longrangehunter
Handloader
- Jun 19, 2011
- 1,479
- 7
I just finished breaking the barrel in on my Kimber 6.5/300 WSM Montana. The load seems to show some very good promise that I started with.
65.0 grains of Retumbo over a GM215M primer w/ a 140 grain GK .0125"-.0150" off the lands. I started at the .010" off, which seemed to show a stiff bolt upon opening and I was only in the 2990 fps range @ 20' from the muzzle. So I increased the bullet jump a little at a time, (every three shots). The last three @ .0150" showed no heavy bolt lift, and still produced a 1/2" group w/three shots, the 1st two were right on top of each other. Which was the norm throughout the development, 2-1 out from the other two. Not a lot of speed, but looking at the Hodgdon reloading data online, the 264 WM with the same powder and weight bullet doesn't produce a lot of speed either (3026 fps) and is shown using 1.5 grains less powder!
Funny thing is if you look at the 270 WSM data, and Retumbo with a 150 gr. bullet, the velocity isn't a whole lot faster (3071) and they're using 70.0 grains of powder. And a 160 gr. bullet will still accept up to 68.5 grains of powder at 2989 fps. So I feel like that's about it for the speed/weight/powder combo of this cartridge and barrel length, which is now only 24 1/2" when I had planed on having a 25" tube no real thanks to Shilen Rifles but oh well it wouldn't have made much of a difference any ways.
I now will start with new Winchester 270 WSM brass for the rest of the development, but honestly, with a hunting gun that may only get 600-750 rounds until the barrel is shot out, I may just test the load only another 25 times changing the seating depth and slight powder charge differences. Which would be 50 rounds fired through the gun until I settle with the final tune.
For some reason I can not get the web site to accept a photo! And I have before, it keeps saying its a invalid file name? And makes no difference what I call the jpg photo!
65.0 grains of Retumbo over a GM215M primer w/ a 140 grain GK .0125"-.0150" off the lands. I started at the .010" off, which seemed to show a stiff bolt upon opening and I was only in the 2990 fps range @ 20' from the muzzle. So I increased the bullet jump a little at a time, (every three shots). The last three @ .0150" showed no heavy bolt lift, and still produced a 1/2" group w/three shots, the 1st two were right on top of each other. Which was the norm throughout the development, 2-1 out from the other two. Not a lot of speed, but looking at the Hodgdon reloading data online, the 264 WM with the same powder and weight bullet doesn't produce a lot of speed either (3026 fps) and is shown using 1.5 grains less powder!
Funny thing is if you look at the 270 WSM data, and Retumbo with a 150 gr. bullet, the velocity isn't a whole lot faster (3071) and they're using 70.0 grains of powder. And a 160 gr. bullet will still accept up to 68.5 grains of powder at 2989 fps. So I feel like that's about it for the speed/weight/powder combo of this cartridge and barrel length, which is now only 24 1/2" when I had planed on having a 25" tube no real thanks to Shilen Rifles but oh well it wouldn't have made much of a difference any ways.
I now will start with new Winchester 270 WSM brass for the rest of the development, but honestly, with a hunting gun that may only get 600-750 rounds until the barrel is shot out, I may just test the load only another 25 times changing the seating depth and slight powder charge differences. Which would be 50 rounds fired through the gun until I settle with the final tune.
For some reason I can not get the web site to accept a photo! And I have before, it keeps saying its a invalid file name? And makes no difference what I call the jpg photo!
.
