Bore diameter on Model 1865

[wvmtnman]

I have an 1865, three groove carbine.  The bore diameter is .526.  Was this common?  I thought most were in the .515 range.
        Thanks, Brian

[El Supremo]

Thanks, wvmtnman:

By "bore" are you referring to land or groove OD at breech or muzzle, please?
Smiles,
El Supremo/Kevin Tinny

[wvmtnman]

Diameter from groove to groove.  I ran a slug down the bore.  The measurements were taken from high point (low point in barrel) to high point. 
   Did it two separate times.  Both were .526
 I ask because I was always under the impression that the 1865's were smaller

[El Supremo]

Ok, Wvmtnman:

Three lands and grooves should indicate it is a 56-50.

Measuring the OD's of odd number lands and grooves bore slugs can be tricky. If a 56-50, then a land OD of .500" - .505" and groove OD of .515" - .517" should be within a thou or two.

If you are not skilled, my suggestion is to take the slug to a machine shop or vocational tech school with some doughnuts and coffee in hopes of a graybeard using a triple anvil flute drill micrometer designed for your slug's cross section profile. Those expensive mic's must match the "flutes" so the measurement runs on centers, not corners.   

Measuring across the high spots, grooves,can include extra width when far corner spots are bridged. 

The land OD can be measured close enough by driving a greased, soft 1.5 caliber long pure lead section into the muzzle so that the grooves fill to their corners.  Then carefully tap it out from the opposite end without it dropping onto anything hard, and successively index it and retap so all the high spots are gone. What's left is the land diameter.

A machine shop should have pin gauges in half-thou OD's to feel slip fit, no shake land diameter.   

Don't order a mould until sure of the dim's. 
All the best.
Rl Supremo/Kevin Tinny

[wvmtnman]

A .515 goes down the bore fairly easily and does not fully imprint the rifling.  It's a .526.  I had a gunsmith friend slug it too.
   Someone had mentioned that some early 1865 Spencer's used left over 56-56 barrels.  Didn't know if this was true

[El Supremo]

Thanks, wvmtnman:
A 56-56 bbl on a '65 sorta makes sense.
Guru's here have shared "You can find most anything on a Spencer".
Bbl could be added by surplus dealer. 
Is there a number on bottom of bbl vs frame number?  Tx.
El Supremo/Kevin Tinny