4200M -- (1) the bolt-face of the Model 7 isn't large enough to safely convert to the Lazzeroni Patriot cartridge - I know some have been converted (along with 700's) but I don't think the safety margin is there and (2) I had a Lazzeroni Patriot, a custom job built on the Lazzeroni action which was plenty beefy and in my rifle 165gr and 180 bullets developed velocities in excess of any I've seen (over a chronograph) from the .300 Win Mag - mine had a 23" barrel.
My favorite was the 165gr bullet as with the right batch of RL15 I could run it up to the point it was approaching Weatherby-country with a shorter barrel and a lot less powder. Case life was excellent with nary a blown primer -- I considered a load safe if, after 10 shots and annealing every 3rd shot, the primer pockets were still tight and I didn't need to do excessive trimming.
As an aside I also had the first Lazzeroni Hellcat (.375) that Lazzeroni built --- basically a 30-ca; Patriot case necked up to .375.
Again with the right batch of RL15 I could run a 300gr Nosler pretty close to 2600 fps -- over more than one chronograph - without pressure problems. I normall shot it closer to 2525 fps because my rifle was fairly light and above 2550 it wasn't pleasant for me to shoot. A lot of .375 H&H factory ammo lists 300gr velocities in excess of 2500 fps but, and I haven't chronographed them all, the ones I have tended to be between 2550 fps to 2575 fps.
The only problem I ever had reloading them was finding a good batch of RL15 and being able to buy enough of it.
