Identify Brooks bullet mold bullet size

[keweenaw]

Hello

I have a steve brooks bullet mold that produces a smooth sided paper patched design bullet. Got it from a guy who was shooting a Pedersoli Gibbs, so I presume it will be around .451 with the paper patch, but not exactly sure. I am planning on selling it as i have no need for it now. But how to identify the bullet size. Only markings are 12 and SB. Has a shallow base plug attached. Any ideas?
Thanks

[Hal]

Hope I'm not being too obvious, but I would just a cast a few and measure them, then state the size as dropped and from what alloy. I would think that, in conjunction with pic and description that it is for paper patching, would be enough info for someone to make a decision.

[rmark]

A paper patch bullet for a .451 muzzleloader should cast about .443 assuming .002 thick paper double wrapped damp. Measuring the base of the cavity inside the closed with a caliper might work, measuring a bullet cast from soft lead would be better.