I'd guess that if you over load the .280 as much as you over load the 7x57 you'll gain about 100-150 fps more same as the .30-06 over the .308. You do realize don't you that you are claiming within 200 fps of 7 Rem. Mag velocity for a 100 year old warhorse round with perhaps two thirds the case capacity of the magnum?
From the Hornady Manual there should be closer to 400-450 fps difference. The excessive pressures you are developing are accounting for the rest. The .280 with max loads is actualy supposed to be able to barely reach 3000 with a 140.
Old topic but worth reviving.
I've been reloading rifle ammo for over 35 years now, and the OP most likely had a very good point, before he deleted his posts. If you firmly believe something and have done the research and R&D, there's no shame in having faith in those findings.
Example: It's common knowledge with aftermarket bullet and powder mfrs. that the 8x57 can be loaded to approximate 30-06 pressures and velocities, provided the 8x57 is in a 1905 or later model 98 Mauser action, or commercial Winchester, Remington, Ruger, Savage, etc. bolt action with dual locking lugs and a safety lug, and modern steels, i.e. similar to the Mauser.
Logic dictates the same holds true for the 7x57 and the 280, both having the same type of cases as the 8x57 and 30-06, and share the same sibling relationship. The reason the 7x57 is always "loaded down" by ammo mfrs., and the load data on the soft side, is there's a lot of old pre-model 98 antique weapons still being traded and sold and used, that cannot safely take the pressure levels of a full-on 7x57 load. I had quite a few of them, and looking over the bolt of a M91 or M93 Mauser without a safety lug, can be an uneasy feeling. Not something I'd want to load up hot. So the loads best be on the safe side, i.e., on the low pressure side. Shooters do get hit in the face with broken bolts from time to time, and it's no doubt a horrific experience, and deforms their face for life- if they survive it.
But, having said that, if one already owns a strong M98 action, the 7x57 can "judiciously" be loaded using 280 Remington load info. Think about it. You can rechamber any M98 large ring action, for 280 Remington, so why would it not handle a full on 7x57 load using identical load data ??
Example 2:
Now look at the load specs for a 145 grain bullet. I have an old Speer reloading manual that lists 7x57, 54 grains of 4831, at 2890 fps, as the "hottest" load.
The next page lists the 280 Remington, 58 grains of 4831, at 3000 fps as the "low" load, and 62 grains of 4831 at 3180 fps, as the "hottest" load, same bullet.
I have no doubt an M98 Mauser in good condition, would live just fine with 58 grains of 4831, behind the 145 grain bullet, approximating the 3000 fps 280 Remington starting load- providing the 58 grains of powder fit in the 7x57 case. I would not compress the charge.
Anything the 7x57 can do, the 280 will do a little better, especially with a heavier bullet, which is usually the situation with 2 similar cartridges of same caliber and case head design, but different lengths. Where the smaller case has an advantage, is lighter bullets with very fast powder, not leaving as much empty air space in the case, as the larger longer case would have more empty space, as the powder got faster.
The natural progression and trend from the late-1800's onward, has been reduce case capacity, and increase powder burn rate, to get the same velocity as the old longer case used to get, by using less of a faster powder. The end result is just as much power from a smaller cartridge length.
Example 3:
The old 1980 Hornady reloading manual got to the heart of the matter, it had this listed in the 8x57 section: "The loading data presented here is for use in Model 98 Mauser actions or any other modern action chambered for the round. Do not use this data in the Model 1888. Reduce all loads by 25% and work up loads very carefully"
So let's look at the load data in that manual, comparing 7x57, 280 Remington, and 8x57 from Hornady, these are max loads:
7x57 4320 powder, 154 grain bullet, 44.8 grains powder, 2700 fps
280 Remington, same bullet, same powder, 47.7 grains powder, 2700 fps
8x57, same powder, 150 grain bullet, 53.5 grains, 2900 fps
A few interesting things are evident: Why would the 8x57 with nearly same case, with similar bullet weight, list nearly 10 grains more powder for the max load, over the 7x57 ? The larger circumference bullet of the 8x57 has even more friction and would create more pressure.
and even more interesting, why would the 8x57, a shorter case, be listed with 6 more grains of powder, than a similar weight bullet in the 280 Remington load, and more velocity ?
finally, notice how the 280 and 7x57 loads have the same velocity, even though the 280 is burning nearly 3 more grains of powder ?
it's the law of diminishing returns kicking in, i.e. the longer the case, much more powder must be burned, to gain only a tiny bit more velocity, if the bullet weights and powder burn rate are the same. The only way to really kick velocity up higher, is use a LOT more powder, or go to a faster burn rate powder.
Obviously the bullet and powder mfrs. are covering themselves legally, by listing the 7x57 with much lower pressure loads, with old guns chambered in 7x57 in mind. The 7x57 cartridge is nearly the same age as the 8x57, the same case length, yet look at the difference in load pressures and powder charges and velocities. In other words, if they "load down" a 7x57, why aren't they "loading down" the 8x57 too. Reason- most 8x57 guns are M98 actions or better, they are very strong, and can take the pressure. And they list a "caveat" warning in the load data. (but FWIW, I did have a M93 Turk that was German made, and rechambered for 8x57, so one must always be judicious and on guard).
If you are using a modern rifle or good strong Mauser M98 action, the 7x57 can be "judiciously" loaded to approximate 280 Remington velocities, just like the 8x57 can approximate the 30-06 to a large degree. The key operative word is "judiciously" - do the homework and proceed with caution, relying on safety and common sense.
