There has been a lot of speculation in the difference in velocity between the .280 and 7mm RM on this thread. I already suggested 200 fps with the same bullet weights, which is about what the 4-to-1 formula comes up with, but I got curious--especially after somebody here suggested it was only 100 fps.
So I looked up actual pressure-tested data for the two rounds, on two websites that both use 24-inch barrels, Western Powders and Hodgdon. They also both test a wide variety of powders and bullets. Here are the top velocities for four bullet weights, 140, 150, 160 and 175:
.280 140--2943
7mm 140--3217
274 fps difference
...
Those numbers are amazingly close to my 140g North Fork SS/HP loads in my .280 Rem and 7mm RM. One difference is a 22" barrel for the .280 and 24" for the 7mm.
280 - 140 = 2942fps
7mm-140 = 3214fps
I get 2928fps with a 140 Barnes TTSX. Could probably get more but that load is very accurate (3 into 0.066" last time I checked). I'll take the accuracy. A 140g TTSX in the 7mm can also do better velocity-wise but again I found a good load and am sticking with it.
