Need to make mould cavities a tiny bit bigger...

[mattw]

I just acquired a mould here that casts a tiny bit small in all of my alloys. It is an older Lyman 358xxx 2C, is not common and is in great shape, but I am getting drops around .357-.3575 and gas checks do not get tight on the shanks. I could beagle the mould and drop bigger, but out of round bullets. This is really not the route I wan to go. I need to gain .0015 to .002 to reach the diameter I am looking for. I really would like to be .359+ on the as cast diameter.

So, I am considering this process, please tell me if I am nuts.
1) cast a few out of lino for hardness, or water quench a few with my 94/3/3 alloy
2) size to .357 or there about with no lube
3) drill small hole in base and run a small screw in tight
4) coat the bullet with Clover valve grinding compound
5) spin a few times with screwdriver
6) cast a handful of test bullets to measure
7) start with new bullet and repeat until diameter is where it needs to be

This is a very long bullet, with no danger of the screw exiting the end of the bullet. After the desired diameter is reached, I would cold blue the cavities to prevent rusting and help drop out. Or, would casting a bit cause the cavities to blue in?

245723

Thanks Matt

[sundog]

If it were me..., I would powder coat some first and see what happens.

[mattw]

If it were me..., I would powder coat some first and see what happens.

I have and they shoot great! I am making them for my old Marlin 1894C and sometimes for 38 Special with a very heavy bullet. When PC'ed they will shoot cutting at 20 yards, about all my eyes are good for offhand anymore. I did PC them once and shot them and I also tried with a second coat after the GC was installed. The second coat was about right, coats were very thin as the humidity is a beast her at this time of the year and I do not have humidity controls where I cast.

[country gent]

Lapping the mould ( the process you described) will gain what you want.
Its more tedious to do than hard. It needs to be done right and with care.

Tools you will need are simple hand tools
Small tee tap handle
a small vise or square clamp
Ink marker or lay out fluid

Basic materials you will need
1/8" key stock
600-800 grit lapping compound
2 flat steel plates, 1/4" X 1" X 4-6"
solvent

Cast several bullets from each cavity these need to be food but a normal alloy is fine
spot bases center thru sprue plate
Drill for 1/8" key stock to just fit.
epoxy a piece of key in the hole 1 1/2" long. make 3-4
Lightly coat one plate with compound roll bullet between the 2 plates to impregnate the bullets
Mount in the tap handle and insert gently and carefully into blocks.
hold closed in vise or clamp lightly
With a tapping type motion rotate lap back and forth roughly 1/4 turn 3-4 times rotate and repeat thru 2 rotations.
Clean and check size by casting with the desired alloy
repeat as needed to get to size.
inking the cavity will show the clean up and how round the cavities are. This process will true up and adjust a moulds size. But you cant cut it smaller so go slow and check often. A light polish with a fresh lapp and simichrome flitz or tooth paste fives a very fine polish. Keep in mind lapping a hole is 2 for 1 for every .001 removed dia changes by .002. So your talking .0075-.001 on a side is all.

[Conditor22]

http://castboolits.gunloads.com/showthread.php?32584-Leementing-Documentation-w-Photos

Different PC's will add different diameters to the boolit

[masscaster]

Water quenching will help maintain a larger diameter boolit as long as there is antimony in the mix, provided they are dropped into the water fairly quickly.

[mattw]

http://castboolits.gunloads.com/showthread.php?32584-Leementing-Documentation-w-Photos

Different PC's will add different diameters to the boolit

I know, but the PC coat is a bandaid for a mould that really should drop bigger. I do not PC everything, nor do I want to.

[oldhenry]

I know, but the PC coat is a bandaid for a mould that really should drop bigger. I do not PC everything, nor do I want to.

I don't PC either (nothing wrong with it......I just don't do it). Since you don't PC, it looks like Country Gent outlined (very well) the course you need to take. Don't get in a hurry & good luck.

Henry

[mattw]

I don't PC either (nothing wrong with it......I just don't do it). Since you don't PC, it looks like Country Gent outlined (very well) the course you need to take. Don't get in a hurry & good luck.

Henry

I do PC, but mainly for pistol bullets. I really love the performance in pistols from 22TCM up to 45ACP and 41mag. I just do not see the improvement in rifles, other than they are easier to clean... sometimes. These do indeed get to the right diameter with PC, but I would really like to lube with Carnuba Red for this rifle. I do like it PC'ed in a 38 special revolver, less smoke and really clean barrel.

Plus, I really want to fix it properly. That way I do not have to remember that it always needs a coat of PC, then the gas check and then maybe another coat of PC.

[Bent Ramrod]

I would not size the castings for lapping. Use them as-cast.

I drill the hole in the base such that a small (8 or 10) tap can be run in until it bottoms out. The tap is used as the shank to spin the lap on.

I put the blocks in handles, squeeze the handles lightly with the charged casting in the blocks, and spin the lap very slowly in a variable speed, reversible drill in my other hand. After a couple spins, the Clover compound and lead swarf squeezes out, and I stop the process, wipe it off the block faces, put lap back in the cavity, squeeze a little tighter, and spin slowly again a couple turns. I clean the faces again.

I continue this routine until I can squeeze the handles as tightly as when I am casting while the lap is spinning. Then I give it about 30 seconds at ~60 rpm forward, open and wipe faces, and 30 seconds of 60 rpm in reverse. I clean the blocks, put the lap in the vise, reverse the drill to get the tap out, and cast a few boolits to check the diameter increase. I repeat as needed with the larger castings until the desired diameter is obtained.

I can only get around 0.002” before the cavity starts getting oval, but most of the cavities I’ve lapped are in production moulds that were somewhat out of round to begin with. The cavity will need breaking in (oxidation or heat bluing) before really good boolits come out, but they don’t have to be perfect to be useful for lapping.

I’ve only lapped single-cavity iron moulds this way, but I’ve been pretty happy with the results.

[GhostHawk]

Watch out you get NO compound where the gas check shank is or forward of the lube grooves.

With that caveat, I have done it and had good luck doing so.
Only I used a nut that fit my 5/16ths nut driver, did not use the sprue cutter, poured the lead down the nut hole. I suspect the screw is the better option.

Did not take much or long and my mold was casting 2 to 2.5 thousandths fatter which was what I needed.

[Larry Gibson]

Why not just change alloys?

[JonB_in_Glencoe]

If I were to want to lap the mold cavities of an iron mold, to increase the boolit's diameter. I'd use the WEET method. That way you only enlarge the portion of the boolit that you want enlarged.

http://castboolits.gunloads.com/showthread.php?257858-Expanding-a-boolit-mould-the-quot-WEET-quot-method-(In-parts)

[trapper9260]

I was wonder about how to go about doing this till I see this post. Now I know how to thank you .

[trapper9260]

If I were to want to lap the mold cavities of an iron mold, to increase the boolit's diameter. I'd use the WEET method. That way you only enlarge the portion of the boolit that you want enlarged.

http://castboolits.gunloads.com/showthread.php?257858-Expanding-a-boolit-mould-the-quot-WEET-quot-method-(In-parts)

I will need to check that link out also. I know if you go with a different alloy that I can get some bigger boolits. I do not PC just normal lube and size.

[mattw]

Why not just change alloys?

Larry, I have tried with 94/4/4 as cast and water dropped and COWW (old stock) + 2% pewter. Both are to small, not much... but enough that gas checks do not get tight in a .358 size die and small enough that lube flows from the small groove above the check up to the main lube grove. My Marlin is an old microgroove that needs to be at least .359. I did make some fit with PC and they shot very well, but the ones that are to small with conventional lube opened way up at 50 yards.

I will try the above procedure, have looked for this mould for a long time and the mould itself is in great shape, just small.

[rintinglen]

If I were to want to lap the mold cavities of an iron mold, to increase the boolit's diameter. I'd use the WEET method. That way you only enlarge the portion of the boolit that you want enlarged.

http://castboolits.gunloads.com/showthread.php?257858-Expanding-a-boolit-mould-the-quot-WEET-quot-method-(In-parts)

What he said. Mr WEET made a wonderful series of posts precisely explaining his method of uniforming and enlarging undersized boolit cavities. For a minor increase in size--it is the way to fly.

[RED BEAR]

Lapping the mould ( the process you described) will gain what you want.
Its more tedious to do than hard. It needs to be done right and with care.

Tools you will need are simple hand tools
Small tee tap handle
a small vise or square clamp
Ink marker or lay out fluid

Basic materials you will need
1/8" key stock
600-800 grit lapping compound
2 flat steel plates, 1/4" X 1" X 4-6"
solvent

Cast several bullets from each cavity these need to be food but a normal alloy is fine
spot bases center thru sprue plate
Drill for 1/8" key stock to just fit.
epoxy a piece of key in the hole 1 1/2" long. make 3-4
Lightly coat one plate with compound roll bullet between the 2 plates to impregnate the bullets
Mount in the tap handle and insert gently and carefully into blocks.
hold closed in vise or clamp lightly
With a tapping type motion rotate lap back and forth roughly 1/4 turn 3-4 times rotate and repeat thru 2 rotations.
Clean and check size by casting with the desired alloy
repeat as needed to get to size.
inking the cavity will show the clean up and how round the cavities are. This process will true up and adjust a moulds size. But you cant cut it smaller so go slow and check often. A light polish with a fresh lapp and simichrome flitz or tooth paste fives a very fine polish. Keep in mind lapping a hole is 2 for 1 for every .001 removed dia changes by .002. So your talking .0075-.001 on a side is all.

+1 for this only thing i will add is be patient and as said check often.

[popper]

Beagle first and see how bad they shoot. Surprize!? It's a steel mould and you are in for a lot of work! 357, not 308W so you aren't pushing it too hard.

[mattw]

Ok, so I now have the mould basically fixed. I used the WEET method. I did chicken out and put it together to make some test casts, now dropping at between .3595 and .360. Gas checks are fitting better as well. I have not polished the cavities yet and will do that and should gain the last .0005 that I want. This mould is the 358627, so 215 gr. 38 SWC. I did not lap the driving band in front of the front crimp groove and I did not lap the nose, did not want either to change size. The cavities are smoother now than they were before and bullets drop better. I used Clover 1A valve grinding compound, must have been 70 years old but it was still good.

Now, do I cold blue the cavities or do I just cast until they heat color?

Had to try them out... 3.5 of Unique in a 38 Special case seated to the top crimp groove netted me 698fps average and 233 ft-lbs of energy. They are shooting better than I can shoot at 20 yards with an old S&W 15-3 and open sights. I also shot a few of the same load in my Marlin 1894 microgroove and cloverleafed them at the same 20 yards with open sights. The velocity went up to an average of 856 in the rifle. I am going to have to try a few of them from the bench this summer. I was able to ring my 100 yard plates a few times with the rifle as well. No leading, that Marlin with the microgroove will lead with a smaller than should be bullet. Now I have the option of PC'ing or conventional lubing my bullets.

I also took the time to lap in a thick sprue plate for the mould and cold blued the nice smooth surface. I lapped for the better part of 30 minutes with the 1A Clover on glass and still could see machine marks, I will go back at another time and work on the plate more. Lyman's replacement plates really are not very good, but plenty of metal to work with.

[country gent]

Ideally when lapping you want the lap to be the softer material. This way the compound impregnates the lapp and cuts the material. A very simple flat lap can be made with 2 lengths of clear 2X4. sand them all flat on one surface with your glass. They are now very close to flat. Mark 1 edge 1 2 3 each on 1 board you want a #1 #2 and #3 board. with number 1 facing sand #2 and #3 facing then 1-3 with numbers apart and 2 to 3 with numbers apart The 2 to 3 numbers together and 1 to 3 numbers together. Put light pencil lines across working surfaces to see when they are cleaned up. Here a coarser paper 180 -220 is better as it cuts cleaner and faster and leaves a rougher surface to hold the compound. This will cut the steel quicker and truer. Even just off the glass it ight be good enough.
Most of the old cast iron and brass lapping plates had a line pattern in squares or diamonds cut in them to help hold compound and oil. These plates would cut fast and true When lapping on one a figure 8 pattern was used sliding from side to side and top to bottom utilizing as much of the plate as possible, this helped to keep the plate flat also.

with your makeshift wood plate use it right after dressing down so moisture changes don't affect it. Use an oil based compound and light oil to lubricate it. Last is rotate and use as much of the surface as you can working in the figure 8 pattern. Valve grinding compound is coarser than the "graded" versions and is expected to break down in use getting finer as its used

For a surface polish one of te clean blocks with flitz or toothpaste will really shine it up. Or rub some jewelers rouge in it

[mattw]

Thanks, would not have thought of using wood! I have a couple of plates of aluminum that I have thought about scoring with a file and using. Would they be just as good? If cared for I suspect that I could use them over and over.

[country gent]

Aluminum will work finish down by the above rule of 3 with your lapping compound instead of sand paper. Once flattened the aluminum wont change with moisture but may due to stress and heat, but this will be a very small change.