enlarging moulds?

I hope I’m not asking a stupid question.
I own a couple moulds for my Rifles (Rapine, Lee, Lyman). Is there a way to enlarge the mould (up to .002) without ruining the mould or having a custom mould made?
The moulds are Minies.
I’m not a gunsmith and my metalworking expierence and tools are pretty rustik. I’m looking for a ”žHomemade“ methode with accuracy ( =mission immpossible??)
thanks

Ken Clements said:

mission impossible??)
thanks

Click to expand...

Yes....... Alloys in casting lead will sometimes let the bullets shrink when chilled, but I can't think of a easy non-cost way of enlarging the bullet size or shrinking one with any accuracy. Swedging one on a cherry .002" larger is the only way I know, & making a perfect cherry for one is not an easy task unless you are a experienced blacksmith & have practiced doing so. IMHO

Some would say shimming the mold halved .001 on each side would do it, but then the bullet would no longer be perfectly round. How much dif that would make would be questionable, as I seldom see a perfectly round cast lead bullet anyway. Dealing with the shim each cast would most likely be a PITA as well, but you might try a SS shim & see if that works. A .001 shim on the mold half would give you .002 larger bullet in dia. on 2 sides, and this extra measurement diminish as you get on around to the original mold dia.

Keith Lisle

Keith, for just .002, what about lapping? On the other hand, I don't know if .002 is going to make much of a difference, even in a Minie.

Yes, it's been done before particularly for C&B revolvers where a tight fit is important to accuracy. .002" or even .003" is about the max.

The idea is to cast a ball or mini, screw "something" with threads and a shank (cut off wood screw) into it, place it back into the mold with course lapping dompound and spin it with a drill motor. It is time consuming and a little risky as you can possible exert more preassure on one block over the other and get it out of round. You also have to know when to stop.

A friend of mine just performed this trick for the bullet mold for his Vaquero, worked fine.

I lapped a Lee Minie mold using valve grinding compound. Like already described, I turned a screw into the minie, cut off the screw head and put it into a drill. It takes a while but now the minie does shoot out of my Lyman Trade Rifle. Before it would just drop down the barrel and I couldn't get any accuracy out of it. I had to use more than one minie because you are lapping the minie as well as the mold.

Depending on how much larger you want the mold to cast, you may need to cast new bullets in the enlarged size, as you increase the size of the mold through lapping, so that you can get it large enough for your needs. That means you not only use a couple of minies with each step of lapping, because both the lead bullet and the mold are ground by the lapping compound. You also have to stop, clean the mold, cast some new, larger bullets( they may be less than .001" larger, but that is why this is time consuming work) then lap the mold with these larger bullets to increase the diameter evenly some more.

The only problem I see with enlarging a mold for minie balls, is that hollow in the base. It removes a lot of lead you might need to give your wood screw total purchase on the bullet, where its needed most- back by the grease grooves.

I personally would cast some of those bullets with the hollow base stem removed, so I had a flat-based bullet to drill my hole into, and then run my wood screw into the hole, giving the support needed to enlarge those "bands" on both sides of the grooves. :hmm: :thumbsup:

You could bead blast it & do the same thing.. but it will not be even. When you lap it with lead, the grit is going to imbed into the lead unevenly & then not give you a true round surface. Also metal is going to build & make the ? lapping lead uneven. IMHO.
Yes, it could be done like this, just depends on how true you want it to be.

Keith Lisle

True Keith, but he's only wanting .002. I don't think .001, or even .002 out of round on a Minie bullet would affect accuracy enough to measure. I could be wrong.

If the ball is spinning in the drill chuck, how can any difference in the depth of the grit in the lead cause an out-of-round mold?

It seems to me that the high side will cut more steel than the low, and in the end you will get a mold that is even more ROUND than it might have been when it came from the factory.

You do have to recast new balls, or bullets, in the ever increasing diameter mold, not only to help in the lapping, but to allow you to do exact measurements of the ball/bullet to determine how much larger you have to size the mold to produce a ball/bullet that fits the gun. Even increasing the diameter .001" will help round out such a bullet mold. [ For the general information of other readers, lapping is something that is often measure in 10,000ths of an inch- not thousandths! It can require a new cast bullet every 1-2 10,000ths of an inch to change the diameter that .001", depending on what metal is used to make the mold.]

IIRC from my university trade classes, linotype alloy (lead) has very little shrink, maintaining crisp faces on the type. I'm not sure if it would work for shooting, but might work for lapping in this case.

Paul

Yes. Wheel weights are another source of harder lead to use for this kind of work. Its hard to find any Linotype these days. I guess I am showing my age, even knowing what it is. I was trained in type setting using this type of lead, back in 1961.

I'll give it a try with the minie and lapping compound.
I'm really not worried about the time I need, thats why I call all of this "stuff" a hobby :wink:
Thank you very much for your help..I'll post any results

I presume that you are wanting to gain .002 because the minies are a sliding fit in your barrel and you want a snugger fit. If that is what you are after the easy way is just make a tapered plug for the base of the minie insert and give a light tap. It doesn't take much at all to pre-expand the base of minies by a few thousandths.

DennisA said:

I presume that you are wanting to gain .002 because the minies are a sliding fit in your barrel and you want a snugger fit. If that is what you are after the easy way is just make a tapered plug for the base of the minie insert and give a light tap. It doesn't take much at all to pre-expand the base of minies by a few thousandths.

Click to expand...

i'll try that, thanks

You will be suprised at how hard it is to lap off .002 inches.