E - been loading my 280 since before they were fashionable, 1982 to be exact. Coincidently bought my first 7mm mag the same year in the same rifle. You are absolutley correct on your assessment of the 280 vs. 7mm mag statements.
The 280 rem case (at least mine) holds 70.0 grains of water, my 7mm mag case holds 85.0 grains of water. Simple physics - Ideal Gas Law (PV=nRT) - implies the physical impossibility of the two being equal, regardless of the mystical powder stuffed into each respective case. Greater volume equates to a larger volume of gas and stored energy in the case. It is the expansion of the gas produced by igniting the powder that causes the bullet to accelerate down the barrel. In simple terms: More volume (V) = more powder = more velocity - assuming identical pressure. There are no magic powders, cartridges, guns, barrels, etc to make up for a signficant decrease in case capacity - loaded at the same pressure. Obviously, if you are achieving higher than stated velocity with a significantly smaller case, you are running at higher pressure. Period.
From a personal standpoint, I've hot-rodded my 280 into a baby 7 Mag, stuck bolts, blown primers and never reached factory 7Mag velocities. To keep all things in perspective, here is load data from the Remington website for the 7Mag:
140 - 3175 ft/sec
150 - 3110 ft/sec
160 - 2950 ft/sec
175 - 2860 ft/sec
Here is pressure tested 280 loads from the Hodgon website for the 280 Rem
140 - 3010 ft/sec @ 51,000 CUP
150 - 2990 ft/sec @ 51,600 CUP
154 - 2880 ft/sec @51,600 CUP
175 - 2650 ft/sec @ 52,000 CUP
Using a pressure standard, the loads are not close, nor are they capable of being close at the same pressure. Frankly, I thought the 280 SAAMI pressure was 50,000 CUP not the 270 Win standard of 52,000. Maybe it's the 7mm Express moniker that allows higher pressure. As a side note, the 280 Rem loads listed above are likely at higher pressure than the listed 7 Mag factory pressures due to the 7 Mag tendency of pressure spikes, which necesitated decreasing the factory pressure levels a bit.
Barnes and/or Nosler load data may show higher 280 velocities than those listed above, but I've never been able to attain them in my guns, nor any other I've loaded for.
Bottom line: each of us chooses how close we go to the "line" or beyond. A hundred feet per sec ain't worth my life. I may be paranoid but I watched my dad blow up a 06 Husqavarna at the age of 8 from ~ 6 feet away. It's a good thing he shot it from the hip because we never found all the pieces - your face ain't much of a backstop...........
-- BW
