While the subject of mould lapping has been covered in the literature; I am so pleased with my results that I would like to describe what I did.
My first ever attempt was last week with a damaged mould that I described here.
The little Ideal 257382 was already one of the best casting moulds I've ever owned but after I lapped it enough to get it clean; it positively started “auto ejecting” bullets. I mean if the bullet didn't fall out when I opened the mould all I had to do to get it to drop was turn my wrist a bit.
That brings me to today. I played hooky from work this afternoon and planned to cast some bullets with my RCBS 150CM. This .30 caliber bullet is one of my favorites and has shot well in the 30-30 .308 and 30/06.
The mould itself is another story, it has always been aggravating to use. I've tried every thing I've read about or thought up trying to get it to release bullets. I believe it may have been cut slightly off center because the bullets always hung up on the same side of the mould. The squarish grooves do not help much either. Every cast required 3-5 hard hits to the hinge pin, with a fair size mallet, to make them drop. This is frustrating as we all know and I know for a fact that when I'm frustrated I'm not casting bullets to the best of my ability.
Well, today I decided to try lapping out the RCBS to see if it helped any and boy did it. One light tap is all it takes now. I cast about 200 bullets and it just kept on spitting out good ones with no hassle.
Bear in mind that I was not trying to enlarge the thing, only to polish and smooth it. When I was lapping the .257 mould I used 3-4 bullets as laps and I only used one for each cavity with the RCBS. I would be shocked if I removed more than one or two tenths off the diameter.
First off, I center punched the base of the lapping bullets with a automatic punch which made it easy to get it close to the center. Next I drilled a .150 hole about a quarter inch deep in each bullet with a 1/4” drill motor and started a wood screw in the hole. Dabbed a little 320 grit valve grinding compound in the cavities, put the bullets in and put the whole thing in my little precison vise. I carefully closed the vise while turning the bullets, one after the other with a screw driver.
I tried to keep the pressure light enough that I didn't run the screw in any deeper and expand the lap. It took about fifteen minutes of turning the laps and tightening and loosening the vice until I got the vice shut tight. I took the blocks apart and wiped the excess lapping compound off the faces of the moulds and continued again until I could close the vice tightly. One cavity cleaned up a little more than the other but I generally segregate bullets by cavity so I wasn't to concerned with that.
The good vice made it a lot easier but I don't think it would be any problem to use a bench vice or even the handles themselves. I made that vice myself, to brag just a little.
I don't believe in fixing things that aren't broken and my wife might say I don't fix half the stuff around here that is broken. However; if you have an obstinate mould I would sure recommend giving this a try.
Thanks for reading
Ken