Any one up to a mk5 should do the job for you. A mk6 wont fit in as its bigger diameter. Regarding a query about hawk mk2 and mk3 parts that are the same, it is only really the trigger,sear,guard, piston + rings,mainspring all pins,cocking arm and screws. However you could interchange the cylinder and barrel/breech block. They are near enough the same gun. Check Chambers website and compare part numbers. I reckon you would do yourself a favour by not fitting the safety and use the sear spring from a Victor instead.I think its part no cs131 on the website but check first.