I use 0.311” in my .30’s. Even .30/30.
I’ve used both the Lee 120gr RNGC and 113FNGC in my .30/30.
As I type this, I have about 120rds in a large Folgers coffee can, loaded in the basement. They’re loaded with 7.5gr of GreenDot. Chrono about 1,350fps.
My M1894 Win AE XTR w/Williams 5D receiver sight is sighted +2”at 50yds. Shoots 1”groups.
I’ve used 30.0gr of RL15 under the 120gr RN for 2,200fps.
I crimp lightly into the bearing surface like the .30carbine. But, I have crimped into the forward edge of the forward lube groove.
My Marlin/Glenfield M30 w/Microgroove bbl loves both at .311”.
My favorite however is the Lee 150gr FNGC. My old 1970’s vintage Single cavity mold casts to 160gr. Has thinner lube grooves. I gave it to my older brother in the early ‘80’s. It’s been to Alaska, Maine, Montana, New Mexico and Florida. Bullets cast from it have taken Mule deer, white-tails, Moose!, snowshoe hares, cottontails, jack rabbits, ground squirrels, tree squirrels, grouse, even an upstate NY black bear. Mostly over 7-10gr of Unique, otherwise 28.0gr of IMR3031. Either unsized w/tumble lube (unique loads), or Sized and gas checked and sized to .309” with an old hand push-thru Lee sizer.
I now again hold it. But, I bought a newer 2-cavity version l like better. It has slightly wider lube grooves and cast to 158gr w/Hornady crimp on gas checks. It’s really the only bullet you NEED for a .30/30.
I have a 170gr version. I don’t like it as much as the nose is long enough that when crimped to the lube groove it causes some drag cycling through my l/a .30/30’s.
I do strongly recommend you get a Lee factory crimp die. Crimp after seating for best accuracy.
Forgot to mention I had a Savage M340 back in the early’80’s. It shot really well with cast bullets!