I have a custom octagon-barreled Ruger #1 chambered for .45-70. I'm considering reaming the chamber deeper to accept .45-90 brass. If I do that, will I still be able to shoot .45-70 ammo if I choose to do so, sort of like .38 Spl. in a .357? I'm thinking of shooting BP and cast bullets with the 90 brass, and still having the option of smokeless and jacketed bullets with the shorter case. Comments? Thanks!
Jerry

Don't even think about it. If you want to shoot BP and cast bullets, the 45-70 will do that just fine. Leave it alone and enjoy it as is. It is a potent and capable piece of kit as is.

If you want a .45-90 To shoot BP I would suggest a Shiloh Sharps or a High Wall. The Ruger in .45-70 will do anything you want to do with smokeless or BP as is

I have never heard of anyone shooting 45-70 in a 45-90 chamber. A .22LR is shorter than a .22 mag but if you have ever seen it tried, you will know why not to do it.
Take a look at this posting.
http://castboolits.gunloads.com/

I have shot a limited number of .38 Spl ammo in a .357 mag but I hate doing so as it really junks up the cylinders. At the time I had the ammo and not a .38 Spl revolver.
I have a Marlin 1894SS in 44 mag and although guys claim you can shoot 44 Spl, I see no reason when you can shoot low end .44 Mag reloads.
Same for a 45-90. I you had a 45-90 and wanted to do so, shoot reduced (45-70) loads. In all honesty, I don't see the need for expense o converting the gun to 45-90 when that Ruger will take 45-70 loads to place where you will regret shooting it, recoil wise.

Yes you can shoot a .45-70 in a .45-90, .45-100 and .45-110 but I wouldn’t advise it. You will ring the chamber and probably have crappy accuracy

You will not ring the chamber. But you are correct about accuracy. The more pertinent question at the moment is, what is the twist rate of a ruger 4570?

Seventy in a 90 is acceptable but not advisable. In a pinch OK, but not as a common practice. If using cast slugs one will likely see a ton of leading with a good bit of shaving occurring at the end of ones chamber. Just run with 90 cartridges and tone them down a bit if recoil is the issue.

The .45-70 smokeless loads I use with 300 grain jacketed bullets are "Slobber-Knockers" according to a friend who fired a few of them and decided he didn't like the recoil. I'm thinking about going to a 250 grain gas checked hard cast bullet, and maybe a case almost full of Trail Boss or some real BP handloads. I can check the twist rate easily enough, but I don't have a clue about it right now. Any suggestions for a moderate-recoil cast bullet recipe? I have plenty of 2-F powder on hand for my .50 caliber flintlock chunk gun if it's suitable for cartridge loads. If there's something better, I'm listening.
Jerry

Jerry, take a step back and ponder need before doing something you’re likely to regret. The .45-70 is fully capable of killing anything in NA and using a wide variety of bullet weights/loads. Making it a -90 will solve nothing and move you further from versatility.

1. Hard cast is of no value re: reduced loads. Softer alloys are the path, especially with BP.
2. DO NOT load light charges of BP for reduced loads unless you fill the void with wad material.
3. 2FG will work fine.
4. Look around at load data, you’ll find a number of recipes that will work. Maybe poke around and find some round balls and go squirrel hunting?

Example from Lyman cast bullet load manual:
293 gr Lyman 457191, 28.5 gr IMR4198 = 1327 FPS.

Same bullet with 12 gr Unique runs 1200 FPS. Both require Dacron wad

Essentially a .44 Mag load, and the list goes on.

The other extreme for your gun could whack an ele....

I guess ring the chamber is the wrong word but it will not do it any good

Never been a fan of downloading anything in my inventory except for youth loads....Having two 45/70's the 45/90 '86 in the pic with the Shiloh 45-110 all are loaded to their full potential..

Each chambering has a slight edge over the other whether smokeless or BP stoked however the 45/90 rebore you're contemplating really isn't necessary IMO..

Keep your present rifle and pick up a '90 for T-Rex protection !

I've done it twice. And while not immediately sorry, a couple years down the road I felt I'd rather I hadn't.

I have and enjoy having a Pedersoli 45--90 Sharps. I go along with leave the Ruger rifle as is., You'll have brass that's easy to find. Plus tons of modern loads. I shoot the 45-90 much more than my 45-70.. Both rifles do well with modest loads of smokeless powder and cast lead bullet, I go along with leaving the rifle be. I got the 45-90 and a 45-110 second hand. Had I ordered them new one or the other would have been a 45-70,

There is no benefit to a .45-90 over the .45-70 if you are using smokeless powder. Black Powder is a different matter

Very true. Even with black, the main advantage of the .45-90 is flexibility in fitting the powder charge, wads, seating the bullet, etc. I've hotrodded a .45-70 with black powder to 1500 yards, but it involved a lot more fussing than a .45-90 would need.

Paul