Studying caseless ammunition history each time I
May someone explain how this stuff works. The drawing on the left has a rim and a “burning-out bottom” implying that the gas would escape backwards. The rim holds the whole round in place. Then how does this cartridge leave the barrel?
Perhaps rim becomes a sort of driving band, as (usually) seen on projectiles 20mm and above?
The Italian 9mm AUPO semi-caseless also has a slight rim. On my specimen the rim is 0.362" and the base is 0.354". You can see it in the cartridge of the month section. Noticing the similarity of the round on the right made me think to check my 9mm AUPO. I don’t guess I had thought about it having a rim until just now.
Here is a sectioned view of a 9mm AUPO next to the drawing for comparison.
In German cartridges (in general with same design) rim used to hold cartridge in chamber until gas pressure will rise enough to collapse rim and move bullet forward. I think it was used for same purpose.