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Optimal 1851 Navy Throat Measurements?

Discussion in 'Blackpowder' started by Mossyrock, Nov 28, 2010.

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  1. Mossyrock

    Mossyrock Member

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    Gents,

    I have two 1851 Navy revolvers. One is a recent-production Uberti, and the other is a Second Generation Colt. While the fit and finish on the Colt are superior to the Uberti (and should be), the Uberti is considerably more accurate. That being said, the cylinder throats on the Colt measure as follows:

    1. .372"
    2. .373"
    3. .3725"
    4. .3725"
    5. .373"
    6. .373"

    The Uberti measure a VERY consistent .3755". Based on this, it looks like I need to recut the throats of the Colt to .375". Any idea where I might be able to come up with a .375" throat reamer?
     
  2. Old Fuff

    Old Fuff Member

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    Before you ream anything, slug the bore of each revolver. The chamber throats shoould be about .002" over the bore grove diameter.

    For a reamer, try: www.brownells.com and www.dixiegunworks.com

    Also remember that if you increase chamber diameter you must also use larger balls or bullets, so be sure you have a source for them.
     
  3. mykeal

    mykeal Member

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    +1

    Don't touch the chambers until you know the bore groove diameter.
     
  4. Mossyrock

    Mossyrock Member

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    That sounds like a grand plan...right up to the point you try to measure a bore diameter with an odd number (seven in this case) of lands and grooves. Measuring across the center of the slug (covering one land and one groove), I get .3712". Suggestions?
     
  5. Old Fuff

    Old Fuff Member

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    On your slug, the land = groove diameter in the barrel, where the groove = bore diameter. According to Uberti specifications the grooves in the barrel should be .010" deep, with bore diameter being .360" and groove diameter being .380" If you are measuring groove-to-land I would expect that in your barrel the bore diameter is .371", less (one) rifling depth (or about .361").

    If you can, use a depth caliper and measure from the top of a land to the bottom a groove to get groove depth (rifling depth), then add that to .371". If all of this is correct, total groove diameter should be .281".
     
  6. rcflint

    rcflint Member

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    According to the Cimarron list of Uberti dimensions, the 36 bore is .360 (9.144mm) and the groove .379. Since the metric dimension they give for the grooves is very incorrect, (9.16) it might cast doubt on the groove depth figure, though reversing the 9.16 to 9.61 gives you .378.

    If the Colt shoots accurately with a .375 chamber, and a .375 reamer is a standard size, I'd go for it. Try Enco for chucking reamers.
     
  7. J-Bar

    J-Bar Member

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    After opening your chambers, if a .375 ball is too loose, try a .380 ball or even a 0000 buckshot, which measures about .382. Lee make a .380 round ball mold, and my 1851s love them. You can buy 0000 buck in bulk from Ballistic Products. It's not pure lead, but if your chambers are opened up some, you can still seat them without too much effort.
     
    Last edited: Nov 28, 2010
  8. Mossyrock

    Mossyrock Member

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    +1 on the .380 Lee mold. I am on my second...I wore out the first. It's the only round ball I use with my Navy revolvers.
     
  9. iron horse morgan

    iron horse morgan Member

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    One method to measure a bore slug with an odd number of grooves :

    -Wrap a piece of brass shim stock around the slug. I suppose a beer can will work fine too, or whatever else you have that is flexible enough to wrap firmly, one time, around the slug.

    -While pinching the shim stock with the fingers of one hand, measure the O.D. of the wrapped slug with a micrometer.

    -Subtract 2X the thickness of the shim stock from your measured O.D. to obtain the correct diameter of the slug. For example, if your chosen shim stock is .004 thick, subtract .008 from your measured O.D.

    As the others have suggested, slug the bore before reaming the chambers.

    Hope this helps.

    Iron Horse Morgan
     
  10. mykeal

    mykeal Member

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    To measure the lands and grooves in a barrel with an odd number of lands, first measure the cross section diameter of the bore land-to-groove; this is preferably done using a lead slug that has been swaged into the bore. Drive the slug in from the muzzle end down to a depth of at least one and one-half ball diameters, then push it back out the muzzle end. If the barrel has a closed breech the use of Cerrosafe is recommended.

    Once the land-to-groove dimension is determined, use a caliper to measure the thickness of the barrel wall at the edge of a groove. If the barrel is round any groove will suffice, but if it's octagonal the measurement should be done using a groove that is as close to the center of a flat as possible. Next, measure the barrel wall thickness the edge of the land next to the location where the groove wall thickness was measured. These two measurement must be taken as close to each other as possible. Subtracting the two measurements gives the groove depth. This method is not exact, and three or more samples should be obtained at different locations if possible and averaged together.

    Once the groove depth is determined, subtract it from the land-to-groove dimension off the slug to obtain the land diameter and add it to the land-to-groove dimension to obtain the groove diameter.
     
  11. scrat

    scrat Member

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    IFFFFF you need to or want to get the cylinders all the same size i would recomend honing first. Get a 2 stone wheel cylinder hone. then hone out the insides of the smaller ones to get them to the same size as the others. I would not recomend any other method. Other than taking it to a machine shop or a gunsmith with machine capabilites so that the cylinder can be properly done.
     
  12. whosyrdaddy

    whosyrdaddy Member

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    The easiest way I have found is to slug the bore by driving a lubricated ball through the forcing cone and halfway down the barrel and compress it between two dowels until it completely fills the grooves.

    Then using a 5A adjustable reamer, 21kzRzUzv9L._SL500_AA300_.jpg found here
    carefully ream the chambers just until the slug drops in freely. Finally, measure for the appropriate mold.
     
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