I would recommend that you buy a box of Federal Premium Gold Medal Ammunition with the 190 grain Sierra Match King bullets , or the Federal Premium Gold Medal Ammunition with the 215 grain Berger Hybrid bullets to shoot through your .300 Win. Mag rifle . Both of these should shoot very accurately , and have very consistent velocity spreads . The overall length of the cartridge with the Berger bullets is listed as 3.6" which might be too long for your magazine .
If you can find either of these , they will be expensive , over $70.00 per box of 20 , but either will be your best chance of getting accurate ammo , that has not been custom developed for your specific rifle .
I have no idea of the cost of the ammo that you are having loaded for your rifle , and that is none of my business , but these 2 Federal cartridges would give you an idea of your rifle's potential , as well as establishing a baseline of costs involved in your pursuit of having your current company develop your loads .
DMP25-06