Re: mkII stuff
I use CCI Standard velocity target in the blue box. In my .22LR's it shoots functionally identical to FGMM.
Maybe it's not the piece-de-resistance of rimfire ammo, but it's affordable, relatively available, and seems to be pretty consistent stuff.
As I've emphasized here often, training equipment needs to be reliable and consistent. The level of its performance needs to be a given, a constant, so the only real variable is the day's human marksmanship performance. Perfection is wasted on such a task. Consistency, at whatever the level of performance, is the goal. Economics and ease of supply are far more valuable to the task than wringing the last ounce of excellence out of a temperamental and pampered steed. Any facet of the task that may cause hesitation in pushing the <span style="font-style: italic">shooter's</span> limits is counterproductive. Too much concentration gets expended seeking perfection, when simply gauging current proficiency and improvement is what we're really benefiting from.
Greg