How Ball Molds are Sized?

[mckaylodge]

Still a newbie.
I cast non-lead alloy from Rotometals for my Pedersoli 20 ga. Howdah and that alloy does not shrink so I use a Lee double 0.60 (as rated) mold for making non-shrinking alloy balls for the Howdah 0.6288 (actual) barrels. The non-shrinking balls coming out measure a little larger than 0.60, ranging between 0.6020-0.6075. So they are a good fit for the 0.6287 barrels. I am using 0.01 patches now but could go thicker.
I now need a mold for a Pedersoli AN IX barrel measuring an actual 0.6880 in. using this alloy.
So, do I need to find a mold that will cast no larger than about 0.66 if I can find something.
That is, I need a mold with a cavity measuring about 0.66.
Would a mold identified as a 0.66 mold (if one exists) produce a 0.66 lead ball after shrinking and a larger ball if used with a non-shrinking alloy?
Put another way, would such a mold identified as 0.66 have a cavity measuring 0.66 or a larger cavity to accomodate the shrinking of lead so that it results in a lead ball measuring 0.66?
What mold identification in caliber would you suggest from available sizes that would produce a non-shrinking alloy ball close to 0.66?
Thanks

 

[mooman76]

A little confused but I think I know what you are getting at. Black powder moulds are suppose to be made to size when casting pure lead. That being because that is what is typically cast for BP. Alloyed lead will come out about .001 or .002 larger because alloy does not shrink as much. That being said the moulds for modern guns are suppose to be cut for use with alloyed lead. Problem with that is that some moulds like Lyman are cut with a cherry and as the cherry wares down the mould comes out smaller and smaller. I don't know if they still do but for awhile Lyman kept reusing their cherries to the mould that the bullets cast would sometimes come out too small.

I believe most of the aluminum moulds like Lee are cut on CNC laths. It is my understanding that Lee presses a steel ball into the RB moulds when finished to get an exact size all the time. Tanner in England makes RB moulds any size you want and I hear they are very good.

 

[Loyalist Dave]

Would a mold identified as a 0.66 mold (if one exists) produce a 0.66 lead ball after shrinking and a larger ball if used with a non-shrinking alloy?
Put another way, would such a mold identified as 0.66 have a cavity measuring 0.66 or a larger cavity to accomodate the shrinking of lead so that it results in a lead ball measuring 0.66?
What mold identification in caliber would you suggest from available sizes that would produce a non-shrinking alloy ball close to 0.66?
Thanks

The mold is made so that when the ball is cooled it gives you a ball very close to .660

YES if you use alloy, the ball will be larger

No mold made for pure lead round ball casting will give you an alloy ball close to .660 without experimentation, because the alloys are different.
Tin is added for easier melting and pouring and antimony is added for increased hardness. There is no real standardized "bullet alloy" and some folks like to remelt once shot modern lead (lead alloy) bullets, but if you get a person who is a hand caster and pushing his cast bullet to upper speeds, the bullet may be made out of old weight alloy, or even harder linotype alloy. IF you have a person complying with Kalfoяиia no-lead-bullet laws, then the alloy is likely tin and bismuth.

LD

 

[necchi]

1st. Measuring a sphere with dial calipers or micrometers to 0.00 tolerance is really hard to do as the apex of diameter needs to be checked at multiple angles and rotation then averaged.
2nd. Actual cast ball consistency can be better checked (with a good scale) by weight. Ball diameter can remain consistent but a weight variable can/will indicate a random "void" (air bubble) in a cast.
3rd. As moonman76 pointed out, mass manufacture of molds lend to individual molds in a the process being slightly different.
4th. I just measured a single hair from my beard (ouch!) It's .0035. That, is nearly indiscernible from your .0055 tolerance for diameter of your cast ball.
5th. You mentioned patch thickness,, and that you could change that, and that's the key.
Patch thickness is a variable easily controlled.
I have learned that Consistent ball by weight, then consistent patch thickness and lubrication can lead to reliable accuracy.

Point; dissecting cast ball diameter for a smooth bore as the variable to the 0.00 or less isn't going to gain much.
Tip; Buy a mold that has a return option. If it casts inconsistently, send it back. If the cast is fine,, then change the other variables to find the accurate load.