for practice, I took some X-Treme 7.62 plated bullets(which I've used before for other things) and gave something a try. Some rifles with .308 bores you can use them in as-is; others they don't work; in this case a .300 Blackout would not fully chamber them*. So could you size them?
Yes. Yes, you can. I lubed some and ran them through a Lee .308" sizer die, and checked them after; by my caliper all very consistently .308" diameter, and no sign of the plating tearing or otherwise doing something nasty.
That left load data. X-Treme recommends a max velocity on these of 1500fps(We recommend keeping velocities to less than 1500 FPS (Feet Per Second) and using only a light taper crimp). In the 7.62x39 I found the light load I worked up was running them ~1800fps, way over what X-Treme recommends, but with quite good accuracy out to 100 yards and no nastiness left behind in the bore. The Nosler load data showed the lowest velocity with 125-grain bullets with 2400 propellant, 1764fps with the lowest charge, so started with that.
It works. Pressure's low enough the gas block had to be opened one click to reliably cycle the bolt all the way, otherwise no problems: fed, fired, and decent accuracy**, good enough for general practice at short ranges. And bullets a lot less expensive than standard jacketed. I did have a chance to run some over a chronograph, and they averaged 1627fps, more than 100fps slower than the manual indicated, and considering these are much softer than a standard jacketed, slower than expected.
Yes, I am aware X-Treme makes a 150-grain in .308; if I can pick up a few I'll try them. They may not work in the rifle in question due to their shape/length.
Lots of room to experiment with this. Change the charge/propellant, if I can borrow a .309" die try them at that diameter, etc.
*yes, tried different seating depths, no good. So sized one, loaded a dummy, and tried it, and since it worked went from there.
**This was tried in a rifle that only had a red-dot with a slightly blurry dot, so 'decent' means about 1.5" groups at 30 yards. With a better optic/shooter that might shrink a bit.