Lee mould in 45-70 The 405 Lee measured .457. My bbl slugged at .4585. So I needed to be about .003 larger.
Check your bullets for roundness before you start lapping. This will be a good guideline for checking roundness later when you start lapping. You may even improve on the bullets roundness by lapping.
Make a few good hardcast bullets. While your mold is cooling, drill a small hole in the base of one of the bullets as close to exact center as possible. Use a lathe if available. (Best)
If it is off center you can ruin up your mold.
Chuck a 2 - 2 1/4 inch drywall screw into a variable speed drill. Thread the bullet onto the drywall screw.
Use polishing compound because it removes material much slower than valve grinding compound and is more forgiving and easier to clean up.
Put a light coating of polishing compound evenly all over the bullet and close your mold around the bullet. Run the drill very slowly to get the bullet to seat properly into the grooves of the mold.
Once set slowly start the drill, using very light pressure on the mold handles. After a minute or so the bullet will be seated perfectly and you can add more compound.
After a couple of minutes of lapping, you will need to clean the mold really good and cast a couple of bullets and check the diameter. You may have to do this three or four times, but it is better than ruining the mold.
You should not try to remove more than .002 - .003 in this manner using a hand drill. If more material is removed errors can start creeping into the mold, so if necessary proceed at your own risk.
If there is any indication that out of roundness is happening you should stop right there. This occurs at the base of the bullet first. You should also add polishing compound for every minute of lapping.
It's tedius to do but if you do it right the bullets come out better than before lapping. Just take your time and check your work very often and it will turn out fine.
I learned this the hard way and had to replace a couple of molds before I got smart about checking my work often.
Use this method to polish new molds without removing any significant amount of material. Bullets from a mold treated like this are less prone to sticking in the mold. They have a very smooth overall appearance with no machining marks evident.
You can also lap a sizer die using this same method. Lee sizers also only go up to .457. Mine sizes .459 with #2 alloy now and is perfectly round. It takes a bit longer but it works. PC
Check your bullets for roundness before you start lapping. This will be a good guideline for checking roundness later when you start lapping. You may even improve on the bullets roundness by lapping.
Make a few good hardcast bullets. While your mold is cooling, drill a small hole in the base of one of the bullets as close to exact center as possible. Use a lathe if available. (Best)
If it is off center you can ruin up your mold.
Chuck a 2 - 2 1/4 inch drywall screw into a variable speed drill. Thread the bullet onto the drywall screw.
Use polishing compound because it removes material much slower than valve grinding compound and is more forgiving and easier to clean up.
Put a light coating of polishing compound evenly all over the bullet and close your mold around the bullet. Run the drill very slowly to get the bullet to seat properly into the grooves of the mold.
Once set slowly start the drill, using very light pressure on the mold handles. After a minute or so the bullet will be seated perfectly and you can add more compound.
After a couple of minutes of lapping, you will need to clean the mold really good and cast a couple of bullets and check the diameter. You may have to do this three or four times, but it is better than ruining the mold.
You should not try to remove more than .002 - .003 in this manner using a hand drill. If more material is removed errors can start creeping into the mold, so if necessary proceed at your own risk.
If there is any indication that out of roundness is happening you should stop right there. This occurs at the base of the bullet first. You should also add polishing compound for every minute of lapping.
It's tedius to do but if you do it right the bullets come out better than before lapping. Just take your time and check your work very often and it will turn out fine.
I learned this the hard way and had to replace a couple of molds before I got smart about checking my work often.
Use this method to polish new molds without removing any significant amount of material. Bullets from a mold treated like this are less prone to sticking in the mold. They have a very smooth overall appearance with no machining marks evident.
You can also lap a sizer die using this same method. Lee sizers also only go up to .457. Mine sizes .459 with #2 alloy now and is perfectly round. It takes a bit longer but it works. PC