Re: .270 Gibbs
I have a 340 Gibbs. I make brass out of 35 Whelen. You should do fine to make your brass from 280 Rem. or 30-06. Adjust your die so that it necks down your brass just far enough to create a false shoulder. There should be a bit of resistance when you close the bolt on your rifle. Some then take a bullet and load it long into the lands and fireform with a light load. I've loaded mine with 20 gr. of Red dot and filled the rest of the case with cream of wheat, with some white glue on top to keep it all from spilling out. This has worked well for me, but the odd case doesn't fill out the way it should. You CANNOT simply fire a 270 Win in your chamber like in an Ackley improved version. There just isn't anything to headspace off of.
I ordered my dies from RCBS. They were expensive and it took awhile to get them. Good luck, Eric