Honing out a mold to increase bullet diameter

[LawrenceA]

I have been casting for a few years and have a collection of maybe a dozen molds but I am still a very basic caster.
I recently purchased a Lyman Gould mold for my 45-70. The bullets drop at around 456 to 457. I have tried using a hot mold and cooler lead. I have also tried powder coating a couple of times to try and bring the diameter up to 459 but they still come up a bit looser than desired.
Can I please ask, what is the best way/techniques to hone the mold out? Is this even effective?

Thanks in advance

[mattw]

Lawrence, this is what you need to do. I just opened up a mould that was old and dropped quite a bit small. It is much easier once you have done the first cavity, it all starts to make sense.

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

[JonB_in_Glencoe]

I moved your thread to a more specific section, you should get a lot of responses here.

[LawrenceA]

That is awesome Mattw!
Thanks

[gwpercle]

You're passing up the perfect excuse to buy a new Mould !

But honey...this mould is too small for my rifle , I don't want to ruin it so I have to buy a nice new custom mould that fits my rifle !

Or words to that effect...always be on the lookout for an excuse to buy another mould...
With my limited mechanical ability if I tried to enlarge the cavities of a mould, like in the link in post # 2 , No two cavities would be the same, maybe even lopsided and then it would be useful only as a fishing weight on a trotline ...
It would be best for me to buy another mould .
You can never have too many boolit moulds !
Gary
mechanically uninclined

[longbow]

Also look here:

http://castpics.net/dpl/index.php/the-library/moulds/281-lapping-301
http://castpics.net/dpl/index.php/the-library/moulds/23-modifying-molds/308-beagling
http://castpics.net/dpl/index.php/the-library/moulds/23-modifying-molds/254-mold-lapping

Lapping isn't really hard and taking out up to about 0.003" is reasonably easy... 0.001" is easy, 0.002" a little harder and 0.003" starts to become work. Really the "work" is in checking and making sure you keep grit from between mould halves so the cavities don't start to oval which is easy to do it you are not careful.

Since the mould is either mehanite or steel depending on age it will take a bit of time to lap out by hand but going slow is not a bad thing.

The second link on Beagling might suffice for your needs. While Beagling makes oval boolits they are symmetrical so not out of balance. You can get up to about a 0.003" larger boolit from an existing mould this way. Sizing tends to make them cylindrical again but larger diameter... assuming you have the right sizer diameter. Beagling is easy to reverse as well since there is no permanent change to the mould.

However, if the mould is of no use to you as is then you may as well try lapping it, or sell it and buy an NOE or Accurate mould that does cast the right diameter for you. NOE has a variety of cavity sizes to suit most commonly available guns in the bore sizes they tend to want and using ACWW. Accurate will make what you want and it will cast at exactly what you want.

Longbow

[country gent]

Lapping is a straight forward process. Its as old as the pyramids. Granite surface plates are still resurfaced with this process. Its a very accurate precise process. Several issues can be addressed with it in moulds. size, finish, concentricity.
The process isn't hard but needs to be done right with attention to detail. One problem is deciding where to start grit wise in relation to how much you want to remove from the mould. Lapping in a mould is 2 for 1 every .001 removed is .002 on dia so in reality you want to remove .0015 on a side.
Work slow by hand in a supported position. check often by casting bullets and measuring them.

Materials needed are 2 steel plates, a tee type tap handle, length of 1/8" key stock, lapping compounds in various grits. solvent, rags and brushes.

Cast several good bullets from the mould and drill a hole in the base for the key stock to git in. epoxy this in place. Make 2 to 3 lapps up.
Lightly coat the one plate with compound 320 grit or so to start with. set a lap and bullet between the plates and roll under medium force to impregnate it with compound
Mount in tap handle and gently insert into mould cavity. holding in a vise
With a tapping motion work back and forth 2-3 times 1/4 tur or so rotate repeat and work thru the 360* rotation 3-4 times.
Remove lapp and clean. Heat mould and cast several good bullets and measure.
If your close wipe down the plates and with a new lapp impregnate with 400 grit impregnate and repeat thru to casting and measuring. I sometimes for to 600 grit but my final is flitz or shimichrome for final polish.

while valve grinding compound is mentioned a lot its not truly a graded grit size and may be coarse for this. I much prefer true lapping compounds. Here a teaspoon of each goes a long ways. Also as you work the lapps the compound breaks down becoming finer as you go. There are ways to "Grade" your own grits also. Light oil or water depending on compound helps keep the grits cutting cleanly.

[R. Dupraz]

I'm with mattw's suggestion on this one without a doubt. Being a cast bullet bench rest shooter, I am have an obsession with details and Saxguy's (weet) method for lapping molds produces. A few days ago, I used his procedure again to lap another double cavity steel mold out with special attention given to making the cavities as uniform in diameter as I could. An RCBS 30-180-SP. Excellent results with over 90% of the castings from both cavities coming out within .6 of a grain of each other.

The process is not nearly as complicated or time consuming as it might seem. Just follow the directions exactly with attention to the details.

R.

[Mal Paso]

I like using plates to embed the lapping compound into the drive bands which concentrates the lapping on the bands as country gent mentioned.

Arrowhead lapidary has various grits of diamond powder which make lapping iron a little faster.

[LawrenceA]

Thanks Mal
Got some coming
:-)