Mold dropping different weights

[Wm Cook]

My 2 cavity Lyman 225438 mold (2010) Has one cavity larger than the other. The far cavity is averaging .4 of a grain heavier than the near cavity. My solution has been to separate them as they drop, weigh, sort and keep separate for accuracy purposes. Is there any solution out there that could lap the smaller near cavity to equal the weight of the far cavity.

Why? In the winter I play in my shop with a 10 yard range and I have a hooting good time juggling powders, powder charge, primers and seating depth looking for subsonic 5 shot groups that are under .0999. With the loading bench 15 feet away and in a controlled 70 degrees environment I can spend hours playing with combinations. And once you get a consistent load worked up it’s a lot of fun looking at two, three or four one hole groups on the same target. I’ve actually shot 5 shot groups under .00XX that could be repeated in the range of .0XXX and under.

I understand that shooting screamer groups in those conditions is certainly not applicable to the real world but i’m just competing with myself and having fun. And by the way, if the best combination of depth, primer choice, powder and powde charge is shooting .2000 at 10 yards it just ain’t gonna get any smaller than 2.000 at a hundred yards.

So I sort and shoot Bullets +/- .000. Which i know is further diluted by my RCBS scale that can only measure to +/- .001.

I’m a geek but I can live with that. Thanks for listening.

[country gent]

Lapping to change weight can be done. I've done it to change size of a bullet a few thousandths, to smooth out a mould, or to help with release of bullets. Its a slow proves for size since the base band can be measured until you get very close. Lapping for weight would mean lapping a little, heating and cast perfect bullets waiting for them to cool and weighing then lapping more after the mould cooled down.

Here I think I would mark the nose in one cavity with a prick punch or o letter punch so the cavities could be easily segregated and shot as batch lots each. In this way you get 2 lots of bullets each session ( same number of bullets but in 2 batches). Lubing and sizing in the 2 groups wouldn't be a big issue and neither would loading. Sorting would be the extra step in this.

Out of curiosity how much do the cavities vary in size? dia both bands grooves and gas check, length base nose and overall. This will give an idea of how much needs to be removed, and possibly where.

[gunarea]

Hey Wm Cook
In your case there is both a possible answer and solution. First is to examine your casting procedure. A hot cavity will throw a heavier slug than a cooler cavity. In identical size cavities, continual front to back, or also continual back to front filling, will produce different cast weights. Even a two cavity mould will have one end hotter with continual front to back filling, or also continual back to front filling. If your casting procedure does not include reversed filling direction on each cycle, then do so and note the difference. This same practice can be used to correct slight differences in mould cavities. In my particular mould, a 4 cavity, it is possible to fluctuate weights up to 2gr with temperature. Your affliction to detail is nothing new, many of us still bear the yoke of OCD. Go find some benchrest guys and you will feel at home. Here is some food for your geek appetite.

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Temperature monitoring is but one step. Alloy consistencies is another. The most difficult to control variable is in your mirror.
My pitiful approach begins with consistent liquid temp, a PID is mandatory. Consistent empty receiving mould temp will help a finished weight consistency. Cadence will greatly affect finished weight consistency. Cooling the mould and alloy in a consistent manner is a subject of great ignorance for the majority of casters. Opening mould temp, rate of cooling, receiving mould temp, relative reservoir head, HOW BAD IS YOUR OCD?? My study produced many more questions than answers.
So before making mods to your equipment, make sure the human variable won't introduce further error into the process.

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Those are Florida state titles just since 2000, although I do not enjoy casting "match" projectiles, I do like gold medals. My shooting coach, mentor and friend, George Forest once said "you ain't that good, everything else better be perfect". He is right.
Roy

[gunarea]

Hey Wm Cook
Have you gotten your weights closer? Did you measure the slugs? Always interested in positive progress.
Roy