Can I add venting to a mold?

[historicfirearms]

I recently bought a Lachmiller 41 mold and it has no vent lines. It was tricky to cast with but I eventually made good boolits by holding the mold tight against the spout on my bottom pour pot. It was a little slower and messier casting that way which got me wondering if I could add some vent lines? Here is a picture of the mold. Attachment 262146

[popper]

Try smoking the mould including block faces (bic or matches only - no wax). Holds the faces open a smidge so it vents.

[historicfirearms]

Thanks popper, I will give that a try.

[country gent]

You can add vent lines if desired by hand. A vise to hold the blocks, a square smaller is better keeps lines neat and straight, A sharp scribe HSS will work carbide is better, a very fine stone.

Set a block in the padded vise snugly above vise jaws. Lay square so it is where you want the vent line. Starting at the cavity draw scribe 2-4 times to edge of block in both directions, repeat for the desired number of vent lines. Medium pressure and several passes will cut about a .002 -.004 vent line in each side. By starting at the cavity and working out the biggest burr is on the edge of the block not in the cavity. After cutting the lies a light stoning to remove burrs and raised edges.

Another way is to lay a piece of coarse sand paper on a true flat surface and in a straight line and light pressure make 2-3 straight strokes to break up the face surface on both blocks. These fine scratches will vent also.

[Conditor22]

the easiest method is to run a stone or a fine diamond file a couple of times across the inner top edge of the mold from the cavities to the outside. ONLY PUT A VERY SLIGHT BEVEL [look at the vent lines on other molds to get an idea of how little is needed] --- DON'T OVERDO IT!!! it doesn't take much and you can't un- sand/file easily.

Worst-case scenario you could remove a couple of thousandths off the top of the mold IF you go too far. This is not easy without proper equipment

[dale2242]

Some molds just need to be pressure cast.
If you are getting satisfactory bullets pressure casting with it, I would not risk messing it up by trying to vent it.
That`s just me. It`s your mold...dale

[TomAM]

The old Ideal and Lachmiller molds had no vent lines until casters became convinced that they were needed.
A very slight bevel at the top of each half as described by Conditor22, combined with the inevitable gap under the sprue plate, is all the venting needed.

[cupajoe]

Yup, no whiskers from the vent lines or buildup in the ventlines if their are none.

[Drm50]

I’ve never done a bullet mold but have done several custom fishing lure molds than refused to fill out fine detail when it’s on both sides of main body. I can’t think of a bullet shape that would need that.