I know that some folks have made .410 shells from .444 Marlin brass. I happen to have a few spent .444s that I’d like to make into brass blanks for bird dog training. Ideally I would like to use AA7 as I have plenty on hand but I also have Unique and quite a few others. This is unlike any loading I have done in the past and I have never loaded blanks. I know that the rims may need to be thinned to fit the shotgun (break open single shot) but I have also read that some folks say the flash hole needs to be opened for successful blanks as well. Not sure if this would apply to these .444s or if I will just need to try a few to see if it’s necessary. Would cream of wheat be an acceptable “payload” packed in with an over shot wad?
Any suggestions would be welcome and I appreciate any guidance prior to embarking on this new endeavor.