mold lapping a steel mold

[hornsurgeon]

i got one of the 45/70 lyman group buys a couple of months ago. bullets won't drop from on half at all. i need to beat (not tap) the handle hinge to get them to drop. once out, you can see that it is being held in place in from the bottom lube groove to the base of the bullet. there are multiple seam lines as it is tapped from the mold half. i cant be sure yet, but the cavity may have been cut just slightly off center, and the mold is squeezing the boolit into the mold half. do i dare to lap this mold to tru to remedy the problem?

[JSnover]

Try deburring it first.

[KYCaster]

If the mold is cut off center (deeper in one block than the other) it should be sent back to the manufacturer for refund or replacement.

It will take a lot of lapping to help in that situation and the results will probably be unsatisfactory. Lapping will open the cavity parallel to the parting line faster than in the other axis. This results in an out of round condition which may help your situation, but would cause a different issue that you may or may not want to deal with.

Jerry

[WHITETAIL]

You have a couple of options.
1- try taking a tooth brush with tooth paste
to the mould.

2- you could try using a regular pencil to
the mould.

3- send it back.

4-I would try moulding a boolet and
lapping it a little.:holysheep

[longbow]

If it appears be cut significantly off center I would send it back but it may be just small burrs or minor imperfections.

If so, I would use fine valve lapping compound to smooth it up. If it looks like just small burrs maybe a polishing compound like JB bore paste or similar would be enough.

What I usually do when lapping to smooth or open a mould up a bit is:

- cast a couple of bullets per cavity
- drill them in my lathe (can be done with drill press or even by hand)
- cut the heads of some wood screws
- run them into the bullets
- file a small flat down the side of the bullet
- put valve lapping compound on the flat (it gets everwhere anyway)
- close the mould on the bullet gently in a vice (only one cavity at a time)
- use an electric drill to slowly turn the bullet
- when it gets slightly loose take the mould out and clean it up to make sure there is no lapping compound on the faces
- re-clamp the mould in the vice and turn until the lap is slightly loose
- repeat for the second and other cavities with new bullets
- clean up the mould to get all the grit off and cast to see how it works or if the size you want is being cast
- if so you are done other than I usually use the same lap to lightly finish each cavity to make sure they are as close as possible
- if not then repeat

If you are just de-burring it doesn't take much and you might want to start with just a bullet and no lapping compound to shave the bullet down a bit then add the lapping or polishing compound.

Also, some people like to cast with the sprue plate open and a nut over the cavity then use a wrench to hand turn the lap. This might be safer for de-burring ~ slower but safer. For iron moulds, I usually use a drill but I am also usually opening them up a thou or two.

Aluminum or brass moulds are much softer so lapping compound may be too agressive. JB bore paste or other polishing compound or even toothpaste would be a better choice there.

I just lapped a bronze mould with valve lapping compound and it cut very quickly. I almost over did it.

Longbow

[hornsurgeon]

i was hesitant, but lapped using 600 clover lapping compound. i ended up having to lap quite a bit to get it to drop, (at least 5 minutes total spinning it in a low speed drill press) but it now drops a nice .460 round boolit. now if i can only get the hang of lapping a lee mold.