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Very Hot Topic (More than 25 Replies) Enlarging bullet mould cavity (Read 2333 times)
silver
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Enlarging bullet mould cavity
Jun 15th, 2019 at 11:45am
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I read several years ago on castbullets.com about enlarging
The cavity by lapping the cavity of a mould with lapping
Compound and a casting from said mould to inlarge it. I have a 2
Cavity steel Lyman mould I would like to inlarge 1 of the cavities from .321 to .324 to see if it will work better for a 32-40 I have.
Has anyone on here ever tried it? And what might drawbacks be?
Any feedback would be appreciated .

Thanks doug
  
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JLouis
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Re: Enlarging bullet mould cavity
Reply #1 - Jun 15th, 2019 at 12:18pm
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Often times depending on the bullet design it's allot easier, more precise and in keeping it round by just boring out the baseband. I have done this several times for friends using a four jaw chuck, guage pins, mini carbide boring bar and dial indictors to track movements. Also need to increase the size to allow for the shrinkage to achieve the finished size that you are actually wanting to achieve. Might sound a bit challenging but it is actually not all that difficult to do if you happen to have or know someone who has a lathe. Based on the increase in size from what you have described that is quite a bit of lapping for one to try doing without creating undue damage to the mould and especially in regards to the grease grooves and more importantly maintaining the bullets roundness.
  
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uscra112
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Re: Enlarging bullet mould cavity
Reply #2 - Jun 15th, 2019 at 12:59pm
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Certainly possible.† Has been done many, many times, including twice by me.

Assume when you say "steel" mould, you actually mean cast iron.† Cast iron laps easily, steel does not.† The difference is that cast iron is a friable material, from which tiny fragments can be removed with low energy of dissociation.†

Only "tips" I have to offer are 1.) Drill a small hole in your lap, (on center of course), and press in a Torx bit to use as the driver.† The old recommendation of using a screw doesn't really work all that well, since you should be reversing the direction of rotation frequently.† †And 2.) Don't use a lot of lapping compound.† Spread a little bit on a flat surface, roll the lap in it using another flat object, using some pressure, so as to impregnate the lap with grit. Gently rinse the lap in solvent to remove excess before going to work.

Oh, and don't turn the lap fast.  A power screwdriver is OK, your electric drill is not.  Use a very long extension to avoid putting side thrust on the lap and thereby making your cavity oval.
« Last Edit: Jun 15th, 2019 at 1:04pm by uscra112 »  
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silver
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Re: Enlarging bullet mould cavity
Reply #3 - Jun 15th, 2019 at 1:21pm
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The mould is iron, I like the bit idea instead of the screw.
Mr. Louis, unfortunately I or nobody I know owns a machinist lathe.im woodworker and do have a drillpress.

Thanks doug
  
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OLD TUCK
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Re: Enlarging bullet mould cavity
Reply #4 - Jun 15th, 2019 at 4:45pm
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Doug, the boring in a Metal Lathe is the way to go. I am sure if you poke around the folks you know you will find a Machinist guy who has a 9" South Bend with a four Jaw chuck. The only Boring you should have him attempt
is the Base Band. I have some number of "JUNK" molds that represent my efforts to go into the Mold and make changes in either the Nose Shape or inner diameter. Finally figured that was not going to work in a Manual lathe.
What you should do is cast a small quantity with your Alloy and measure them
up and Pin Gage the Base band diameter in the Mold. Knowing what they Measure as cast and knowing what the Base band measures gives you a close figure for shrinkage. Now you can decide what you think the Base band diameter should be and bore accordingly. This process has worked very well for me for
30 Years or more and I have been able to hand back bullet Molds that then cast very good bullets that shoot well. HTH FITZ. OLD TUCK Smiley
  
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marlinguy
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Re: Enlarging bullet mould cavity
Reply #5 - Jun 15th, 2019 at 7:52pm
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I've lapped molds on the base band using valve lapping compound. I simply drilled a center hole, and then threaded it for 10-24NC thread. Screwed in a screw with a jam nut against the bullet base. Then chuck it in a drill motor and put lapping compound on the base band, and oiled the upper bands. spin the bullet in my drill press and close the mold around the bullet as it spins.
It goes fairly well, so don't polish too long without checking it. I've opened them up a couple thousandths, but as JLouis mentioned it's better to use a lathe if you're going very far, or risk getting out of round. He did a Saeco for my Hepburn, and it's the cat's meow!
  

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George Babits
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Re: Enlarging bullet mould cavity
Reply #6 - Jun 15th, 2019 at 8:59pm
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I have to agree with Doug (OP).  Everyone on this site doesn't have a machine shop at his disposal for this sort of thing.  I for one certainly don't.   If I wanted to open up a mould a few thousands I would cast a bullet of wheelweights or #2 alloy, drill a holl in a slug, put a small torex screw into it and give it a try.  If it works, great.  If it doesn't you still have the other cavity to work with.   I once lapped a 58 muzzle loader with a hard cast minie attached to a ramrod with a screw and using valve grinding compound.  Worked great.  Later when I traded that musket off the fellow who got it was winning all sorts of matches with it.  Having a complete machine shop is great, but the reality is that most everyday shooters don't have one.

Keep your powder dry!
George
  
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Re: Enlarging bullet mould cavity
Reply #7 - Jun 15th, 2019 at 10:43pm
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I've opened several RB molds by lapping. A harder bullet is better to use because the thread will be stronger for the screw used.

Do not use much lapping compound, if it gets between the blocks, it holds them open and you get a out of round mold that way. Do everything you can to keep the compond of the blocks.

Frank
  

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Re: Enlarging bullet mould cavity
Reply #8 - Jun 16th, 2019 at 8:54am
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Enlarging bullet mould cavities can be done by lapping with succeedingly larger castings, but in my experience, there is a law of diminishing returns that says +0.001Ē is easy; +0.002Ē is doable, but laborious; +0.003Ē is at or beyond the outer limit of possibility.† Trying for that much or more may eventually get you your desired dimension, but the bullet cavity will become noticeably oval across the casting line.

A regular production mould is likely somewhat oval already, so this condition may or may not be bothersome to the end user, who sizes the bullets in a lubrisizer.† Those who insist on zero runout may get more upset if their expensive custom mould is a half-thousandths fatter across the parting line at the end of a lapping session.

Lapping ovalizes bullet cavities faster per thousandth diameter increase if the mould is held tightly in handles, but some runout will occur even if the blocks are fixtured in a four-jaw lathe chuck, and the excess lapping compound and swarf cleaned off the faces frequently.

I usually put the bullet in a collet, drill and tap it with some appropriate-sized tap, and leave the tap in the lead as the shank.† If I use an electric drill, it is a variable speed one, at very low rpm.† Thirty seconds or a minute slow turning, open blocks and clean faces, the same time more in reverse, clean mould and cast a few to check diameter, and, if necessary, supply the next size laps.† It is, of course, more involved with the four-jaw chuck, but the buildup must not be allowed.
« Last Edit: Jun 17th, 2019 at 9:22am by Bent_Ramrod »  
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JLouis
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Re: Enlarging bullet mould cavity
Reply #9 - Jun 16th, 2019 at 11:50am
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Well put and you are correct Bent_Ramrod the first thing to go is the roundness and the more you lap the worst.it gets. More times than not the bullet being used for the lap isn't round to start out with. Also when the item being used to turn the lap is inserted into the bullet being used for the lap it will expand it. If that item is not now centered in the lap it will create out of roundness to the lap. So lets say one has now been able to get all of this correctly accomplished and it's time to start lapping. Now one has to turn this lap while maintaining zero runout to the item being used to turn the lap so it does not induce any additional out of roundness as well. Increasing the size of the bullet can be done those are just a few of the challenges to think about before taking on the task. And when you include the hand pressure while closing the mould requiring it to be equally applied to each side of the lap. Well it too can add to the difficulty of trying to keep the mould cavity perfectly round as you continue to take more material off as Bent_Ramrod has correctly stated in his post.
  
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silver
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Re: Enlarging bullet mould cavity
Reply #10 - Jun 16th, 2019 at 2:49pm
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Update;
Gave it a try the 2 cavity mould was already 4 thousands out of round , lapped it , I did get it to .324 one way but now it is
6 thousands out of round. Oh well live and learn. I still have the other cavity that is only used for a lever gun I do not shoot much.
Now I need to do a chamber cast to see how large of a bullet I can fit in this chamber. Because when I slug the bore I come up with
.326. standards say I should shoot .327 , don't know if that will chamber . Another thing is to try 30-1 instead of 20-1 for more bump up. It's an all original 441/2 Stevens in near perfect condition. I would just like it be able to shoot  1 to1 1/2" moa. It will not be used for any competition.
Well on to the next step.
Thanks for all the feed back

Doug
  
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JS47
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Re: Enlarging bullet mould cavity
Reply #11 - Jun 17th, 2019 at 12:39am
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This thread brings up a couple of thoughts.

1. I've heard of opening up a mold by using some thin tape between the blocks. I think it's called "beagleing"? which leads to thought number 2:

If a bullet is out of round the same amount on opposite sides is it also out of balance?

JS
  

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uscra112
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Re: Enlarging bullet mould cavity
Reply #12 - Jun 17th, 2019 at 12:55am
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Silver, how are you measuring roundness.?† Those numbers sound absurdly bad to me.†

And .326 sounds awfully big for a .32-40 barrel, even for Stevens.† Are you using a micrometer or a caliper?† Is it properly calibrated?

n.b. I lapped an aluminum Lee Bator mould from .225 to .228+ to get bullets for a .22-20 project.  I just took an as-cast bullet from storage; it measures less than .001" out of round, using my best 1" micrometer.   What did I do wrong?
« Last Edit: Jun 17th, 2019 at 1:17am by uscra112 »  
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silver
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Re: Enlarging bullet mould cavity
Reply #13 - Jun 17th, 2019 at 9:04am
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Measured bullets that were cast from mold before and after
Lapping with micrometer on both seam and non seamed sides.
I also bought a #62632 saeco mould awhile back and that mould is 7 thousands out of round from factory. (Money out the window).
Unfortunately I don't have deep pockets to keep buying molds.
So I'm might just try a .324 from accurate with 30-1 see what happens.

Thanks doug
  
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Bent_Ramrod
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Re: Enlarging bullet mould cavity
Reply #14 - Jun 17th, 2019 at 9:48am
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Iíve never lapped an aluminum mould, just the iron alloys.  Aluminum may be more forgiving, since it would obviously cut easier and faster.  It would be interesting to know how big an aluminum mould cavity could be lapped to before it started going oval.  I would think it would eventually.

If you have a good sizing die that swages the bullet shank round, there may not be any indication of a problem in the actual shooting results.  If castings from a custom mould are pan-lubed, the bullet will remain oval, but of course will round itself quickly enough when it goes through the leade and barrel.

There was a fanciful discussion in one of the old American Rifleman magazines about how sizing and shooting couldnít help out-of-round bullets that much because the noses and the bottoms of the grooves would still be oval.

I havenít noticed any effect from out-of-roundness in my shooting of all kinds of bullets from all kinds of used and abused (and reconditioned) moulds purchased at gun shows, but Iím not all that great of a shot.  The smallest five-shot group, with whatever components, is The Load, as far as Iím concerned.  With me as the big variable, I at least have the luxury of not having to flip out over such tiny nuances.
  
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