Varminter.
Ok, Ok my reason for the 257R was because the 25-06 is not very efficient and over-powdered. I wanted something to duplicate my 25 Hunter and the 257R will do that. I have reamers for the 25Hunter but case forming is a lot of work and this cartridge operates at psi that Handi's don't like. With the greater powder capacity of the 257R I get nearly identical exterior ballistics.
The 257R is a lot more suitable for the Handi than the 25-06, unless you throttle down the 25-06 it will frustrate. The 257R will produce 3100ft/sec @ 50Kpsi with a 100gr bullet.
Now to the 7mm Waters a very nice cartridge and like the 257R a standard
loading. I suggest a Douglas standard chrome moly barrel with a 1-10 twist or if you get get it a 1-11" twist. Max bullet weight 140 gr.
I doubt you can duplicate the fusion weld for the barrel stud. Welding with any other method will ruin the barrels accuracy. There is no room on a factory stud for screws. I made a stud on the lath and fasten the stud with two 10x32 screws 5 threads and J-B Weld.
My 257R with a 24" octagon barrel is so well balanced that I can't even think of a better length. My 25Hunter bolt guns have 23 and 24" barrels.
Many of the high grade Eurpean SS break open rifle have 24" barrels because of the fine balance they provide. I am talking about sporter barrels not bull barrels.