Lapping a mold?

[quickdraw66]

I have a LEE mold that is slightly undersized for my 45 ACP, and I have read that pouring lead through a nut and using a wrench to turn it is a good way of increasing the diameter of the cavity. I had two questions though. What kind of lapping compound should I use, and how long does a process like this take? I need to go up 0.002".

[AggieEE]

Use fine valve grinding compound. To go up 2 thou you will need to cast a couple of laps for each cavity. So cast your lap. Put lapping compound on it turn in cavity, you may need to not squeeze too tight on the handles until it turns easy. Cast new lap, measure the cast so you don't go too far over repeat till right size. If the finish looks too rough to you, a final lap with Bon Ami or toothpaste should smooth things down nicely. Main thing go slowly and carefully. I never found a good "putback" tool to correct cutting too much. Good luck.

[rintinglen]

Those Lee Molds are soft. Take a look at this tutorial in the sticky section:http://castboolits.gunloads.com/showthread.php?257858-Expanding-a-boolit-mould-the-quot-WEET-quot-method-(In-parts) This works for steel molds

It is not a long, drawn out process at all.

I use Clovers Compound Fine grade, but any 280-400 grit polishing compound works fine. I prefer to bring the mold up to casting temperature, and cast two perfect boolits, making sure both have complete fill out. I then spread a thin coat of clovers about 3 inches long and just a smidge wider than the area of the boolit I want to enlarge on a flat piece of metal. I lay my boolit in the compound and then use another flat piece of metal to gently roll the boolit back and forth in the grit, gradually increasing the pressure to force the grit into the boolit metal. I take pains to keep the grit out of the lube grooves or any other place I don't want enlarged, wiping any compound out that gets in with a q-tip or the edge of a folded cloth or paper towel. Then I put the coated boolit in one of the cavities, closing it as firmly as I can with hand pressure. I drill a 1/8 inch hole about a quarter inch deep in the center of the boolit base (I have a cheapy Harbor freight Drill Press that works just fine). I screw a hex head 8-32 machine bolt in the resulting hole, and then use a 1/4 inch drive socket to turn the boolit, gradually until the mold will fully closes with gentle pressure. Clean the mold with mineral spirits or brake cleaner to get the compound off. I then coat the second boolit and do the next cavity.
Once they are both done, I clean the mold thoroughly with mineral spirits, and then cast and measure several boolits from each cavity. If they are too small still, I'd repeat the process, but that has not been necessary in the two molds I did this to.

[country gent]

Lapping can be a very precise process. cast several bullets You want from each cavity and also need to know which cavity they came from. I drill a hole in the base and glue a piece of key stock into it. 1/4" hole is just right for 3/16" key stock. Coat a bullet from cavity number one and lap num,ber 1 cavity working in a Tapping motion back and forth with rotation every 2-4 cucles do this 1-3 rotations. Move lapp to number 2 cavity and repeat the lapping process. WIth a lapp made from cavity number 2 slug start on cavity number 2 and then 1. Then another cavity number 1 and start in cavity number 2 follwed by number 2 cavity lap and starting in number1 cavity. This will result in very uniform cavities. .002 isnt much to remove as .001 on a side is .002 dia. I would work with very fine lapping compound in the 600-800 grit range. Flitz or shimichrome also are contenders for this. I have seen a guy use diamond compound but in steel brass or aluminum moulds its not needed.

[Walter Laich]

I've used the pour through the hex nut method. Use 600 grit. A couple of bullets each and I'm done most times. If you get in a hurry, time to quit; probably past time

[Yodogsandman]

So, is all the actual turning of the compound coated lap slug done by hand?

[docone31]

By hand, most times it has only been a couple of turns needed.