Warped mould

[MIEagle]

I acquired a used mould that appears to be warped when looking through the cavity towards the nose with the blocks held together. It has the letter "J" stamped on the short side of the block towards the handle, is iron, and appears to be a copy of the 40-400 BPS RCBS bullet. After casting with it, it leaves fins on each side of the bullet which I remove with my fingernail or dull knife blade. Although it shoots well in my .40-60 Maynard 1875 Sharps, it is a real pain to scrape 120 bullets before running through the sizer. Can this mould be resurrected? If so, how? Thank you.

[Conditor22]

Pictures would be helpful.
Check both mold faces for any kind of debris/build up, especially around the alignment pins.
One of your alignment pins could be sticking out too far.

[Winger Ed.]

Something might be keeping it from closing all the way.

To check the pins, lay a single layer of Plumber's Teflon tame over the holes and close it.
Do it with a known good mold also, and compare the effects of compression on the tape.

Something else to be aware of is if your alloy is too hot, even a perfect mold can have those fins.

[country gent]

As stated above check pins and also check for burrs and dings on faces and around pins. Also check for small build ups on the faces.

Warped blocks can be fixed its not easy but can be done.
First you need to determine how much they are warped, a true flat surface and precision feeler gages are needed. You don't just want to know they are warped but how much easch block is warped.
Disassemble blocks remove pins and check on the flat surface holding the face tight and inserting feelers to find the amount of warpage. Its usually not a lot on each side.
on your flat surface a light coat of oil and lay a piece of medium emery paper wet dry 320 to start on the oiled surface ( the oil helps hold the paper down flat)
Lightly work the face of the blocks in a figure 8 pattern watching the pattern that forms and for clean up. As the faces clean up and get close to 100% clean up move to 400 grit them 600 grit. 600 should be more than fine enough. Do both blocks. When done clean and dry both blocks and a light coat of oil on one block rub and look at the oils pattern it should be a good coverage.
Now your blocks are again flat and mated together. reassemble the blocks and set the pins to depth. You bullet and cavities will be oval because of the amount removed from the faces. to cure this you need to cast some good bullets as to fill out and Lap the cavity back to size and round.
Last is depending on how much you removed you ,ay need to deepen the vent lines a little with a scribe point and square.
Like I said its a lot of hand work to salvage a mould that's warped but can be done. If you only need to remove .002-.003 from each of the faces and lap back to round its doable

[Mal Paso]

Or just lap the faces back to the outside edges of the cavities if it's a 2 cavity. Leave the cavities round. That should close the gap more than half.