Pedersoli ball mold - "Nominal" size ?

[wtilenw]

Then why the word "nominal" .310, why not just .310 ?
That's the question

take a gummy dude

 

[D Sanders]

I like to think I’m smart but I can’t figure this thinking mold size is mold size.
Does it have to do with shrinkage as different metals contract (shrink) differently as they cool?

YES. You hit the nail on the head. I'm a tool and die maker. Spent 35 plus years in die cast and plastic mold industry. Lead if cast from steel mold blocks, shrinks approximately. 005 to the inch shink rate. That means if you want to cast an exact 1 inch dia ball, the cavity in the steel block would need to be machined to 1.005 in diameter. The measured .310 diameter ball would drop from a cavity that is machined to .3115 diameter. (If machined correctly). This the lead shrink rate I use when making my bullet molds. And yes different alloy lead will not shrink the same. If you saw the word "nominal" they are probably telling you they are not responsible for the the different variables that happen with casting such as mold block / lead temperature and alloys. All of these things make a difference. If you are new to bullet casting, you will quickly find this out. When you purchase a ball/bullet mold, the stated diameter number is the size of the projectile that you want to end up with when it cools. Hope this helps.

 

[tenngun]

Why is the 'nominal" size of a 2x4 actually 1 1/2 x 3 1/2 ?

It was a rough sawn 2x4 at one time. But that’s just the setting on the saw. They might be 2 1/4 on one edge, 1 7/8 on the other. And pretty rough as they’re cut with pretty rough saws.
So in a planer they go. 1 1/2x 3 1/2 cleans up every board no matter how rough.
I wonder if nominal on the molds points to ti being ball for a .32 or .36 or .62, even though we shoot a .310 or .350 or .600 it’s the nominal size for a particular caliber