Thank you for your reply and actual velocity readings.

From 1985 to 2024 or 2092 fps with a 400 gr bullet.

An old standard seems to be around 2100 fps for the choice DG bullet. So 1985 fps on paper seems a bit slow.

Only using a 400 gr in the 10.75x68 on actual game, buffalo, elephant, would tell the story, if it's a success story or not. At the marginal lower end of the spectrum.

IMO there is no reason not to try or use .404 400 gr bullets in the 10.75x68. if they can becdriven fast enough, stabilised, penetrate well. The bullets originally designed for the 10.75x68 reportedly suffered from too thin jackets. And not penetrating well. .404 Jeffery bullets if driven at adequate speeds should fix that problem. The original .404 Jeffery drove a 400 gr at around 2100 fps and had a good reputation. If the 1985 to 2924 fps or in that range are adequate, it approaches the original .404 Jeffery.

The 400 gr is a heavier bullets than the 10.75x68 was originally designed for. But we have 320 gr 9.3 mm, 350 gr .375, 450 gr .416, .423 bullets made today. All greater in weight than the original offerings. Often with thicker jackets and with a greater sectional density if driven fast enough and stabilised should penetrate very well.

If using a 9,3, .375, .416, .404 (423) on elephant, I'd be tempted to use these 320, 350, 450 grs bullets in a FMJ specification. Particularly in a bolt action. If the heavier bullets hit a target in a usable way similar to lighter bullets, it makes them very versatile. A double rifle of course needs any regulation issues overcome.

I think a 450 gr in w .500/416 at a good speed is possibly more effective, or very similar to a 480 .450/458 bullet. It would have superior sectional density and penetration at a comparable speed. For a slightly lesser calibre frontal width. Again of course regulation issues aside. I would not have a .500/416 built and permanently regulated for a 450 gr, rather a usual 400 gr.

Back to the 10.75x68. Most certainly a vintage classic suitable for large soft skinned beasts. Which might proven a buffalo and DG cartridge at the lower range with modern powders and bullets.