Hello i have and old one of these and even with loads at 3200 the cases are ringed and the primer expanded and flattened any higher velocity than this it gets worse[3500] ,i have tried the same loads [3500]]with normal results in a tikka 22-250.The fellow i bought miroku from claims it has new barrel [and original miroku barrel as marked]is this a headspace problem,bad chamber? or some other ? thanks for any help on this !

I would say a head space problem.

How are you resizing the cases for the Miroku? IF there is a head space issue once fired cases should be ok if the shoulder is not set back when you re-size them. Of course if head space is REALLY excessive it will need to be fixed. You can "roughly" check head space with paper shims and a mic or dial caliper.

The brass is new,the 1st firing[ Norma]this rifle has seen a bit of use by former owner though.might get a gunsmith to check the headspace Thankyou Gents

The difference between the diameter of a .22-250 chamber and the brass is greater than most other rimless rounds. The .250 Savage parent cartridge used slightly smaller brass.