Sizing Cast Bullets

[noylj]

I have found that, for my purposes, sizing of my cast bullets does not produce a more accurate bullet and I shot as-cast. Likewise, I find that barrel leading is reduced using the "over-size" bullets and a quick tumble lube with liquid Alox.
However, I did hear an interesting thought about sizing cast bullets:
One should size to 0.001 inch under the inside diameter of the case mouth of a fired case.
This is an interesting idea, but the 0.001 inch sounds as though it might be too tight. Do any of you use a similar method to determine bullet size?

[462]

"Do any of you use a similar method to determine bullet size?"

Nope. I slug cylinder throats and barrels.

[geargnasher]

I'm with 462. I measure the gun, size for what I think it will need, and adjust only if the gun tells me otherwise, which isn't very often.

Sizing is one variable I can eliminate, and EVERY boolit I shoot gets sized. If the mould doesn't allow me to cast at least.0005" over my sized diameter, I get a different mould.

If the gun, revolvers in particular, have dimensional problems (barrel restrictions, especially at the forcing cones or cylinder throats smaller than groove diameter, for example), then the gun gets fixed or sold.

Gear

[Doc Highwall]

When you size bullets it should be larger then the diameter of the barrel of a rifle not the cartridge case. My 308 Win slugs at .308" and I size my bullets at .310" and going to try .3105" when I get a chance.

[Bret4207]

Some time back Uncle Felix recommended measuring the case mouth ID from a load fired in the particular gun with a a full power load. I've found in most cases that is the size I end up using. It's the maximum size you can still chamber. Usually it relates closely to throat size.

IME going larger results either in difficulty chambering or boolits "squished" in seating/crimping. There are odd guns that end up with an oversized forepart and reduced body within the neck, but I haven't had a lot of luck with that.

I don't believe in sizing for sizings sake. I do use a slightly oversized sizer for lubing/GC seating. IMO any sizing runs the risk of damaging the boolit, to what extent is hard to say, but the risk is there.

[runfiverun]

sizing fun questions.
in revolvers i go as large as possible.
the measuring a fired case is just to give you an idea how large you can go.
don't do much good to put a 432 boolit in a case and it won't chamber on the other hand if it will take a 432 then it certainly won't hurt to use that size.

as far as levergun chambers and rifle loads go boolits can be sized to the bbls dimensions.
a slip fit i call it.
most newer rifles have shorter throats and leade angles allowing the use of smaller than traditional diameters.
for example i use 2245 in my 223 rem and 323 in my 8 mauser.
you don't have to be excessively large, correct sized is fine.

[JIMinPHX]

I think that measuring the mouth of the fired brass is irrelevant. That will vary with the chamber diameter & brass thickness. It has nothing to do with the barrel dimensions.

That is...it's irrelevant unless your chamber is so tight that a loaded round will not fully enter the chamber without resistance. You do need a little clearance in the chamber so that the brass can open up & let go of the boolit.

[qajaq59]

I size everything. There are enough variables in cast bullets already, so that simply eliminates one of them for me. Plus, I can lube, size, and put the gas checks on all at the same time. But that's just my way. There are plenty of others.

[geargnasher]

+1 Qajaq59.

What ever works for you is what works.

The point that is often overlooked when selecting a boolit mould and a sizer for a particular gun is that the critical dimensions of the whole gun be considered. That means partial and full-length barrel slugging, doping out bore restrictions, measuring forcing cones and cylinder throats as well as all the chambers in a revolver, doing "dummy round" setup in automatic pistols, and doing chamber casts or impact slugs of rifle chambers/throats. All these things need to be considered, and, while we often disagree on what the "rules of thumb" are for sizing to the measurements we get from our guns because each gun is it's own animal, we can at least recognize that things like chamber, leade, cylinder throat, groove AND bore diameter, cartridge neck thickness, velocity, alloy, pressure, etc. ALL have to be taken into consideration if we want the best results possible from our casting and reloading efforts.

Bret, I think you might be taking what Felix said about sizing to a fired case mouth a little out of context here. We both know why he said that, but that is far from the whole story about considering that dimension. We do need to know our chamber neck dimensions and brass neck wall thickness so we know our boolit diameter limit, but that's not necessarily the dimension I use to determine boolit size. Most of my rifles have been happy if I size right at or slightly over groove diameter, depending on pressure and a million other things. My .30-30 at 2000 fps likes .003 over and a softer alloy, like ACWW. My Model 70 .30-'06 has never been fired with jacketed (except proofing) and has a tight leade and chamber. I use Military brass with thick necks, turn them slightly, size .3085" with water-dropped 50/50 WW/pure plus a pinch of tin, and fire them to well over 2500 fps with good accuracy. The gun will chamber a .311" boolit no problem with Remington brass, but doesn't shoot worth a hoot. A chamber cast (done a few years ago before I discovered this forum and the impact slug method) revealed the dimensions I needed to use to select a mould, brass neck thickness, and seating depth. Those measurements saved me a lot of time and enabled me to do with the gun what a lot of people haven't.

Again, each person must do what they feel comfortable with and what their guns like, and we also must recognize that we often get conflicting results from using the "same" methods.

Gear

[fredj338]

I'm with 462. I measure the gun, size for what I think it will need, and adjust only if the gun tells me otherwise, which isn't very often.

Sizing is one variable I can eliminate, and EVERY boolit I shoot gets sized. If the mould doesn't allow me to cast at least.0005" over my sized diameter, I get a different mould.

If the gun, revolvers in particular, have dimensional problems (barrel restrictions, especially at the forcing cones or cylinder throats smaller than groove diameter, for example), then the gun gets fixed or sold.

Gear
I agree. The other reason I like to size all lead bullets is to get uniform neck tension. It certainly can't help accuracy if bullets vary from say 0.451"-0.453", neck tension will vary quite a bit w/ that & that affrects crimp & powder combustion, JM2c.

[Bret4207]

Guys, unless we start reaming or turning necks the max ID of that full power case is as large as we can go without distorting the boolit. I've tried this in a mess of guns, it seems to be where I end up. Of course it varies from gun to gun and from make to make on brass. Every gun is an individual. I'm just saying that it's proven out everytime for me so far. I prefer +.002 or maybe a bit more over groove. So far that's where I've wound up every time using Felixs suggestion. It's not a cure all, but a darn good starting place for those unable to make chamber casts or who get a bit nervous at the thought of making impact slugs.

[knappy]

I have found that, for my purposes, sizing of my cast bullets does not produce a more accurate bullet and I shot as-cast. Likewise, I find that barrel leading is reduced using the "over-size" bullets and a quick tumble lube with liquid Alox.
However, I did hear an interesting thought about sizing cast bullets:
One should size to 0.001 inch under the inside diameter of the case mouth of a fired case.
This is an interesting idea, but the 0.001 inch sounds as though it might be too tight. Do any of you use a similar method to determine bullet size?

I allso like to do cylinders throats and barrels get a better fit