Please advise sizes of mandrels to use for the above task start to finish ! or Just how to get the best results for this job
Thanks

Depends on if you have other calibers of various sizes you load. If you load a 358, 375, 416 (or 40 something), 458 and obviously the 50-95 dies, you can step your way up. If you go the route of buying the dies from RCBS to do what you want, it will be very expensive. I believe that Redding has a less expensive set of plugs that fit at least their dies. Some even fire the case loaded with corn meal or such but that may a little dicey in a M76. I suggest that you to to the CAS City forum. They have a M76 forum there and there is a lot of info on doing just what you want. Look in the sticky archives.

fireform or contac tbutch lambert for a set of dies

Thanks guys I steped my way up next is fire forming !