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Thread: Sizing bullets to cylinder throats

  1. #1
    Boolit Master curioushooter's Avatar
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    Sizing bullets to cylinder throats

    I never really paid much attention to this sort of thing until recently...when I read an article in Handloader that reccomedned sizing bullets to match revolver cylinder throats. Makes sense to me.

    I pin gauged my S&W 624 (44 special) and all six throats will take a .432 pin but not a .433.

    Is there rule for what bullet sizing die should be used? A .432? I suppose I should want a mold that throws at least a .432, too.

    There is a very slight barrel constriction at the threads. Is there a way to lap this out without further enlarging the throats via fire lapping (which I've done to other firearms besides revolvers)?

  2. #2
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    I haven't read that particular article, but that is the general consensus. I started sizing to throat size as soon as I started casting handgun bullets as I had read so many threads stating that if you wanted accuracy and clean barrels you should (more or less). To me it made sense and it has been the case for me. Another good point you read is having the throats being as close to the same as another accuracy "trick" and it too has been the case for me.

    Sometimes this bullet sizing gig can be a chore due to having very large throats. You can always size smaller, but you can't size bullets larger is a fact though🤣🤣🤣.

    Your barrel constriction issue has been covered many many times. A blued barrel is easier to fire lap than a stainless barrel is also a general consensus. The Rugers seem to be more likely to have this than a Smith, or at least I pay more attention to single actions than double actions so I've read more about the issue there. I've been lucky with barrel constrictions and not so lucky with mismatched undersized throats.

  3. #3
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    What happens to your theory when you have a throat larger than your barrel? I guess I'll continue to size bullets to the barrel.

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    Boolit Master
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    If the throats are not larger than the barrel, you can send the cylinder to DougGuy and he will fix it.

  5. #5
    Boolit Master
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    Quote Originally Posted by 6bg6ga View Post
    What happens to your theory when you have a throat larger than your barrel?
    You still size your bullets to the cylinder's throat size. I have a couple of the early S&W Model 25's with the large throats and size my bullets to .455" even though the barrel is .451" - .452".

    Don
    NRA Certified Metallic Cartridge Reloading Instructor

  6. #6
    Boolit Master

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    Size to throats and let the forcing cone sage the bullet down. If it is a blued gun, fire lapping with easily remove the barrel thread choke constriction if it is minor. Check Bear tooth Bullets website for details.

  7. #7
    Boolit Master curioushooter's Avatar
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    What happens to your theory when you have a throat larger than your barrel? I guess I'll continue to size bullets to the barrel.
    You better hope your throats are larger than the groove diameter of the barrel. If they are not they swage the bullet down and it is undersized for the rest of the trip down the barrel.

    With softcast bullets and most thin jacketed bullet in theory they obturate to fill the bore if there is adequate pressure. There are of course limits.

    I've read every thread on this forum regarding lapping constrictions. I didn't find an answer to this, at least what I consider a satisfactory one: I have heard of folks putting abrasive in the barrel and then firing the projectile so that the throats never see the abrasive. Anybody work this out? I am not enlarging already larger throats or making them potentially different. Also, they are perfectly mirror glass shiny smooth. Any reputable folks out there that perform hand lapping?

  8. #8
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    "My" rule of thumb has been to take a sized, lubed, bullet, and drop it into a cylinder. If the bullet falls through by its own weight, or a thump of revolver to my other palm -- then it's too skinny. A fatter bullet is needed! At the other extreme, if it takes more than moderate -- say, three or more pounds -- of pressure to get through -- then it's too fat, and needs to be resized -- I go ~ one thousandths at a time.
    Annnd, if it can be pushed through with the eraser end of a lead pencil using roughly two pounds pressure -- then -- (imho) it's just right.
    Nothing scientific here; and, I've never explored barrel diameter versus throat. I've many times slugged throats -- primarily to ensure all holed in a cylinder are the same size, as well as what it is. And, I've only has one revolver (a S&W Model 11 .38 S&W) which seemed to lead no matter what I did ---
    But... all in all... this is what I do, and has worked for me.
    geo

  9. #9
    Boolit Master
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    Quote Originally Posted by georgerkahn View Post
    [SIZE=3] "My" rule of thumb has been to take a sized, lubed, bullet, and drop it into a cylinder. If the bullet falls through by its own weight, or a thump of revolver to my other palm -- then it's too skinny. A fatter bullet is needed! At the other extreme, if it takes more than moderate -- say, three or more pounds -- of pressure to get through -- then it's too fat, and needs to be resized -- I go ~ one thousandths at a time.
    Hi George,

    This is an excellent example of direct measurement.

    Take care, Tom

  10. #10
    Boolit Master curioushooter's Avatar
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    "My" rule of thumb has been to take a sized, lubed, bullet, and drop it into a cylinder. If the bullet falls through by its own weight, or a thump of revolver to my other palm -- then it's too skinny. A fatter bullet is needed!
    Yes, this approach is no doubt sound, but I would prefer purchasing ONE sizing die an no others. That is why I want to know what the rule is regarding throats. The throats are consistently .432+ Should I get a .432 sizing die? Or a .433? Probably wont matter much.

    My M19 has a .357+ throat. I size those bullets .358 and they work great. Never bothered to check the bore on it because it shoots just fine. It is a P&Red Smith, however; the 624 is not.

  11. #11
    Boolit Master
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    If your technique is sound, then 0.432" is the correct diameter for your cast bullets.

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    Boolit Master
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    If that was the only 44 I owned, I would size to .432". Since all my other guns take a .431", I would use a .431". I don't know your own situation. You can fire lap your gun with a fire lap kit. It's kind of a PITA, but does work well. It will only lap your tight spot.

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    Unless you are going to clean after every cylinder full, measure / test after a shooting secession. (which usually changes the measurement.) And I have 5 sizers for 44 caliber because hardness & design affect the final diameter. If you shoot only 12 BHN or below, you can get away with one. Using a single size can lead to false conclusions about hardness & leading as you will often read here.
    Reading can provide limited education because only shooting provides YOUR answers as you tie everything together for THAT gun. The better the gun, the less you have to know / do & the more flexibility you have to achieve success.

  14. #14
    Boolit Master curioushooter's Avatar
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    You can fire lap your gun with a fire lap kit. It's kind of a PITA, but does work well. It will only lap your tight spot.
    How is that possible? My understanding of fire lapping and the nature of abrasives is that the most ABRASION will happen immediately forward of the case mouth (the throats). The abrasive will break down and be less sharp as it travels down the bore. This is why it works so well for rifles (which I have fire lapped many). It results in a slight taper from breech to muzzle since the abrasives cut the most at the breech and the least at the muzzle.

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    Boolit Grand Master Outpost75's Avatar
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    I'm with CuriousShooter on this one. Fire lapping causes wear of forcing cone and cylinder throats, but does little or nothing to mitigate a thread choke. A round-hole broach is the factory method to repair thread choke unless you pull the barrel, cast a lead lap and then uniform the barrel dimensions, chase the threads and reinstall the barrel, cementing with 242 Loctite so that the looser threads will stay tight without putting a hoop stress on the barrel.
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  16. #16
    Boolit Master
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    The fire lapping hits the constriction, which is pretty much right away. After that it will be sized down, and no longer effective. Do this enough times, and it should result as you say, in a slight taper from one end to the other. Most importantly, it can lap out the constriction.

  17. #17
    Boolit Master
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    Quote Originally Posted by Outpost75 View Post
    I'm with CuriousShooter on this one. Fire lapping causes wear of forcing cone and cylinder throats, but does little or nothing to mitigate a thread choke. A round-hole broach is the factory method to repair thread choke unless you pull the barrel, cast a lead lap and then uniform the barrel dimensions, chase the threads and reinstall the barrel, cementing with 242 Loctite so that the looser threads will stay tight without putting a hoop stress on the barrel.
    I only did it once to a blued steel S&W, and it 100% cured it. A pin gauge slides all the way through with no resistance. Cylinder throats were not effected, at least not significantly. I don't know about the throat, it looked fine to me. That gun is now gone, but it shot great after that. I hear stainless guns are a whole other deal, being incredibly hard.

  18. #18
    Boolit Buddy
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    Far from the expert, but depending on alloy, you might not get away with one sizing die.
    I know from my casting and sizing that a softer alloy (20/1 I use as this example) will not spring back and will be smaller due to this. My harder alloy WW + tin will spring back some. I measure with a good micrometer and not a caliper.

    Georgerkahn's method is what I do, more or less.

    Are you lubesizing or PCing your bullets is another good question.

    Good luck on the thread choke and I believe Outpost75 knows what he is talking about, but on some of the other forums experts have suggested doing the firelap drill.

  19. #19
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    I'm one who disagrees with the philosophy of "always size to the cylinder throats". I did considerable testing using a Ransom Rest and testing at 50 yards along with shooting off other rests at 25 yards found if the bullets were larger than .002 - over the barrel groove diameter then accuracy really wasn't improved and sometimes was worse. A lubed cast bullet coming out of a .429 groove diameter barrel is going to be swaged down to .424 - .427 because it also has to ride over a thin layer of lube. Thus a bullet starting out into the barrel .002 - .003 over groove diameter is getting sized down .005 - .006 under a lot of pressure very quickly. That can do some bad disfiguring of the bullet, especially the base.

    I also found with cylinder throats .003+ larger than barrel groove diameter a harder cast bullet that did not obturate .001 - .002 larger than barrel groove diameter gave better accuracy than a bullet sized .003+ over barrel groove diameter. I also find leading in the throat and barrel to be more a function of the alloy, lube and powder used than "fit" to the cylinder throats.

    Yes, I know many will disagree here but that's what I've found. I shoot .430 sized bullets in my Ruger and Hawes 44 Magnum revolvers with excellent accuracy and no leading. The Rugers throats are .432 and the Hawes are .433. I actually shot 5000+ cast bullets (COWWs) sized .429 and lubed with Javelina through the Hawes with excellent accuracy and no leading before I read I was doing it all wrong. Testing has shown bullets sized .431, .432 and .433 shoot no better (the .433 shot poorly as the barrel groove diameters are .429 in both revolvers) than the .429 and .430. I use .430 sized 44 bullets now simply because that size shoots best in my 44-40 Chiapa M92 which, of course, does not have cylinder throats.

    As to the "constriction" I have fire lapped a couple revolvers and it did work as with megasupermagnum. However, I've also found that simply shooting a couple hundred jacketed bullets with top end loads for the cartridge usually accomplishes the same thing.
    Larry Gibson

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  20. #20
    Boolit Master curioushooter's Avatar
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    I'm one who disagrees with the philosophy of "always size to the cylinder throats".
    Sometimes your hand is forced, Larry. In my case the throats were nicely consistent at .432+ (none would take the .433), but the only Lube-sizer dies available are .429, .430, and .431. So I got a .431 and told Arsenal to make me a Lyman 429421 clone mold that will cast at least .432 (probably their standard dimension).

    I had never really given much consideration to this until I read an article (by Brian Pearce) in Handloader. All I "knew" is that the throats better be bigger than the groove dimension, or accuracy will most likely disappoint.

    I've also found that simply shooting a couple hundred jacketed bullets with top end loads for the cartridge usually accomplishes the same thing.
    This was not a new revolver, and had lead fouling in the barrel when I bought it. It is a 44 Special (S&W 624, which is stainless) so factory JHPs are probably going to be not powerful enough to smooth it out anyway. Most factory 44 JPHs measure .429 and it is dubious if 44 special has enough pressure to obdurate them. The guy I bought it from was quite old and claimed to have taken deer with it years ago, so I figure he probably was a caster/reloader. After cleaning the tittle of lead fouling out of the barrel the pin gauge almost slipped past the "constriction" indicating it is indeed minor.

    Anybody consider the idea of applying the abrasive to the area of constriction and then firing a cast bullet into the abrasive? This would save the throats. It would also seem to be a bit easier than rolling the abrasive into the bullet with the steel plates.
    Last edited by curioushooter; 02-17-2020 at 01:47 PM.

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