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Gone Fly Fishing
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Bullet Mould Lapping ?
Oct 13th, 2010 at 7:57am
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  I've read several articles, one in the Single Shot Exchange magazine which explained the process of lapping a bullet mould in order to achieve a larger diameter casting.

What can one expect as regards to the additional size that can be obtained from lapping ?  Is .002" do-able ?  What would be the best medium/grit to use when lapping an iron block mould ?  Any cautions and/or insight you can offer from your own experience ?

   Creedmoormatch
« Last Edit: Oct 13th, 2010 at 8:04am by Gone Fly Fishing »  
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zeke
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Re: Bullet Mould Lapping ?
Reply #1 - Oct 13th, 2010 at 10:47am
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     Hi Creedmoor:

     Your question about lapping a bullet mold is quite interesting to me.

     I have been taught that lapping is a process that is designed to remove very little material.  I am under the impression that tool marks, very precise fits etc. where very little material is to be removed is in the realm of lapping.

      I have heard of people removing rust from bullet molds by lapping, but they never have said how deep the rust was.  Your idea as to remove .002" seems like more than can be removed by lapping.

      Perhaps if one used a very coarse "lapping" compound one could remove this much metal.  I have seen a person drill and tap a bullet that has been cast in the same mold and thread a rod into a tapped hole and use a power source to "lap" the mold to improve the finish of the bullet.  This was a fix for a rough mold. You are talking about .001" removed from each side of the mold may be doable via the  above method.  It may work.  What do you have to lose but some time.

       Good luck and keep us posted.
                                                                      Zeke Smiley
  
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digitall423
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Re: Bullet Mould Lapping ?
Reply #2 - Oct 14th, 2010 at 7:33am
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I've got the same problem Webb. My son and I both use a Paul Jones mould that, if you use a little imagination, is only about .0004 larger than the groove diameter of our barrels. I definitely think it is possible to remove .100 or so quite easily. In fact I think the hard part will be warming the mould up to casting temperature then letting the bullet cool so it can be measured. My plan is to only enlarge the base band.
  
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JLouis
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Re: Bullet Mould Lapping ?
Reply #3 - Oct 14th, 2010 at 9:23pm
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The hardest part of lapping a mould is insuring that the bullet is perfectly round within human limitations of around .0005 - .001

Taking off the material in order to enlarge the diameter is relatively easy using the scope ring lapping compound.

J.Louis
  
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Re: Bullet Mould Lapping ?
Reply #4 - Oct 16th, 2010 at 7:25am
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Quote:
insuring that the bullet is perfectly round within human limitations of around .0005 - .001
J.Louis


I am wondering if a mould that left the manufacturer "out-of-round" could be made perfectly round within human limitations by the means of hand lapping ?  Or would, "once out of round, always out of round" apply ?


  Creedmoormatch

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« Last Edit: Oct 16th, 2010 at 8:20am by Gone Fly Fishing »  
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Green_Frog
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Re: Bullet Mould Lapping ?
Reply #5 - Oct 16th, 2010 at 8:13am
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CMM,

     Logically, lapping the mould should improve its roundness... I'm not sure to what degree, but it stands to reason that the most contact would be between the largest diameter of the bullet and the smallest diameter of the mould, so they should begin to work hardest on each other.  That said, I agree with the other posters who have said that you should not expect a significant dimensional change from lapping... at best you will probably just polish out minor surface irregularities with normal lapping action.  The preceding comes from extensive reading and conversation but only limited actual experience with a couple of moulds.  YMMV, but I doubt it!  Wink

Froggie
  
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MikeT
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Re: Bullet Mould Lapping ?
Reply #6 - Oct 16th, 2010 at 7:58pm
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If you want to take a few thousands off the interior of a bullet mould, use valve grinding compound.  Be carefull how long you turn the bullet in the mould as it takes alot off in the short time.
I have only done this on a PP bullet mould, so I do not know what kind of issues may arise with GG bullet moulds.

Keep on hav'n fun!
MikeT
  
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Re: Bullet Mould Lapping ?
Reply #7 - Oct 16th, 2010 at 11:00pm
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MikeT,

What grit size did you use?
  
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Re: Bullet Mould Lapping ?
Reply #8 - Oct 17th, 2010 at 3:29am
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A couple weeks ago I lapped this mold .001 bigger in about thirty minutes.  .395 to .396.

I use a hardwood lap in the lathe. Cant remember what grit compound I used. 

                Joe.    Smiley
  
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Re: Bullet Mould Lapping ?
Reply #9 - Oct 17th, 2010 at 6:03am
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There's a l0ot about lapping molds here, in chapter 4.0 in FILES.

(You need to Login or Register to view media files and links)

joe b.
  
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Re: Bullet Mould Lapping ?
Reply #10 - Oct 17th, 2010 at 6:13pm
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BP,

The grit seems fairly course.  I just went to the NAPA store and picked up whatever it was that was valve grinding compound.  They only had one type as far as I know.

Keep on hav'n fun!
MikeT
  
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Re: Bullet Mould Lapping ?
Reply #11 - Oct 17th, 2010 at 9:59pm
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MikeT,

Thanks! I'll drop by NAPA and take a look. 
  
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