Q: I tried the load you gave me for my 7mm Remington Magnum and it only gave a muzzle velocity of 2860fps, rather than the 3025fps you quoted. I had to increase the charge by 2gn to get 3000fps. Why do you think this happened?
– Trevor George
A: When reloading the 7mm Remington Magnum it pays to stick with the components listed in your manual, if possible.
From past experience I know that case capacity in different brands of brass can vary by up to 10 grains.
I used Norma brass in my old Mauser with 24″ barrel and my two best loads were: Nosler 140gn Partition and 70gn of H4831 for 3284fps; and the 160gn Nosler bullet and 68gn of Norma 205 for 3110fps. The latter was an excellent load.
But then there’s the difference in bore diameters. For your information, some of the barrels I checked in past years varied quite a bit: Remington 700, .2834″; Schultz & Larsen, .2839″; Browning BAR, .2839″; Ruger M77, .2852″; and the Shilen barrel in my custom Mauser, .2844″.
Les Bowman told me he once had five new factory rifles on the shelf at once, all with 24″ barrels, and in the five rifles he found a difference of 250fps with the same loads!
No wonder the data in loading manuals varies so much.