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Thread: Question About Revolver Throats?

  1. #1
    Boolit Master

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    Question About Revolver Throats?

    I spent an hour or so yesterday checking and recording the throats on all my revolvers. I had done this before but over the years had used a variety of measuring techniques. This time I used the plug gauges only. Things pretty much followed what I expected especially the ones that had been worked on or converted by a custom gunsmith. The unexpected thing I ran into was on a couple of S&W revolvers.

    On these some of the throats would only pass a smaller than expected gauge. On a whim, I inserted the plug from the chamber side. On a S&W Mod. 686 the .357 gauge would enter the throat up to the very mouth of the throat. It was almost like a uniform burr existed and about a couple of thousandths material prevented the plug from extending thru. To be clear, 3 throats measured .357 with the plug entering normally from the front. On 2, they would only accept a .356 plug and on 1, a .355 plug. This is the worst example.

    These are guns that I bought used, although apparently shot very little. I would have assumed that with so little material at the mouth, shooting would have burned off a burr(?). Now I'm wondering if I need to have the throats reamed.

    Thoughts? Should I send the cylinders to DougGuy for reaming?
    John
    W.TN

  2. #2
    Boolit Grand Master Outpost75's Avatar
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    On S&W they occasionally faced cylinders after chambering if they only needed to true up and square it a thou or two. This would leave minute burr on the cylinder face. DougGuy can fix.

    When I worked at Ruger all the SP101, GP100 and Redhawk cylinders, frames and parts were CNC and uniform, as were the later 161- prefix Six-series. Parts were fully interchangible so you could grab a random set of parts and assemble a complete gun within Mean Assembly Tolerence without using hammers or files.
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  3. #3
    Boolit Master

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    Thanks! I meant to ask about manufacturing processes that would cause such a condition but left that question out of the post. You have explained it.
    John
    W.TN

  4. #4
    Boolit Mold
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    Most cylinders do not have the same diameter dimension all the way through.
    There is a step 1/8" back from the cylinder throat exit. You can see it.
    You should be able to get larger pin gauges in the rear of the cylinder. Like you saw.

    I prefer cylinders and bullets where I can drop the bullet into the cylinder, but it just barely hangs on that step at the end without going through. This is a great way to measure if you don't have pin gauges.
    That means almost no swaging down of the bullet, but a tight fit.


    Prescut

  5. #5
    Boolit Master

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    Quote Originally Posted by lostindesert View Post
    Most cylinders do not have the same diameter dimension all the way through.
    There is a step 1/8" back from the cylinder throat exit. You can see it.
    You should be able to get larger pin gauges in the rear of the cylinder. Like you saw.

    I prefer cylinders and bullets where I can drop the bullet into the cylinder, but it just barely hangs on that step at the end without going through. This is a great way to measure if you don't have pin gauges.
    That means almost no swaging down of the bullet, but a tight fit.


    Prescut
    The cylinders I mentioned do not have a step(1/8" back). The plug gauge stops just a few thousandths from the mouth. No more than a burr as described by Outpost75. To satisfy my OCD, I'm probably going to send the cylinders to DougGuy for a clean up.
    John
    W.TN

  6. #6
    Boolit Grand Master Outpost75's Avatar
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    Having DougGuy hone to size is the best technical solution to ensure that all six charge holes are uniform and round.

    An expedient used on duty guns back in the day was to also lightly break the wire edge of the ball-end exit using Brownell's ball chamfer cutter:

    Attachment 236488

    Cuts Quick, Duty Gun Chamfer In Cylinders

    Steel cutting tool removes burrs from the outer edge of the forcing cone to improve accuracy. Use on the chamber throat to help rounds drop in easily. Eliminates lead shaving or “spitting” in one or two passes. Unique design works without disassembling the gun. 3/8" tool is ideal for .17 and .22 revolvers. ½" tool works on revolvers from .32 through .45. Revolver Deburring Tool includes cutter and handle. Cutters also sold separately and can be interchanged in the handle.

    080-623-000WB - 1/2" Revolver Deburring Tool - $44.99



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  7. #7
    Boolit Master

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    Thanks! Something to consider. I have some other cylinders that could use the uniforming of all charge holes. It is possible that I could end up with several revolvers with the same throat diameter. The two S&W revolvers are not included in this possible solution.

    I'll have to compare the customs with the standard Ruger Bisley's to see if that is possible. I'm not touching the customs.
    John
    W.TN

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check