Oops problem city today with the 612! Took her out for a break in, seemed like timing/interrupter is off. A live shell would spit out the bottom while the new one is being chamber (lifter is still up) !
Don't think I want to monkey with this issue, it is going back to CZ next week!!!

****ETA**** Sorry my bad! found out the problem was the extended mag tube nut didn't completely hold the barrel tight in place, disrupting the timing sequence. I left the original text in place just in case you run into similar problem after adding mag extension.