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How to lap the mould out a couple thou'

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19 November 2002, 23:36
How to lap the mould out a couple thou'
It was suggested that I " lap my mould out a couple of thou " to increase diameter and improve accuracy .

How is it done or is it done by a gunsmith / engineer ?

You may think this is a stupid question but it isn't covered in any of my books about casting .

20 November 2002, 02:12
Bad Ass Wallace
Lapping can be done very easily by using a previously cast bullet and coating it with valve grinding paste 350 grit. Firstly I use a Forster "hollow pointer" on a reversed bullet. Next tap a drill stub into the hole until it bites onto the lead and set up in a drill press with a speed of no more than 60-80rpm
Gently bring the mould halves into the polishing cherry and 2-3mins should complete it.
Finish polishing the mould with jeweller's Dilux polishing compound.
Note of caution: the mould halves can be held in the fingers BUT AT ALL TIMES sitting on the drill table which is wound up to suit the position of the cherry. Simply holding in the hand will result in the cavities and cherry not being aligned in the vertical axis.
20 November 2002, 05:05
I've done that to salvage rusted molds or to molds that would not drop bullets, but I was trying to remove as little metal as possible and used 800 or 1000 grit Clover Compound.

You say it works on alumimum, too?
20 November 2002, 13:18
Ben insert cast bullet into the mold and drill a hole into the center base of that slug. Check a drywall screw into your hand drill and allow this to thread into that hole. It'll tighten and spin the slug. Then remove that slug on the screw, coat the area to lap on the bullet with 240 grit or so lapping coumpound- insert and spin. Aluminum molds maybe 30 seconds or so. Clean the mold and cast to check dia.

Did both my Lee 45 caliber molds this way.
21 November 2002, 09:14
Thanks all
21 November 2002, 09:09
Heres' a good page on mold lapping.
24 November 2002, 03:04
Way back when, when the computers were still gas powered and we all walked thru 6 feet of snow to school, uphill both ways summer, winter, spring
and fall, there was an article about bumping up cast bullets.
The idea was to make a die to fit the reloading press,{7/8th 14} bored to the diameter that was desired. I'd suggest .460 for this caliber. There is a threaded stem at the top with some sort of punch out device. The length of the bumping chamber chamber was determined by the threaded stem at the top, the the punching out device knocked out the bullet once it's bumped up to size. There is a ram that fits into the reloading presses ram like a shell holder. This ram is snug fit to the chamber, in this case .460.
The cast bullet is lubed, filling the lube grooves with some sort of stick lube, Lyman's, RCBS,...home made? The lube keeps the lube grooves from collapsing while bumping it up to size.

Set the bullet on the ram and run it up into the
bumping up chamber applying a bit of pressure to swage the lead up to the desired size. You will need to tinker around with threaded stem at the top to adjust the length of the chamber, so as to get a bit of compression on the bullet.
Drop the ram, tap the punch out device and catch bullet. The bullet should be the desired size.
24 November 2002, 09:00

You best be using pure lead when you try that trick. And I'd want a Rockchucker or better press for it in that big a bullet.

Still, it's doable. Were I the one doing the doing, I'd look into modifying one of the Lee sizing dies. And several folks have built swaging dies for presses. They tend to be pricey, though.