yes I know this but it works only in mauser 71 actions. had to make some ammo for an old combination hammergun - 16 ga shotgun barrel and a special 11,15x54R rifle barrel. was simply a 60 mm case cut down to 54 mm, there are trillions of different wildcats bases on the 11 mm mauser case.
first I made brass from cheap 300 win mag. was simple because you cut it under the 300 win mag shoulder so there is no need to open this up. ammo don't work because the extractor of the combination gun was not taking the much smaller rim. the M 71 extractor works different and grab behind.
I have some 300 win mag brass here, its anealed and will make a black powder fireform load. open up the neck on this case is pain in the ass. I know it from making a lot of 300 11,2x60 schüler cases from 300 win mag.
26 work steps with each cases and a lot of them were for open up the neck.
but I lost only 10 of the 300, thinking this was not bad.