Has anyone tried this ammo? A 21gr bullet zipping along at 1850 fps looks interesting and would be pretty darned flat shooting! Any idea how the accuracy is with current rifle/pistol twist-rates?

They hit with some power but they are not accurate at all.

Not very accurate in my Cooper but we are forced to use them here in CA.

That's true. They are not very accurate. But, according to my gunsmith, who employs four full time gunsmiths, it's because one needs to remove all the lead buildup in the rifling before using it. Then your rifle, or handgun, should shoot well. Haven't tested this myself, but it does make sense, and I've always found that he knows what he is talking about.
The trouble is that once you clean the gun, you must do so whenever you shoot any lead ammo..... E

Trialed 1 box in a variety of guns. Accuracy was disappointing in all of them, even the plinkers.

They're all over the place. But I've only tried them in a Marlin M-60.