 This allows cartridges of a length impractical in other designs; as well as easy use of caliber conversion sleeves.It is common to find conversion sleeves for double barrel shotguns, allowing the firing of smaller gauge shells as well as sub-bore rifle cartridges (and thus allowing the same gun to be used with, for example, 10 through 28 gauge, as well as .410 bore shells).The break action design is best suited for non-repeating firearms.