From my metal working experience, any time I cut, file, turn, or bore metal I get some sort of a burr. Assuming that God has not singled me out for this experience, I operate on the premise that metal burrs occur for anybody who cuts metal. Next time you get a new mold, get out a magnifying lens and look at the edges; I'll bet you a donut that youíll find burrs.
When I get a new bullet mold I run my fingers and finger nail all over the inside and outside of the mold to find the burrs. Some times I can feel them and other times I need to use an Exacto knife blade and the magnifying lens to find and cut off the small burrs.
Iíve used nail sets, because they are hardened steel, or masonry nails for the same reason to gently run around the edge of the mold cavity to burnish off small burrs from the cutting of the cavity. I once found myself in the dog house because I used the ex wifeís diamond impregnated finger nail file for burr removal. She wasnít using it at the time!
Iíve placed the mold blocks on a fine Washita stone and polished the inside surface to clean off burrs from the cutting of the vent lines. A piece of plate glass with some oil and fine abrasive will answer for the same purpose. Sometimes on the outer edges of the mold where the two halves come together there is a burr that will keep the two blocks from joining tightly. Check the alignment pins to see if there is a burr there that will hinder complete joining of the mold halves. The Exacto knife can be used to remove the burr around the alignment pins.
Iíve trued up the sprue plate by polishing it on the same stone or plate glass. The manufacturing process will most likely leave a spot that is pushed out from the sprue hole being drilled. My polishing just cleans up this problem as well as the burrs and sharpens the cutting edge of the sprue plate .
Iíll use dental picks to run down through each vent line to clean out any burrs there. Your dentist will have these dental picks from time to time because the picks wear out, get dropped, and he/she will be throwing them out. Also, the vent line may be blocked where it intersects the mold cavity, because the vent lines are cut before the cavity itself.
The manufactures cannot clean the mold up and remove all the burrs, etc. and still be able to sell that mold for a reasonable price. I accept this, and when I get a mold I take it apart and check it out.