The pressure on most any rifle cartridge bigger then a 22 is greater then that of a 410 ga Id assume, but I wasnt sure what the chambers of a modern 410 could handle safely. So my 303 thought is out of the question obviously. I do want to start small(22 hornet) and go with the monobloc. I still am not sure on how to regulate the rifle, maybe lazer lights down the bbls and see where they are on the target @ 75 yrd and 50 yrd? I will need to read up on that before anything. I have a lot of old barrels from the familys shop back home I can test it on luckly! Thanks, CMW