45-70 cast bullet size

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gerardjohnson

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Usually cast bullets are up to .002 larger than the jacketed of the same calibre. Why are 45-70 molds mostly .457 when the jacketed bullets are .458? Most Lee molds are .457 except 2 that are .459 diameter. What is the reasoning here? Also, what is the purpose of a hollow base?
 
The mixture (ratio of tin to lead) will determine the size of bullet the mould will throw.
The hollow bottom is so on firing the bullet will bump up in size and grab the rifling better.
Ken
 
Hollow base bullets are designed to expand on firing, and seal the gasses. It was originally for Black powder.
As to mould sizes, what you see on the mould is not always what you get either. Moulds vary, and your alloy will change size as well bullets shrink as they cool, and some alloys shrink more than others. With my wheelweight only melt, my Lee moulds run about .458 or a tad more, my Lyman moulds are slightly under .458 with the same melt.
 
I make damn sure that the bullets drop out of a mold at .460" or the mold isn't much good, I find that most 45/70s do best with .459" but one should slug their bore to be sure. Lee molds don't hold the tolerance to any great degree and they vary in size and some are really small(.457 or so). The NEI, Paul Jones, Hoch, Saeco, RCBS, Lyman molds that we use all come in at .460" or larger and can be tailored to the individual gun.
 
John Y Cannuck said:
Hollow base bullets are designed to expand on firing, and seal the gasses. It was originally for Black powder.
As to mould sizes, what you see on the mould is not always what you get either. Moulds vary, and your alloy will change size as well bullets shrink as they cool, and some alloys shrink more than others. With my wheelweight only melt, my Lee moulds run about .458 or a tad more, my Lyman moulds are slightly under .458 with the same melt.
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X2, agreed. Using cast bullets in that calibre range what has worked well for me is a sizing of 0.001" - 0.002" over bore daimeter.
 
Hollow base moulds are much harder to use(get good fillout) and much slower(single cavity) to make bullets. I have heard of problems with these designs if the skirt is too thin and comes apart on firing. These were designed long ago to allow use even when Black Powder fouling wouldn't allow chambering of boresize bullets. To this day they are most effective with black powder and usually not as accurate as proper bore size bullets.
 
gerardjohnson said:
Usually cast bullets are up to .002 larger than the jacketed of the same calibre. Why are 45-70 molds mostly .457 when the jacketed bullets are .458? Most Lee molds are .457 except 2 that are .459 diameter. What is the reasoning here? Also, what is the purpose of a hollow base?
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You need to worry more about the measured diameter of your throat and ball seat than what the mould supposedly drops or what is "supposed" to be the best diameter for that particular caliber. Slug your firearm or do a Cerrosafe casting and then measure.

Bottom line: you want the bullet diameter to match ball seat/throat diameter -.0005" or thereabouts for best results. The bore diameter doesn't matter one little bit: when the bright light appears underneath the seated bullet, trust me on this, the bullet will size down as necessary to achieve bore diameter as it enters it from the throat. However, if your ball seat/throat diameter is much bigger in size than bore diameter and you try matching bore diameter, you are setting the stage for accuracy and possibly leading problems.

I generally have my rifle moulds throwing throat/ball seat diameter +.002". Sizing .002" does not seem to make an appreciable difference to bullet quality, including in cast bullet benchrest matches. And having that bullet .002" oversize to begin with allows some latitude as the throat/ball seat of the rifle it is being used in wears over time.

Robert Stillwell will make sizing dies for you that will size to just about any diameter you want, and he does it for an extremely affordable price.

Hollow base bullets have been around for a variety of purposes. One is to have a skirt that allows a relatively loose bullet fit, yet one which will obdurate to seal the bore and grip the rifling when fired. Another reason was to provide a space for the twist to go when paper patching bullets. There are probably other reasons as well.
 
I use the largest diameter bullet that will chamber, the chamber "neck" diameter being the limiting factor.
 
John Y Cannuck said:
That's a good point Andy, I have a 44-40 that won't accept anything much larger than bore size due to a tight chamber.
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If it shoots well - great. If not, you could:

- use softer alloy and faster powders and try to get some bullet obturation;
- inside neck turn your brass;
- "heel" your bullets; or
- open up the chamber a bit.
 
John Y Cannuck said:
That's a good point Andy, I have a 44-40 that won't accept anything much larger than bore size due to a tight chamber.
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Tight chamber or not, if your bullets are cast/sized to just chamber, then you're on the right track (at least, regarding what a lot of us view as important with regards to velocity, accuracy, and a lack of leading). Bore size bullets sitting in much bigger throats/ball seats at the moment of firing are not what I consider a recipe for success.
 
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