Got a Question.

[Jack]

Probably you know as much as I do, Skeet.
Rocky Gibbs was a gunsmith in the same era as P.O.Ackley. Gibbs developed a line of ultra 'improved' cartridges- meaning the parent cartridge is blown out about as much as the brass can stand. Gibbs cartridges will NOT chamber in a factory chamber- the shoulder has been moved forward on all the Gibbs line.
The parent case for the 25 Gibbs is the 25-06 or 30-06, I believe.
Rocky Gibbs may have worked with belted cases, too, but his line of super improved cartridges is what he's known for.
Loading data? Good luck. I think you could start with 25-06 improved data, and work up from there.