This is a brass cased version of the familiar 410 shotgun shell. While it can be loaded with birdshot, it is ideal for the Lee-Enfield rifles that have been converted to a smoothbore 410. This should not be confused with the 303 based “410” but for the Singapore ones that are meant for the 410 shotshell. The inside neck diameter is 0.435 and a 0.410″ round ball can be loaded in the case and crimped in place. It will need to be supported by wads and a roll crimp on the mouth of the case.