Cast bullet accuracy comes from properly matched bullet diameter to your gun’s dimensions of throat, and groove diameter.

Slugging your bore to get groove diameter, and then adding .001-.003” more for bullet diameter is a good start, but does not address the key measurement: THROAT diameter.

You need to find throat diameter. This is the variable we try to address by adding bullet diameter excess to groove diameter. The trouble is, the “ extra amount” over groove diameter is only a guess. You need to take that variable out, and get an accurate measurement of your throat. Then select a sized bullet to just fit into the throat with a loaded round ( about 0.0005” less than throat diameter).

Take the guess work out. Save time, money, frustration with molds, sizing does, etc. Do a pound cast of your throat, and use that data for an informed decision on bullet diameter/ mold selection.

Veral Smith of LBT molds has info on his website for it.

Here is another link with a write up about making a “ pound cast.” If you are a cast bullet shooter, you should fully understand this concept. It take away most of the mystery of poor cast bullet performance.

https://www.artfulbullet.com/index.php?threads/article-2-how-i-make-pound-casts.131/

You can just drive an oversized muzzleloader ball (soft lead) into the chamber, and then back out again. Same result for a lot less hassle. I do that on every barrel I shoot cast bullets in; one ball to measure the throat and one more pushed all the way through to measure and feel the rifling.

Yessiree Bob. However you do it, it's critical info.

Please keep these tips coming. I was setting up to to do the complicated version of the pound cast when I saw this. You guys are great for sharing your knowledge and experience.

Glad to help. A tip for using a round ball, if it's not obvious - lube the ball and/or the bore with case lube. It doesn't take a lot, just something to keep it sliding easily. I use Hornady "Unique" case lube.

I have a lifetime supply of Cerrosafe, so that's the way I still do it. Typically I'll pour enough to include an inch of the chamber and an inch of the bore, which gives me neck, throat, and leade dimensions- everything a guy needs to know in one fell swoop.

It's probably pretty obvious, but clean the chamber and bore well before you slug.

Round balls work, but if you already cast making a throat slug out of a slightly larger bullet or mould works in throats and the bullet used in the bore works well for barrel measurements using pure lead.

Done and done. I am impressed that my new Marlin 1895 CBA has the same barrel dimension (.458) of my stolen Marlin 1895 Classic. That makes me feel better about the quality control of Marlin, which took a hit a few years ago. I am also relieved that my supply of .459 bullets on hand will not go to waste.

Again, thanks to all for the great advice.

I just seat the largest diameter bullet that will slide with a little resistance into the neck of a fired case. It seems to shoot well, lead little or none, and saves wear and tear on my brass.

Thanks, Dinny