Scorch:An Old Master told me to use a cotter key for the solder-in trick.Nice flat side for the solder joint.His name was Ben.
On the mag stack thing,ideally the mag box width /taper is such that the cases will stack as an equilateral triangle at both the casehead and the shoulder.
It has been my experience putting a 308/243 in a mauser box that,due to the straighter case,the shoulder will stack to a tight triangle between the box.follower,and rails while while back at the case head,the stack is loose.Its not tight up against the rails,and the brass at the case head sags down.
Then the bolt coming forward over rides the case head,but digs into the case body,crushing the case as it pushes the cartridge forward.The case head is not on the bolt face,its under the bolt,and the bullet/neck are jammed into the feed ramp.
You don't have this option,but,IMO,the best way to put a.243 in a Mauser is to use a 6mm Rem chambering reamer and make it into a necked down 7x57 Mauser(which is what the 6mm R is)
They really should alter the mag box to be a little wider at the shoulder for the .308 cartridge family to stack properly if they are going to chamber these cartridges in a Mauser.
I'd have to do some number figuring to see how much material would need to be milled off the boxwall to make a Mauser box correct for a .308 parent case.