Optimal inside case diameter for cast bullets?

[burbank.jung]

Is there an optimal inside case diameter for cast bullets? Would 0.001" be adequate for handguns?

I started a thread on another forum about using the expander plug of a .38 in a 9mm case to expand the case to accept my cast bullets that are swaged to 0.357' because my bhp barrel swages to 0.356". I removed the expander plug from my .9mm RCBS expander plug and measured it at .352" with a slight 0.001" taper leading up the flare. The .38 Special expander plug measured 0.355 and tapered to 0.001" to the flare. So, it enlarges the mouth less than 0.356 because the mandrel is long. I have two reason for doing this. First, I come across rounds that won't feed into my chamber. I think that the diameter of the bullet and the thickness of the case is the cause. Secondly, I don't want to swage my cast bullets in a case that is too tight. Note, I did seat bullets in an R-P Case and ran another through a Lee FCD. Using a Kinetic Hammer to remove the bullets and measuring them, the size of the bullet was the same. In other words, the bullets did not swage. BTW, the bullets were cast from range lead. Do you think I'm on the right track to assemble a more accurate load?

 

[Spindrift]

I have no experience, reloading for handguns. For my rifles, I use 0,001-2 in of neck tension. Preferably 0,001 for lubed, PB bullets- gas checked bullets (and coated PB) seem to handle 0,002in tension with no issues. If your original expander leaves 0,005in of neck tension, this seems excessive to me.


In a self-loading firearm, a proper crimp will be required I suppose.

 

[Petrol & Powder]

I’ll address the expanding function first and address the flaring portion of the operation second.

When speaking about handgun cartridges that utilize straight-walled rimmed casings (like 38 Special, 44 Special, etc.) a good place to start is an expanded diameter that matches the bullet diameter.

The brass casing will experience a certain amount of spring back when the expander is removed. So, whatever the diameter of the expander is, the resulting inside diameter of the casing will be less than that when the expander is withdrawn. How much less? Hard to say, not all brass is the same. However, there will be some neck tension and this method provides a good starting point. In fact, it generally results in a good finish point as well.

The expander also needs to project deep enough into the casing to match the portion of the bullet that will be seated in the casing.

NOW, moving onto the “flaring” portion of the expanding operation. When using cast bullets, the Lyman “M” type profile really shines. It doesn’t have to be a Lyman expander; they are just the ones that named the profile. What we are talking about is the last portion of the expander that enters the casing and expands the case mouth to accept the bullet without shaving lead. The Lyman “M” type creates a “step” and does not funnel the case mouth like a trumpet bell. This is accomplished with a portion of the expander that steps up to a slightly larger diameter than the main portion of the expander. It aint’ rocket science.

If we’re dealing with rimless semi-auto casings (most of which has some taper), it gets a little more difficult. With 9mm Luger, it can be downright frustrating. 9mm barrel dimensions are allover the map, so the starting point will depend on YOUR gun’s dimensions. You may or may not need a bit more neck tension (without swaging the bullet down in the casing) and the Lyman “M” type step is still useful. But you may need to experiment to find the sweet spot for neck tension.

Good news here, if you have a Lee universal expander die body, N.O.E. makes expander plugs that work in that die body. N.O.E. expander plugs are available in LOTS of sizes.

 

[Bret4207]

I'm a little confused on exactly what you are asking for. Do you mean neck tension as Spindrift alluded to, or do you mean neck ID as compared to bullet OD? Or are you referring to neck wall thickness in relation to either of those? It's all inter-related, but they're separate discussions that come together in the end. You don't want your bullets swaged undersized for sure, but you need a certain amount of hold on the bullet, sometimes more than others. How you get there comes from at least the 3 things I mentioned and likely more. IME "optimum" conditions vary from gun to gun and bullet/powder/case/etc in that gun.

ETA- and there are probably some who would note that it's not going to matter much as long as you put enough pressure on the bullet to cause it to obturate enough to fill the throat!

 

[Glaciers]

I’ll second the NOE expander plugs in the LEE universal die body, verity for just about any diameter needed. Especially important the softer the casting. The NOE plug has that second step for a slight flair.

 

[Snakeoil]

Back when I was shooting pistols seriously, I used strictly commercially made cast bullets that were very hard and had a beveled base. All were loaded in a Dillon Square Deal B which full length resizes every case. Standard for good accuracy out of my Wilson Combat 1911 or my Springfield Armory 1911 was 2 inches at 50 yds and I was always able to achieve that. I realize that range scrape varies so anyone's guess what the hardness is. Used the same process for .38spl light loads and .357 hot load shot out of my 586.

Later, when I started shooting CAS, again, same process used for .45LC shot out of 4-3/4 and 7-1/2 Colts SAA's.

Never encountered any issues with leading that were not expected over time in full house .357 loads and .45ACP loads. And the leading was not bad. I'd scrub the barrels more out of habit than out of a need due to loss of accuracy.

 

[Charles Graff]

Well, it depends on how hard/soft are your bullets and has fast/slow is your powder. In revolvers, I use fairly soft bullets and fast powder, so the same size as the bullet or no more than .001" under bullet size.