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Thread: Bullet 'bump up' in revolver throats

  1. #1
    Boolit Master newton's Avatar
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    Bullet 'bump up' in revolver throats

    Typically we want the throats of revolvers to be a couple thous over groove diameter correct? I have been reading and seeing that some have tested what happens by shooting some loads without a barrel screwed on(I think they were using Dan Wessons). They found that the bullet, sure enough, bumped up to fit the throat.

    So, my question is how this affects loads if you choose to shoot jacketed ammo. Do the jacketed bullets also bump up? I would think they would given the amount of pressure behind them. I know they are not as soft as lead, but they are not as hard as steel either.

    If they do bump up, say we are talking about 44 magnum that had its throats opened up/evened out to .432", then is it bad for that jacketed bullet then to be shoved through the forcing cone and squeezed down to .429" by the barrel?

    I have to think that it's not really an issue because I do know that a lot of guys who shoot cast also shoot some jacketed bullets from time to time. It just made me wonder about it all when I was reading and started thinking about it.

  2. #2
    Boolit Master
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    I have to think that it's not really an issue
    This ^^^

  3. #3
    Boolit Master newton's Avatar
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    Well, maybe I didn't really pose the question in the best way.

    I know that we all probably choose cast boolits over jacketed ones to shoot most days. I have to say I do for an honest 90% of the shooting I do, if not more. So thinking about things that have to do with j-bullets most likely is put out of mind for most.

    What got me to thinking about it is the gun I have. It has right around, or just under more likely, .432" throats - probably closer to .4315". I found some relatively 'cheap' j-bullets that I got just to play around with. They measure .431", and are a very nice snug fit in the throats of the cylinder. I thought this was a pretty great thing really.

    Then I start looking around at what others might be using for loads and much to my surprise I started seeing a lot of concern(on other non-cast boolits sites) about shooting a j-bullet that is so much over groove diameter. Kind of like shooting a .310" bullet in a .308" bore. Myself, I did not see a concern so much as I know that if I were to take that j-bullet and run it through a Lee sizing die at .429", it might be kind of tight, but I bet I could push it on through. So, I am sure the force required to push the oversized j-bullet through the forcing cone is easily accomplished with the pressure that the load generates.

    However, my thought is more toward wear and tear on the forcing cone - probably not an issue - but more so toward accuracy and such with the j-bullet. How much deformation takes place? With cast boolits, I think that the lead takes the transition better. I am curious how copper takes that kind of transition though.

    So that's the background of the question. I wonder if a j-bullet bumps up in a cylinder throat like a lead boolit does, and if it does, how does it affect things?

    I know, I know, I am "overthinking" it. Not really, because I think its good to consider these things when doing work on guns. How much over groove diameter does a revolver cylinder need to be? I know this is a "cast boolit" website, but I still think that people here also shoot j-bullets from time to time. I wonder if the ideal size of a cylinder throat would'nt just be .001" or so. I realize we deal with the hand dealt us in these regards. I feel lucky to have the throat diameter I do with the groove diameter it is. But, if I were to get a revolver with super tight throats I think I just might only have them opened up to .001" over groove. I have heard of some S&W throats being under or right at groove size.

  4. #4
    Boolit Master

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    J words generally have a pure lead core and given there is enough pressure, they will EASILY obturate to the throats when fired.

    I still maintain my recommendations of boolit .001" to .002" over groove diameter, throats .0005" to .001" over boolit diameter. This just works in every caliber I know, for cast or j words.
    Last edited by DougGuy; 03-02-2018 at 10:27 AM.
    Got a .22 .30 .32 .357 .38 .40 .41 .44 .45 .480 or .500 S&W cylinder that needs throat reaming? 9mm, 10mm/40S&W, 45 ACP pistol barrel that won't "plunk" your handloads? Shoot me a PM! Also on Facebook: https://www.facebook.com/Cylinderhone-756429174391912/

  5. #5
    Boolit Master



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    DougGuy: I have a question

    ? If barrel groove and cylinder throats muster up to the specks you like. what harm or bad things can be seen shooting bullets with a hardness of say 16, at lower Vel. Say around 1000 F P S

    Seems bumping up would not be an issue.
    Could you please comment on this.

    Thank you
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  6. #6
    Boolit Bub PhantomRider64's Avatar
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    Lurking,,,

    My SAA clone has groove dia .452 and throat dia .453.

    Sent from my SM-S920L using Tapatalk
    Short,Fat,and Slow,,,Yup I love the .45

  7. #7
    Boolit Master
    9.3X62AL's Avatar
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    Quote Originally Posted by PhantomRider64 View Post
    Lurking,,,

    My SAA clone has groove dia .452 and throat dia .453.

    Sent from my SM-S920L using Tapatalk
    This is the finished spec for my Ruger Bisley Blackhawk. I shoot bullets at .454" sizing, and I get good to excellent accuracy with every design from 200 to 310 grains. 85%-90% of my shooting gets done with Lyman #454424, 10.0 grains of Unique for about 1000-1025 FPS. Probably a little warmish for Colt/Uberti SAAs, but a day at the beach for the Rugers.
    I don't paint bullets. I like Black Rifle Coffee. Sacred cows are always fair game. California is to the United States what Syria is to Russia and North Korea is to China/South Korea/Japan--a Hermit Kingdom detached from the real world and led by delusional maniacs, an economic and social basket case sustained by "foreign" aid so as to not lose military bases.

  8. #8
    Boolit Master



    curator's Avatar
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    While some jacketed bullets will "bump-up" to throat diameter in revolvers, how much depends on the hardness of the jacket and the chamber pressure of the cartridge. J-bullets have an inherent advantage over cast boolits in that their hardness will allow them to 'self-center" in the rifling even if slightly under size. Additionally, copper alloys are not any where as susceptible as lead alloys are to hot gas erosion if powder gas does leak past then in the rifling's grooves.

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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
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LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check