Mould lapping

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  • Last Post 17 September 2009
KenK posted this 14 August 2009

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.

http://www.castbulletassoc.org/view_topic.php?id=4590&forum_id=10>http://www.castbulletassoc.org/viewtopic.php?id=4590&forumid=10

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

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chboats posted this 14 August 2009

Ken  - Great looking moulds!! I have tried lapping moulds sometimes with success and sometimes not. The trouble I had was they ended up more out of round. The only way I could get them round was, as you said, make sure the mould faces were free of grinding compound and clamp them in a vise with enough presure to make the mould halves are tightly mated. A trick that I would like to pass along is I drill a hole in the bullet like you did but instead of using a screw, that you can only turn in one direction, I tap a torx bit into the hole. I use a number 15 for a 30 cal bullet. It is strong enough in the lead to turn the bullet but don't put too much torque on it or the hole will strip. Being the lazy person I am, I also used an electric screw driver.

Carl

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hunterspistol posted this 20 August 2009

   This is some excellent information.  Thanks KenK.

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GL49 posted this 20 August 2009

the torx bit idea sounds like it makes a nasty job easy. I'm going to have to try that with one of my Lee molds. Do you think the aluminum molds would require a finer grit of grinding compound?

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KenK posted this 28 August 2009

I picked up a couple of Torx bits this week and just finished lapping a mould using them.  They work much better than the wood screw.

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Seabee posted this 15 September 2009

Using my lee mold my bullets come out just under the 452. like 451. my sizer is 452 but under sizes by .001 so it is the same size for most of the bullets. My lube keeps seeping out. Will lapping fix this?  I  think part of the issue is I use the spray on mold release. It builds up and has to make the bullets smaller. They just do like to drop out like they do with the spray.. I need to try the match method.

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KenK posted this 15 September 2009

It shouldn't be too tough to lap a thousandth out of an aluminum mould but I think the more you take out the more you are going to get it out of round.

I have to say though; you seem to be a “go big or go home” kind of guy so maybe you should just go ahead and buy a nice H&G or Ballisti cast gang mould and be done with it.

 

 

 

 

 

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lordgroom posted this 15 September 2009

On another forum I saw someone place a nut on top of the mold (not on the sprue plate).  The poster then poured a bullet through the nut making sure the lead filled the nut too.  Then he was able to turn the bullet with a socket driver.

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JetMech posted this 16 September 2009

That's a slick idea. I think the nut would have to be fairly large, otherwise you would just twist it off. You would just have to be carefull not to scar the top of the mold, but that could be lapped out also. Which brings up another subject: how to lap flat surfaces.

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ubetcha posted this 16 September 2009

I tried using the nut way to lap and all the  nut did was float on top of the lead when the cavity was full and then cock of to the side a little just as the lead hardened.

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JetMech posted this 17 September 2009

I've been thinking about how I would go about it. I think a large nut with an inside diameter that is just under bullet diameter would be the way to go. Put a piece of .002 aluminum shim stock in between the nut and the mold, clamp the shim/nut to the mold, poke a hole in the shim and pour the lead until you get a sprue on top of the nut. Remove the bullet/shim/nut and tear away the aluminum shim. That way you have a .002 clearance between the nut and the top of the mold.

Or you could just go with Ken's method. Life is good.:coffee

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KenK posted this 17 September 2009

Dollar Bill wrote: Or you could just go with Ken's method. Life is good.:coffee

The wood screw really does work quite well.  Drilling the hole is no problem at all, even with a simple hand drill.

I think some shorter hex head screws would work much better than the ones I was using.

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JetMech posted this 17 September 2009

KenK wrote: I think some shorter hex head screws would work much better than the ones I was using. Internal wrenching screws (Allen wrench) would also work. One thing I think you want to avoid is putting downward pressure on the screw as you rotate it so as not to change the lube groove dimensions, except for OD.

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