I like the 15 LB spring and like I said, one with it is reliable with Wolf/Tula the other has about 5% light strikes. I KNOW it is 100% with federal, and need to try CCI - but I'm sure I'm OK there as well.
I actually find Tula surprisingly high in quality. I actually don't like it for the AK, but at less than $160 shipped and reasonably clean, its a good training round - and if I have an occasional light strike, even better for practicing what the DA was meant for - follow up.
OTOH, my guns are getting slick enough that the 18 LB spring might also be fine. Just followed pages 1,2 and 7 on the sticky thread and my new UG/SR is VERY nice - nicer than any OTB Legion at least in DA. (SR Kit also).