Expanding mold cavities

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  • Last Post 19 February 2015
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R. Dupraz posted this 23 January 2015

I found this method for lapping out mold cavities on the Cast Boolet forum the other day and thought some may be interested.       In the past, I have “Beagled and used the labor intensive cast and lap method to enlarge mold cavities in order to get the intended diameter. While both work, I was never really satisfied with either.         With the “week” method, you only need to cast a few bullets at the beginning and can then measure the amount of enlargement as you continue to lap the cavities in order to get the diameter that you want. No cast, cool, lap, heat and cast new laps. I tried this a couple of days ago to enlarge a double cavity 246 grn 44 cal SWC mold and it worked perfectly.      Expanding a Boolet Mould The “Weet Method"  By saxguy Cast Boolet forum  

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gpidaho posted this 23 January 2015

Mr. Dupraz: Thanks for pointing out that Sticky as I hadn't read that one. I think that is a very well thought out method for mould enlargement. Instructions are very easy to follow as presented by the author. He makes a PITA project a lot less time consuming. What folks are willing to share on these forums sure do add to my enjoyment of this hobby. Thanks to all GP

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delmarskid1 posted this 24 January 2015

I LIKE IT! I LIKE IT A LOT! The part about not making new slugs to lap with ten times really appeals to me

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R. Dupraz posted this 24 January 2015

you're very welcome Gents. Happy to pass it on. Especially when I find something that works as advertised. And after trying this method on that mold, I can assure you that it does. So happens that I found this at an opportune time as I needed to enlarge a mold for my Ruger 44 special.         I did change one thing though. Instead of rolling the bullet between two files to create stipling to hold the compound and then pressing down on the mold to embed the compound, I spread the lapping compound on a piece of glass plate. And then with a length of steel flat, rolled the bullet through the compound by sandwiching the bullet between the glass and steel flat until the driving bands were loaded with the lapping compound. Then with a tooth brush, cleaned all the loose compound off the bullet before I put it in the cavity of the mold. This results in  the driving bands being already loaded. No pressing down on the mold to load the bands and simplifies the lapping because there is much less compound that gets between the face of the blocks and then has to be cleaned off. I used a 3/8 variable speed electric drill.       One more thing. I noticed that this method tends to cure any out of roundness in the cavities as well. That target  was shot with the lapped out mold. Cured my forcing cone leading problem and shoots pretty good as well first time out. Five shots at twenty yds. RCBS 246-SWC

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RicinYakima posted this 24 January 2015

Can someone post a link that works? Thanks, Ric

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RicinYakima posted this 24 January 2015

Good methodology, and should work just fine. I think I will try it the next time I need to increase the diameter of a bullet mould cavity. Thanks for the link, .41 mag, for the post, RD.

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tlkeizer posted this 26 January 2015

Greetings R. Dupraz,   Nice Group.   TK

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R. Dupraz posted this 26 January 2015

Hey Terry:   We have had some of your temps down here on the Great Plains recently but they have turned around a little lately so it's not too bad.    Those last five shot groups with the Ruger were the best ever since the gun was new out of the box. I thought that I had measured things accurately at first and thought I was in good shape. But after I fire lapped the thread crush out, the groups opened up and I was getting some leading in the forcing cone. Kinda disappointed and scratching my head.   So, I checked the diameter of the throats and bullet again. Horror of horrors!. The bullet was too small. Either my first measurements were wrong or I also lapped the throats along with the thread crush. Which was a worry at the time. At any rate, the now throats measure .432” and my bullet was at .430"+. A no brainer. I then lapped the mold out to .431"+ using the “weeks” method and tried again.   The above group illustrates the results and the forcing cone leading was no more. So, considering the shooter, I think that's good enough for this poor knave.

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.22-10-45 posted this 29 January 2015

I was working on an old Lyman .38 wadcutter mould..on top surface of mould..metal was dented inward..right on cavity parting line..how to remove offending metal without scratching or buggering up base band? I tried increasing diameters of gage pins until I found a snug fit. This next step is important..using a hone carefully round edge of pin so as not to gig in or scratch..I used a bench lathe..though a drill press or even hand drill would work. I then carefully brought blocks together in a milling machine vice. A little polishing and defect was gone! Another problem arose when I began casting..cavities dropping about .001” too small. Back to the gage pins...next size up wouldn't fit..again edge rounded & blocks carefully closed. This did the trick..base band expanded. Now there probably is a limit to how much you can increase without distorting metal..but for 1 or 2 thou..and especially for dent removal those hardened pins are nice!

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John Alexander posted this 19 February 2015

I was impressed with the tutorial by Mr. Weet on the Weet method.  Thanks RD for putting us onto it.  For the most part the method is similar to what I have done in the past.  The part that was different and of most interest to me was how to use swaged bullets to judge the progress of the lapping.  That would obviously save a heck of a lot of time over the lap and cast, lap and cast, lap and cast method that I have been using.

I have a bore riding type bullet mold that I want to enlarge the nose a bit for a better fit without enlarging the rest of the bullet. I have successfully lapped out portions of bullets before so know how do that -- not so sure about the swaging.

I thought the first order of business would be to assure myself that I could do the swaging and get consistent measurements on the swaged bullet or bullet nose.  After several tries I haven't been able to do that.  In spite of trying to use the hammer consistently the slugs so far  have varied by over .002".  Since I only want to remove only .0005” that obviously isn't good enough and I need advice.  I have been using just the nose part of bullets cast of lead that Brownells sells as 99.9 % pure (very soft.) I have been using a .18” punch (the biggest I happened to have) for the .219” nose cavity and a small ball peen hammer.

Any and all advice will be appreciated. John

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