what is the rifle? your certain its a 357/7mm super mag? no stamping on the barrel? did you measure the bore?
RR

I don't think its a7mm whisper cause it has a rim. Im thinking it is a 357 maximum necked down to 7mm. The gun is a BSA Martini rifle with a1.125 inch diameter barrel. I made some cases out of 357 magnum but the neck is too short.

no stamp on gun bore is 7mm.

no marking on barrel bore was slugged its 7 mm

and it has a 357 mag bolt face? let me do a bit of reasearch.
RR

Gun is a BSA martini rifle with a 1.125 inch diameter barrel. Cartridge must be rimmed. Bore was slugged its .284/7mm.If you use regular .357 brass the neck is too short when you fire form .

357 maximum perhaps?
RR