Opening Up a Mold

[rescuerandy2]

Good Evening. I have a .314" mold that is not working well for my Lee-Metford Mark II*. Would like to find someone who can open the mold to .318". Thanks, Randy

[mattw]

You could lap it in.

[high standard 40]

Erik at Hollow Point Molds used to perform that service. He did two molds for me. Not sure if he still does. Wouldn't hurt to ask.

www.hollowpointmold.com

[rescuerandy2]

NoGo on Erik.

[StuBach]

Lapping might be your best bet or sell it and use funds to sponsor a new mold with right dimensions. Possibly one from Accurate depending on your specific needs since his are custom to order.

[country gent]

What are the blocks material ? Aluminum is a little harder / fussier to lap, But can be "lee mented on the faces with thin tape. Search the site for leementing. Brass and steel are easier to lapp and respond better.

Heres how I lapp a mould in to increase the size. Its a slow process but very accurate and you get very good bullets.

Cast 4-5 good bullets if a multi cavity id bullets to cavity 1- ?
I do this by hand so a stem needs to be added to the bullet.
use the blocks and sprue plate to spot center of the bullet with a small punch.
move sprue plate and drill a blind hole a 1/8" X 1 1/2 piece of key stock fits in. Be careful to hold center and not break thru.
glue the key stock in the holes with epoxy and let cure
with 2 pieces of flat stock spread a light coat of lapping compound on 1 I normally start in the 400 grit range unless Im correcting a bad finish is all. Now roll the bullet thru this spot between the 2 plates to impregnate the bullet. Use light force to push the compound into the bullet.
Mount the bullets stem in a tap handle and carefully insert in mould.
close blocks gently with firm pressure. A vise is helpful but a rubber band will do.
Now is the important part of this. Dont spin the lapp use a tapping type motion. 1/4 to 3/8 rotation back and forth 2-3 times rotate 1/4 turn and repeat thru 2 - 3 rotations in each cavities. . Then clean and cast some good bullets to check progress

Tools Materials needed
t type tap handle
vise drill press is best but with care a drill motor
Drill bit the same dia as corner to corner on a 1/8" square
center or prick punch

Lapping compound 400 grit - 600 grit Diamond compound works but is much slower, better finish It can be found for around 15.00 a small tube.
epoxy JB weld is real good
clean rags towels and solvent.

Work slow and careful. Make casts often to check progress.
When done correctly bullets will be truly round and a very good surface finish.

[mattw]

I see country gent beat me to the post, we are doing things a bit differently... Pick your workflow and have at it. The results are really worth the effort.

I am sorry for my tiny reply earlier. I was on my phone and I hate serious typing on the damn thing.

I have had a number of Lyman moulds over the years that were .001 to .003 to small or out of round as evidenced by uneaven sizing of non-opposed sides. Here is how I correct that problem, take it for what it is worth but it works.

You can increase the size of one or all driving bands, make lube groves shallower, make a bore ride nose a tiny bit bigger or all of the above at the same time.

1) cast a small number of bullets from your mould, keep cavity 1 and 2 in separate piles.
2) decide what area you need to increase in diameter and decide how far you need to go.
3) center punch and drill the bases of 2 bullets from each cavity, I drill small holes. These should be as centered as possible.
4) locate an easy out that fits the hole in the base and a hand tap wrench to turn it with.
5) locate 2 medium cut metal files
6) locate lapping compound, I use clover 1A (320 grit) to start and 3A (500 grit) to finish. The 3A has been discontinued for many years, go 2A or 4A. Mine is so old that it is in metal cans with pop off lids. This has the grit media suspended in a heavy grease
7) If you are working on driving bands, place a small dab on one file flat on a table. Set the bullet in the dab and then place the other file on top of the bullet and roll the bullet by pushing down and moving the file forward and backwards. This creates a crosshatch on the bands with the compound inbedded into the surface.
8) Remove excess compound from any areas that you do not want to lap
9) Put the bullet into the cavity that created it and close the mould on it.
10) Insert the easyout into the base of the bullet and hold the mould tightly closed with your handles and turn the lap in the cavity. It will be very difficult at first but will get easier, you may even need to release some pressure on the handles. After a good number of turns removed the lap and proceed to the second cavity with the bullet made from that cavity.
11) Clean your mould very well!
12) Inspect each cavity and repeat with a second bullet. If little work is needed you could switch to fine grit now to really make the cavity smooth. But, I find that 1A is almost as good as the original cuts and 3A is just beautiful.
13) Clean and inspect again.
14) Warm the mould and cast new laps for another go, if you need even more expansion.

Do not put the bullets in your pot, they contain grit that you cannot remove!

The above process can be applied to just the nose as well, for example a bore ride bullet that needs to be just a little larger diameter for accuracy.
This is a slow process, but is often rewarded with a more concentric bullet, a mould that drops bullets easier and a bullet with a correct fit for your gun. Parts of the cavity will be shiny, bare steel. Casting with it for a bit will bring the color and limited protection back to the mould. I have only applied power tools to the process one time, I had one mould that dropped over .003 smaller than it was designed to drop and even with 1A going was very slow. Change laps often, cast new ones often and measure progress.

Remember, go slow, never more than 2 laps without casting and measuring and never, never put that bullet back in the pot!