Re: 300 WM vs. 300 WSM
Traditionally the WM has had a slight edge over the WSM, especially in the heavier bullets. However, with the introduction of RL17, the 300 WSM "may" now have an edge over the 300 WM. I recently shot 180 E-Tips @ 3193 out of my Sako 24 3/8" barrel with 67.5 gr of RL17 and...... I also shot 210 Bergers @ 2935. These velocites exceed published data for the 300 WM by about 100 fps give or take 50 fps. Having said that, not everyone seems to be getting extraordinary results with RL17, but many do. Also, RL17 may increase WM performance, but probably not to the same degree because it was actually designed for shorter, fatter cases.
If I was to build a 300 WSM, I would use a standard size action and the liberal freebore I currently have in my Sako to allow seating depths that seat the bullet to the lands without encroaching on case capacity. When I seat a 210 Berger to the lands in my Sako, the bearing surface of the bullet only catches about 2/3rds of the neck. If I tried seating a 190 Berger to the lands, it might be falling out of the neck. So in doing your build, whatever you decide, make sure you use an action and chamber the throat for the bullet range you want. On twist... any custom .30 cal barrel I ever order will have a minimum of a 9 twist (and maybe 8) to accomodate the longer high BC custom and wildcat bullets.
Bottom line... If the build is properly designed, and with the right powder and primers, a 300 WSM will come very close to the WM if not actually exceed it, even with the heavier bullets. Assuming the performance of the cartrides is roughly the same, the advantages of the WSM will be longer barrel life and a shorter action compared to the WM. The advantage for the WM is better brass. But you can get Norma brass for the WSM which is great brass if you dont push the pressure limits.
My 30 cal preference... If I were to do a build right now it would be a 300 Dakota which has better performance than the WM or WSM. It also has a fat, somewhat short (not long) case which might be favorable to RL17 performance. it could theorhetically come close to the 300 RUM in performance with significantly less powder. Brass for the 300 Dakota is made by either Hornady or Norma and is not cheap.
Finally, if you really want to shoot to the "longest" ranges and rifle size/weight does not matter then get a 300 RUM or LARGER, fit it with a 9 or 8 twist 30" barrel Sendero contour and you will be killing elk @ 1500 yds or more, especially if some good custom high bc bullets come out. With that size of rifle, recoil should be very tolerable.
Hope this helps and have fun with your project,
Last edited by MontanaRifleman; 07-03-2009 at 04:48 PM.