I though I knew how to slug after much experience but this one has me scratching my head.   In gripping the slug with the jaws of the caliper I always have sought the middle of the groove (= greatest diameter and =groove diameter).  Doing this gives a reading of .368.  However, with this one as you rotate the slug within the jaws (seeking max) and approach the juncture of the groove and land the caliper reading consistently reads .373.

Do I accept .368 for groove or do I go for the largest reading =.373 as the basis for ordering a mold?

Pope type grooves are the extreme of what you are seeing.
If looking for a groove diameter bullet, use the smaller and hope it bumps up.
Otherwise use the larger diameter.
Someone with Pope groove experience might have better suggestions.
Chuck

A caliper is not the best way to go, you need a real micrometer. You'll probably find that the groove diameter is more like .367 as it should be. There will also be an even number of lands/grooves so just measure straight across - land to land or groove to groove. Order 37-196B or 37-196BG or 37-175C from Accurate moulds. They all have the same nose profile. Tell him your alloy and whether you want it to cast .367, .368, or even .369.

Premod70 wrote on Jan 22^nd, 2019 at 7:31pm:


Has even number

I agree with oneatatime that a pair of dial calipers is definitely not what you need for measuring bullet or slug diameter. Micrometers are the only way to go. I've always turned my slugs while adjusting the micrometer to see what the largest diameter is. I check bot groove to groove, and also corners of the grooves too. Then determine my bullet diameter based on both readings. If you're shooting BP the smaller of the two works fine, but with smokeless powders I prefer to size to the larger of the two readings.

I think we know what you were saying - for that largest measure you are measuring from one edge of the raised portion of a bullet to the same edge on the opposite side of the bullet. What you want to do is measure from the top of the raised portion to the top of the raised portion on the opposite side. Remember that if your bullet starts at that diameter that the lead that was in the "grooves" of the fired bullet had to go somewhere - either into making the large diameter larger or forming tails on the rear of the bullet behind the grooves.

Pic 2 Rotated slightly to near junction of land.

svartkruttgris#369 wrote on Jan 23^rd, 2019 at 7:49pm:


It's exactly how Pope did his famous rifling.