280 vs 270 question

[Tune_up]

I was recently offered a good deal on a .280 so I bought it. Comparing it to my .270 they appear very similar ballistically. But reloading data consistently shows lower maximum pressure for the 280. On Hodgdons web site the powder/loads for a 140 grain bullet show pressures in the range of 49,800-51,000 CUP for the 270, and only 47,000-48,500 CUP for the 280. They are consistently lower comparing same powder loads between cartridges. If case volume and bullet weight are the same (some information shows the case volume of the 280 to be slightly larger and others show the 270 to be the largest, I intend on measuring myself) why would maximum pressures be that different? I am not interested in pushing beyond the maximum loads but I am curious.

 

[rcmodel]

SAAMI max pressure spec for the .280 Remington is 60,000.

It is 65,000 for the .270 Winchester.

The only reason I can think of is the .270 Win first came out in the strong Winchester 54 (later became the Model 70) bolt-action rifle.

The .280 Rem was introduced first in the Remington 740 gas operated Semi-auto.

rc

 

[EOD3]

The 280 was introduced in the Remington pump and auto which are weaker designs. The SAAMI specs are based on the weakest action in use. I wouldn't expect you to see ANY overpressure signs "in a modern bolt gun" until the loads get pretty hot.

OTOH, the 139/154 grain .280/7MM bullet at book velocity will do anything the .270 will do.

 

[Shoney]

About 35-40 years ago, silhouette shooters "discovered" the 280. About that time 7mmMag was the rage, but 280's were consistently besting the "mag".

What they realized was the 280 could produce velocities just slightly under the 7Mag, but with a lot less powder. The thinking was that the more efficient 280 cartridge gave the better accuracy than the overbore 7Mag.

As far as pressure goes, just like in pistol cartridges, if you increase the volume of the case, by seatiing the bullet farther out, the pressure will drop. That is roughly what happens for the 270 - 280 comparrison, bullet weight per bullet weight.