6x51R

[JDHasty]

It’s rimmed 243 Winchester.  Three fire formed cases and three dummy rounds made using culls w/87 grain V-max bullets.  The cases are made from 444 Marlin parent cases from Starlinebrass.
I have been posting on my CPA Stevens project here.
https://www.rimfirecentral.com/threads/cpa-stevens.1339033/

There is more on how I formed the cases posted in the link under the thread here on my C.C. Johnson 219 Donaldson Wasp 44-1/2 Stevens. 

[MeatMissile]

Is that a 307 necked down to 6mm?