I use to sell them... I still have a few i kept for myself... Anyway, they came in 22LR and 22WMR. They also came in two lengths, and in "std." and "extra".
I was told by Dieter Krieghoff that the "extra" models were test fired at the factory and were more accurate than the std. ones. Basically, "hand picked", BUT that doesn't mean a "std." one couldn't be just as accurate, and just wasn't hand picked from the pile.
Mine are very accurate, and always come back to zero when reinstalled.
DM.