Chambering and Headspacing a 45-70 Gov't Sharps Rifle

[77 Corvette]

Folks, I'm needing some guidance. I have an old beat up 1874 Sharps Rifle that I've been told is past the point of being a collectible so I'd like to make a shooter from the action and stock. I have a reproduction barrel that is threaded and pretty much ready to go. I've had the barrel dialed in so that up is up at a reasonable torque.

I'd like to be schooled in how they headspaced these old rifles. I was told that the headspacing was done with moving the barrel back until the cartridge met the block. It was crude and that if the block just marked the tooling dye but not the cartridge rim it was head spaced correctly. Is that true? Also on this particular rifle, is the rim counter sunk into the barrel or fit flush after chambering?

I know these are a lot of questions. My deceased Father in Law was a Master Machinist and Gunsmith, and this was a project we never completed. I have access to great machinists, but need some directions specific to these rifles. Experienced Gunsmiths in this area are as rare as blue moons.

Thanks in advance.

[EDG]

>>>I was told that the headspacing was done with moving the barrel back until the cartridge met the block. It was crude and that if the block just marked the tooling dye but not the cartridge rim it was head spaced correctly.<<<

The minimum headspace for a .45-70 is a specific number in the SAAMI standard.
However the brass you use is going to be thinner.
If you set your headspace to a random case it might be too thin for many of the other cases.

I suggest that you either set your barrel up for the SAAMI number. You should be able to make your own headspace gauge.

Or set your barrel up to work with your brass. Measure all your brass and find the thinnest rims and the thickest rims.

1. Set the headspace to fit the thickest rim and all the thin ones will also fit. If you buy a thicker lot of brass in the future the cases will have to be machined.
or
2. Machine all your rims (front face) to the dimension of the thinnest rims and then fit your barrel to use that thin rim value knowing you will always have to machine your rims in the future.

[montana_charlie]

I'd like to be schooled in how they headspaced these old rifles. I was told that the headspacing was done with moving the barrel back until the cartridge met the block.
That sounds right to me ... light contact.


Also on this particular rifle, is the rim counter sunk into the barrel or fit flush after chambering?
Yes, the case head should be flush with the end of the barrel, or only a few thousandths in from flush.

Rim thickness is the determining factor in this, with .070" being the 'nominal' rim recess depth.
Actual rim thickness will typically run .065" to .067", so .067" might be a good choice for recess depth.
Check your brass ...

CM

[77 Corvette]

Thanks for all of the good advice. I think with that I can get close. I plan on ordering enough brass to allow some target practice and then reload, so all of the brass should be of the same manufacture. I'll check the rim thickness and see how that goes.

I do have one question though, if the thickest rim is the target for the recess, then won't I run the risk of blowing the rim off of the thinner ones? I don't plan on letting that happen by staying with the same brand of case.
I appreciate all of your interest.
Steve

[Dale53]

77Corvette;
It would be quite helpful to you to section one piece of brass to see just how thick the solid head and rim are on a modern 45/70 case. If you do this, you will see that there is little danger of having a head space problem that would cause a cartridge head to rupture with this round.
Antique brass is another matter, entirely. Some of those had copper cases that gave serious problems in combat during rapid fire.

If the rifle were mine, I would simply headspace it to SAAMI standards. Modern factory 45/70's are headspaced in that manner and I am not aware of it EVER being a problem. That way, you'll be able to use any modern proper brass in the rifle.

FWIW
Dale53

[77 Corvette]

Thanks again, for the good advice. I'm never going to use anything other than black powder so the pressures shouldn't be great enough to exceed the modern case standards.
I really do appreciate everything you folks have offered. I promise to put it to good use.