Slow learner

[gasboffer]

I've been loading for rifles for about 52 years and have had some success with producing accurate loads in bottle-neck cases. I learned early on that an accurate load requires a relatively snug fit of the cartridge case in the chamber.
I recently acquired an EMF in .357 mag. Accuracy ran from pretty good to mediocre with all loads tried, and I tried a bunch! With cast bullets, I was getting leading in about the first inch of the barrel, but just on the bottom half of the bore.
Then, a vision came to me! I measured the fired cases, .357 mag., came out at .376". Cases sized in a carbide sizing die measured .371. Cases sized in a steel sizing die (RCBS both) measured .375". Winchester factory .357 cases measured .375"
I assume that a case .371" in a .376" or larger chamber will be lying on the bottom of the chamber with a relatively large empty space over the cartridge case. The bullet will start out hitting the lower half of the bore, causing the leading.
I loaded some unsized fired cases using just the expander/belling die. The bullet, .357", was a relatively tight fit in the unsized cases, and is roll crimped into the first band.
I'll be testing out this theory the first day the wind isn't blowing 35 mph in West Texas.
Any gurus out there have opinions on this hypothesis?
Clyde

[DLCTEX]

At the least there is potential for the boolit to start out skewed, leading and/or gas cutting are sure to follow. You don't state the maker of the carbide die, but if its that much undersized, I'd contact the maker and give them an opportunity to make it right. Dale

[Char-Gar]

I am not a guru by any means, but I doubt if your theory will prove out. It may, who knows, it is new one on me. My money is on bad bullet fit or alloy.

However, don't full length size your cases. Size just enough to hold the bullet firm. That should keep your cases centered in the chamber and that will help accuracy, even though it may not help with the leading issues. You need to size the bullet area as you will need bullet pull to get good combustion and accuracy.

I lived five years in Odessa. Both my kids graduated from Permian HS and my ex-wife still lives there. I can't say, I would like to live there again.

Keep us posted, I would like to know how this works out. I am always interested in learning something.

[Glen]

If the cartridge is laying on the bottom of the chamber, then as it angles up to sit in the throat, the bullet will hit the top of the bore, leaving a gap in the bottom, and the gas blow-by will cause leading, so both you and Chargar are probably right. Fatter bullets and fatter cartridges are called for, I suspect.

[Bass Ackward]

I assume that a case .371" in a .376" or larger chamber will be lying on the bottom of the chamber with a relatively large empty space over the cartridge case. The bullet will start out hitting the lower half of the bore, causing the leading.



Clyde,

As a theorist, you sound like a man that wants to solve this himself. Chargar gave you a way to test it. Proof of the taste.

I will say this. If Congress ever made .... "slugging your throat" (and bore) before you can pull the trigger on a cast bullet a law, this WEB site would have to close several rifle catagories.

But never fear, handguns can still drive ya nuts though. :grin:

[44man]

Bass, thats the reason I neck size my revolver cases! There is no need to full length with a carbide die (I like the Hornady TN die.) until a case won't chamber any more from hot loads. It is only when it takes a lot of thumb pressure to chamber a load, that I will full length that case. Verl Smith Has instructions in his book showing how to lap the bottom of a steel die so the very bottom of the brass is not sized so the rear will center. Most steel dies have a slight taper inside, so most need the case run all the way in so the neck is sized enough. It is very hard to neck size with a steel die although some dies are straight inside and it can be done.
The next thing you want is a throat fitting boolit that will enter the throat enough to center the boolit.
I would not worry about the .371 measurement unless you are shooting soft boolits. A hard enough boolit will expand the brass to what you need. If your boolits are soft, try different expanders so you still have the neck tension you want.
In a rifle for straight wall cases, the flare can be left on to center the front of the case too. I do that a lot with my 45-70.
I hear a lot of theorys about not needing hard boolits but I don't think my harder boolits shoot better because of what they do in the bore, but what the brass DOESN'T do to them. For the slow powers I use, I need neck tension that I can't get with soft boolits, I don't want boolits sized when seating and I don't want the crimp to scrape the boolit down in size as the boolit exits either. That crimp is a lot harder then the lead and all of the above are the reasons most guys get better accuracy from jacketed bullets.
I am able to match or exceed condom bullet accuracy.

[gasboffer]

Thanks, guys.
A lot of good information. I'll be trying all the suggestions. One other thing, I have a Lee 358158RF with a fairly large diameter nose. I can't seat it out far enough to come close to the rifling. (Won't feed through the action)
Clyde

[felix]

If you have to crimp beyond that necessary to just knock the brass straight from the previous belling step, plus a smite, then you are crimping too much. If the boolit(s) move during recoil, then make the expander button/bar incrementally smaller. It is best to crimp on the solid part of the boolit and let the crimp groove be filled with lube. Better yet, just have a boolit design with multi mini and very shallow grooves up on the nose for lube/crimping. Besides, these mini grooves will move the center of pressure and gravity back towards the base where they belong. ... felix

[lovedogs]

That thing about leaving the bell on your .45-70 cases (44man) is a good idea. I do that with my single-shot .45-70, also. Don't know if that has anything to do with it but the rifle shoots MOA at all ranges, which is better than any other
.45-70 that I know of. I leave enough bell that I can feel the drag as I put the round in the chamber... and all this time I thought I had a big secret for accuracy.