[MinervaDoe]

I was looking at my Lyman manual, and I noticed that the difference in velocities for the 110 grain bullet is only about 100 fps.

I also noticed that the manual uses different powders for each cartridge.

How do these cartridges compare ballistically?

I've heard the 6.8 SPC is touted as a good cartridge for a short barrel rifle, that can reach out to 600 yards. But, would both cartridges be roughly equivalent in a Mini-14?

Is the 6.8 getting its extra 100 fps by using fast burning modern powders?

[steve4102]

But, would both cartridges be roughly equivalent in a Mini-14?

The Ruger Mini-6.8 is cut with a SAAMI spec reamer. The rest of the world has scrapped the SAAMI chamber and adopted the 6.8 SPC Spec II chamber. The spec II has the proper throat dimensions allowing the 6.8 to run safely at it's designed 58K psi.
Load data for the 6.8 with a 20 inch barrel runs a 110gr bullet at about 2600fps @58K psi. Load data for the 7.62x39 with an 18 inch barrel runs a 110gr bullet at 2675fps or about 2720fps with a 20 inch barrel.

Is the 6.8 getting its extra 100 fps by using fast burning modern powders?

Mosley because it runs at a higher pressure than the x39.

[MinervaDoe]

That's very informative. A little Internet searching finds this.
6.8 SPC Chamber Drawings
http://www.frfrogspad.com/68chambers.htm
and this:
The 6.8 SPC (6.8 x 43 mm) Cartridge
http://www.frfrogspad.com/68spc.htm

6.8 SPC SAAMI specs call for a max average pressure of 55 k psi
6.8 SPC military loading runs around 58 k psi
It delivers greater energy at all ranges than either the 5.56 or 7.62 x 39 rounds.

7.62x39 = 45,000 psi

The tables in this article saved me a lot of reserch time.
Thanks for pointing me in the right direction.

Using the "DMR" chamber, a 1:11 twist 5R rifled barrel, and specially designed high velocity 80 gr copper bullets (part number 270080HV063)from GS Custom Bullets in South Africa (www.gsgroup.co.za) velocities close to 3400 f/s have been achieved, and with an 85 gr Barnes TSX copper bullet velocities close to 3200 f/s have been achieved from 16" barrels