"They seem to function just fine in my Mark II's and 10/22's." +1 I've shot them from two 10/22's, one almost out of the box new, the other with well over a thousand rounds through it... Both cycled fine.

My guess is one of the reasons for the heavy bullet is to help keep pressure up to cycle semi-auto's.
In my particular guns the accuracy at 50 yrds wasnt the best. Actually, it was pretty poor. But that'll vary with the gun. Good luck.