Accuracy of 56-50 cartridge in 56-56 rifle

[El Supremo]

Hello:

Yesterday, the owner of an unaltered, original four-digit 56-56 1860 Spencer rifle, test shot it alongside me using smaller bullet, 56-50 rounds to learn relatve accuracy with the looser diameter bullet.

The 56-56's barrel has six lands and grooves, with its lands approx 2.4X wider than the narrower grooves.  Carefully measured twist is (repeatedly) 48".  Muzzle LAND OD is .540" and GROOVE OD is .554" for rifling depth at the muzzle of .007". A replacement center fire upper block was installed.
Trigger pull is around 8#, with a slight hitch.

The 56-50 rounds used old S&S, standard dim, salt bath annealed cases. The case OAL was 1.600", with 35gr 3Fg (US) Swiss, ACCURATE #51-320S .511" sized bullet in 30:1 alloy with SPG lube. Light crimp and loaded round OAL of 1.57".  These rounds cycled easily from the tube magazine.

Using a front bag rest at roughly 43 yards, and a 24" wide X 30" high cardboard target with 6" bull and the original, challenging issue sights:

All rounds fired and extracted easily with no splits.
The first shot from clean dry bore key-holed 90-degrees about 10" at 1:00 from bull center. Second shot 4" right of first shot half as key-holed. Next ten shots produced a 24" C-T-C  , scattered group surrounding the bull with either zero or barely yawed holes.

A 56-56 round was fired with a case full of 3F Swiss, which hit squarely in the aiming bull. 

The first lightly water wet patch pushed from chamber out the muzzle with coated flex rod had leading in the heavy fouling.

Our conclusion is that shooting the smaller diameter bullet 56-50 round in an issue 56-56 rifle might be combat accurate to 50 yards, with worse than "smoothbore" accuracy. At least we have some info vs conjecture.

Smiles,
El Supremo/Kevin Tinny

[Coal Creek Griff]

That's very interesting. Thanks for the report on your tests!

Griff

[Allletters]

Just picked up my first Spencer, an 1860 model in .56-56. Good to know what to expect from a .56-50, I had heard they would function in the larger bore gun but never heard any details.

[Sedalia Dave]

They'll function, but barrel leading will be very bad.

The effort required to remove the lead from the barrel is not worth it in my opinion

[mgmradio]

 56-56 ammo can be shot through a 56-50 with no real problems with accuracy, but as you have found the opposite doesn't work well.

[Trailrider]

Originally, both Spencer-made M1860 Carbines in .56-56 and Burnside-made carbines in .56-50 were in use in various cavalry units, especially various companies of the 7th Cavalry. Logistically, it is likely that either ammo was available and issued to the troops. The 3rd Infantry was the only infantry unit west of the Mississippi that was issued M1860 Spencer rifles, also .56-56 (actually known as the #56 cartridge). Keep in mind that Spencer carbines were not intended to produce as good accuracy as the infantry rifle-muskets, in .50-70. The Spencers were, you should excuse the expression, the "a$$xxlt weapons" of the day.

Given the differences in manufacturing dimensions of modern reproductions and ammunition, you can probably get acceptable accuracy using .56-50 ammo in the barrel of an original M1860 carbine in .56-56. The actual rifling of the original M1860 carbines tapers from breech to muzzle (.545 down to .535" by actual measurement). With soft bullets and black powder, it should be okay.