Casting question -- undersized mold, will this fix it?

[lee n. field]

Casting newbie question here.

I have an old Lee .45 mold, labeled 450-200-1R. Round nose, 200 grain, molds to .450. (It's from my grandfather's estate, I have no idea how old it is, but it's at least 20 years old.) I have a handful of bullets that were cast with this mold, and they measure out right on .450. They are a hair on the small side.

What I want, if possible, is to open this up just a bit. (Yeah, yeah, a brand new two cavity mold from Lee is $20. I'm cheap.)

Lee's support site has a FAQ on lapping molds:

Mold lapping

Remove the core pin assembly and sprue plate, and block off the sprue hole in the top of the mold. Lightly clamp the mold in a vise, base up. Suspend a 1/4" or 5/16" tap into the center of the mold, and fill with molten lead. When the lead solidifies, you should have a polishing mandrel that fits the inner diameter of the mold fairly closely. Don't worry if there are wrinkles, the mandrel doesn't have to be perfect. Coat the mandrel with valve lapping compound or Clover compound, or something similar, and using the embedded tap, give it a couple turns.

Will this do what I want?

 

[ranger335v]

Yeah. But do it carefully and slowly with a VERY FINE GRIT or it will quickly be oversize and perhaps oval too.

This IS NOT a precision fix, only a rough and ready way to salvage an undersize mold. The only time I did it was to salvage a .54 cal. Lee mold that otherwise would have been useless to me. I simply drilled a centered hole in an already cast bullet and screwed a brass wood screw into it, then filed a flat side to the bullet so I could put a drop of compound and oil on it and still close the mold. I cut off the screw head so I could chuck in in a slow speed VSR drill while I lightly hand held the mold so the "lap" could rotate without working aganst the wobble of a less than ideally aligned screw.

The surface of the bullets aren't shiney now but they fit my oversized bore and really shoot much better.

 

[hawkeye1]

Do you have any idea what kind of alloy those bullets are. Just an idea, but you may try pouring some with just wheel weight material. That may make a bullet come out just a bit larger. If you go to a softer alloy, you will drop a larger bullet.

 

[lee n. field]

Do you have any idea what kind of alloy those bullets are. Just an idea, but you may try pouring some with just wheel weight material. That may make a bullet come out just a bit larger. If you go to a softer alloy, you will drop a larger bullet.

No idea at all, nor any good way to test lead hardness. I guess I'll just try it.

 

[ReloaderFred]

Actually, a harder alloy will make a larger bullet. Bullets I cast of wheelweights are quite a bit smaller than bullets cast of linotype from the same mold, even though they weigh less. The higher tin and antimony content means there will be less shrinkage, which is why linotype is the alloy it is. It didn't shrink when cast in the linotype machines.

Hope this helps.

Fred

 

[snuffy]

Another method is to get some of the fire lapping compound from midway, wheeler engineering sells it. You simply make a bullet, drill it for a screw, then roll it in the abrasive. It is spun in the cavity to enlarge it a bit.

Fred's right though, a harder alloy will always cast a little bigger. It may be big (er) enough to work for you without enlarging it.

 

[ReloaderFred]

I've lapped sticky molds with a bullet cast in the cavity and drilled for a screw like Snuffy says. I use Flitz Metal Polish and it really polishes the inside of the cavity and the bullets just drop right out. I doubt if Flitz is abbrasive enough to enlarge a cavity, though, aluminum is softer than iron, so it just may work, as long as you don't let the compound go dry and gall the mold.

Hope this helps.

Fred

 

[snuffy]

cast boolits.com

Here's the technique I alluded to, couldn't remember where I'd seen it.

http://castboolits.gunloads.com/showthread.php?t=3172

Donr this way, you can control where and how much you want to enlarge the cavity.

 

[highlander 5]

I have found that Linotype will make the largest diameter bullets but they will weigh 5% less. A block that casts a 400 gr bullet using no 2 alloy will weigh 380-385 gr if cast with linotype.