RN, Back in the sixties I used to be cash negative on a regular basis. I couldn't afford to purchase several different powders and bullets. Not only that, most stores just didn't stock them and order times were ridiculous as far as turnaround times went anything from 6 weeks to 6 months were common. This wasn't just with hand loading components but everything from food to clothing to parts for vehicles.
This was about the time I started casting my own bullets. Lead was all over the place and could usually be picked up free just to get rid of it. I went through the normal learning curves and Lyman manuals, along with a few rather long in tooth mentors whom I wish were still around, to aide my plodding ways. There was a lot of information around concerning casting lead bullets and applying gas checks or even making them out of old soda cans. Please bear with me on this, I will get to a what worked for me answer quickly.
Your question is not easily answered because you don't indicate which bullets you will be using. Also, which 25-20 cartridge you will be using.
30 caliber and 31 caliber bullets were relatively common but only in weights from 150 - 220 grain. Flat nose were often not available but round nose bullets were fine in the lever action tubular mags. I was told all sorts of horror stories about mags Kabooming but never witnessed it with round nose bullets. Some old military rounds were loaded into tubular mags with round nose bullets with few or no adverse effects.
OK, back to casting. As mentioned lead was readily available. I picked up just over a ton of it from the local dump. I had an old 51 Chev half ton and it took me 4 trips to get it home. When I first found the lead there was appx 500 -600 pounds and it was all covered with roofing tar and had nails all through it. By the time I took it all home over a 4 day period, dead of winter, after school, the pile had grown to over a ton because the contractor very nicely put the rest of it from the project he was working on (school roof) onto the pile when he realized someone had a use for it. None of the metal recyclers wanted anything to do with it. People were recovering their roofs with Asphalt with aluminum or corrugated iron flashing. Lead was seen to be an abomination. Some people had even used lead sheathing on the outside of their walls to deter termites etc. Most of that lead is in land fills because it wasn't worth recovering for salvage.
My big problem was that all of this lead, once the tar was melted off and the nails floated out, was pure and soft as butter. I was allowed to melt this stuff down by one of the local sawmill managers in their Beehive burner. He was one of my mentors. Nice Guy. He had a bunch of Babbit they used for casting Pillow Block bearings and making repairs to bushings. Industrial Babbit used for such applications is about 90% Tin with the rest being made up of Antimony and Copper. Some also had Zinc in the mix but those were for specialized purposes. Some nations such as Portugal and Spain used Zinc in their cast bullets.
OK, I think you get the idea. Cast your own bullets for all of them. Order a .311041 mold from Lyman, with a set of handles of course, get a cast iron pot from the 2nd hand store etc and do some due diligence. Use the bullets as cast directly from the mold for the 303Brit and if you feel it necessary (it isn't) for the 30-30, run them through a sizing/lube die. Lead and Tin are still available in lots of forms and this has been discussed to death on other threads.
Now for powder. I used to use one powder for cast lead loads and a different one for jacketed loads. Both of them worked for the three cartridges you mention with both published loads and some experimentation.
Those powders were and still are IMR3031 and IMR4198. These to powders will work well with jacketed bullets and with cast bullets, with or without gas checks. I do like gas checks and would highly recommend their use but at low pressures and velocities they may or may not work better for accuracy.
I have used these components together for over 50 years to present day and they still do the job well. I still use the same 30cal and 25cal single cavity molds/handles I purchased in the mid sixties along with the same melting pot and pouring ladle. There are all sorts of ways to make good bullet lubes and gas checks if you have that valuable commodity, time, to spare. You could even look into swaging your own jacketed bullets. It's one hell of a learning curve but if you're into it, lots of fun and chock full of information that can be used in other hobbies and even work place applications.
That's the beginning
