grs, with a velocity of 3384 fps. Pressure at 48,900 CUP.
I loaded 10 rounds with 16.0, ten with 15.5, and ten with 15.0.
The chronograph showed a bit over 3300 fps with the 15.0 gr. load, slightly over 3400 fps with the 15.5, and GASP, an average of nearly 3600 fps with the 16.0 load.
Primers had severe cratering with the 16.0 load, bad enough that I only shot five to test, will break down the remainder. These used (usually) hard CCI primers.
The 15.5 load still had mild cratering.
No cratering with the 15.0 load, easy extraction, and it met my velocity goal,so will stick with this one.
A full grain variance, in this tiny cartridge, is a LOT. Didn't expect this much variance, but another lesson in being careful. A chronograph also helps immensely.