sizing question?

[tking308]

Some I'm very new to casting and I've read sticky on here and more info and something just struck me as odd. From what I've read I understand that having a boolit .001 or more larger than bore diameter is a good thing for obturation. My question is, why have sizing dies that are for example .452 or even .451 for a 45acp? Wouldn't you more want .453 or greater? Or .430-.431 for 44 mag?

[.22-10-45]

Remember your case I.D. is going ot determine max. dia. you can use..you can only expand mouth so far before case starts sticking in chamber. Then too..the tough brass tends to spring back after expanding and will size a lead bullet smaller. In revolvers..the cylinder mouth dia. is the determening factor. The old lead-bullet rifle masters such as H.M. Pope, Zischang, etc. knew an oversized bullet would tend to extrude fins on bullet base...the "stearing" end..destroying accuracy...that oversized lead has to go somewhere.

[scottfire1957]

Not all chambers and barrels measure the same from gun to gun, even in the same brand and model, much less from different makers. Or so I've read.

[tking308]

Remember your case I.D. is going ot determine max. dia. you can use..you can only expand mouth so far before case starts sticking in chamber. Then too..the tough brass tends to spring back after expanding and will size a lead bullet smaller. In revolvers..the cylinder mouth dia. is the determening factor. The old lead-bullet rifle masters such as H.M. Pope, Zischang, etc. knew an oversized bullet would tend to extrude fins on bullet base...the "stearing" end..destroying accuracy...that oversized lead has to go somewhere.

Not something I had considered, Thanks for the input.

[runfiverun]

22-10 brings up a good point.
I always advise to use a correct diameter boolit not an oversized boolit.
the rest of the slop needs to be taken up by brass. [or sumthin else]
cramming a tight fitting 313 boolit in a 308 barrel just makes things not quite work right.
I use boolits just barely over groove diameter in my rifles and have much better results.
,001 ,0015 fine, much more diameter and you lose much more than you gain.

[Slow Elk 45/70]

The semi-auto pistol is a different varmint than a revolver... most 45 auto barrel chambers won't accept boolits larger than .452... so you don't have a lot of variables in boolit size to play with some are happy with .451 , others like the .452

Now go to a 45 cal revolver.....the cylinder size has to be determined at the mouth...the barrel has to be slugged to see if it will accept the correct size boolit for the cylinder....older 45's were sometimes .452 others .454 if the loaded cartridges will chamber in the cylinder, the barrel will usually shoot them without blowing up the gun. THIS IS A SHORT STORY OF A MORE COMPLICATED PROCESS. a PLACE TO START, GO TO THE THREADS AND STICKY'S....hope this helps good casting and shooting. As stated .001-002 is the accepted norm.

[Linstrum]

I have a Citadel 1911A clone .45 that can only run 0.0005" oversize. That is half a thousandths of an inch aka 5 ten thousandths of an inch. It is pretty picky about boolit size, 0.4515" being its "sweet size" or compromise between not leading terribly and still having the cartridges feed without jamming the slide just short of being safely in-battery. Because of leading problems, that pistol requires a walking a "tight-rope" between brass choice, powder choice, and boolit size using cast. The "tight rope" probably consists of brass wall thickness in combination with boolit size so the cartridge case mouths fit the head spacing area of the chamber without jamming while the boolit base is still large enough to obturate and prevent gas cutting that causes barrel leading, with a powder that helps upset the slightly-small-for-cast-boolit-base so it assists with the obturation process. There is nothing simple about it, which is why I refer to it as "walking a tight rope". I little off on just one component of that critical mix and functionality does a nose dive with everything going to pieces with bad leading problems or the pistol jamming. But when it shoots, that pistol is flawless and almost as accurate as a rifle, I can hit a rifle target at 100 yards with it by walking my shots in. I would NOT want to be IN FRONT of that pistol at 100 yards! For the record, I use the Lee truncone TL452-230-TC, round nose TL452-230-2R (for my particular barrel both sized to 0.4515") and Auto Comp powder. The Lee 452-228-1R jammed and wouldn't feed no matter what I tried.

I'd better add that the engineering reason why the boolit size for my particular pistol can only be about 0.0005" larger than the slugged bore size is because the chamber diameter where the cartridge case fits cannot tolerate a cartridge case that is bulged from having a "fat" boolit stuffed into its mouth. If the cartridge is bulged from having a boolit that is 0.001" or 0.002" larger than the bore size, as may be ideal, then the cartridge won't easily slide into the chamber and the gun won't load! Can't shoot a gun if you can't load it! Many high powered rifles have tapered cartridges and chambers and powerful camming action bolts that push a cartridge in pretty darned hard and pull a cartridge out equally forcefully so the rifles work in dirty muddy conditions, so you can get away with having boolits 0.002" or even 0.003" over bore dimension where the cartridge necks are a press fit into the bore throats, but pistols, especially accurate pistols, by comparison may often be a bit "dainty" in the mud toleration department, and hence have a closer, tighter, smaller, range of fits where everything works just right. Because of that, a different mechanism is needed to prevent gas flow, and that mechanism is the sudden gas pressure from a fast powder resisted by the inertia of the boolit causing the boolit base to mushroom slightly so fits tightly inside the bore, filling in around the rifling grooves before gas cutting builds up and causes a major leading problem. If you look on the bottoms of some recovered non-gas check boolits, you will see the imprint left by powder grains where the powder gas pressure build-up pushed the grains into the lead alloy before the grains burned! I used to tape a dime on the backside of a 10 gauge shotgun slug and shoot the slug into a pond where I could get the slug back to show to the kids, and the dime was pushed deep into the metal of the slug base showing how hard the gas pushes on a bullet base!

rl 1,220