Why You Should Weigh Your Bullets

[Lead pot]

Larry,

You make some good posts with your cast bullet information.
I'm very annal with my cast bullets because I shoot most matches at long range and for this purpose you need to spend time getting the proper alloy and put that alloy in a mould casting a good bullet.
I have spent a lot of research time with alloys that will hold the bullet from getting setback that will result in bad accuracy if the operation gets moved out of balance.
Most of my shooting is with bullets 500 grains plus and the the way I cast I seldom get a bullet under one grain light from the heaviest when ever I weigh them, seldom do I do that
What I found causes some of the light/heavy variances is dross getting into the cavity from the ladle spigot. I have split light bullets to see the voids and all I have ever found is dross.
Also I found that improper mixing the alloy. Tin is light or if one uses ww a the lead mix the WW are lighter than the lead and if you don't get the mix blended you could pick up the lighter or heavier mix and the results will be weight variance. I mixed alloy in the 20# Wagge lead pot with just dropping the lead tin ingots and storing it with a spoon a few times with flux and I found perfectly cast bullets weighing as much different as 1. 7 grains.
The next batch was mixed with the same amount of lead/tin by weight but I used a paint mixer you put on a drill motor and I mixed and fluxed that pot using it for a longer time frame and cast a bunch of bullets and only 3 out of 50 went a 1/2 grain light from the heaviest. I don't know if a proper mix does this or not but I spend the extra time doing it.
A sprue plate to loose will cause heavy or light even when properly filled mould.
When you get bullets like this after they leave the muzzle looking like this.


The results should look like this if you do your part behind the buttplate and find the proper powder load.
The first two targets were ladder loads at 100 yards and the small target was a follow up test at 200 yards.
A cast bullet will shoot well if all components come together properly.
Just don't push them to hard

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[Castaway]

I have a nose-pour Hoch mould that does well, but the group above was with a Lee 500 grain Govt style bullet.

[HWooldridge]

The reason nobody charts a true bell curve is because you are dealing with a mold that has a finite fill point. I worked in the plastic injection molding business for almost 20 years and we saw this everyday. When the mold is closed and filled, the only thing that can cause heavier than max boolits is a blown mold, i.e., separation at the parting line. Other possibilities are slight inconsistencies in the alloy, adding ingots to a melt might change the weight over a session. Larry's chart is pretty much what I would expect to see - a nice tight distribution when the mold is filled to capacity.

[Shanghai Jack]

Just to add to the discussion - for my schuetzen competition with plain base bullets

I cast in a single cavity mold nose pour mold with an indexing mark working on the assumption that no two cavities will be identical.

I melt, clean and flux in one pot and transfer to another that never sees anything but the cleanest alloy I can make. Cleanliness is next to godliness.

I use the largest amount of 24-1 alloy that the second pot can hold no matter how many bullets I am casting and do not throw sprues back in the pot or add alloy after I start.

I watch the temperature like a hawk. The large amount of melt tends to stabilize the temperatures. 200 168 grainers uses about a quarter of the pot.
Going the Pope and Mann route I keep the bullets in the order cast. For a hundred round match I'll cast about two hundred.

A quick visual inspection eliminates those with obvious external physical defects - e.g. rounded bases, ugly grease groove, dross inclusions, or anything else. I'll also discard any frosted bullets but I don't get a lot of those.

Depending on my mood, this usually eliminates 50 or so. They go into the box for scrap lead along with the sprues. I use this scrap for non critical casting like .45 caliber round noses and such stuff.

Then, with the bullets still in as cast order I weigh. Since my alloy is always the same I don't do the bell-curve thing - just discard obvious outliers which probably represent an internal dross inclusion, void, failure to completely close the mold, etc.
This usually, depending on my mood once again eliminates another 5 - 10.

Then I lube and shoot in order cast indexing the bullet to the bore. If its going to be a congenial shoot, I don't lube until I'm ready to seat the bullet into the gun. Nothing like fresh lube. I reserve the first and last 10 cast for foulers and sighters. If I don't use them when the match is over they go in the scrap.

I know its probably anal but I really enjoy casting what I consider to be the absolute best bullet I can. Its a long process but, for me, its worth it.

Don't even get me started on lubes. I'm still looking for the odd bottle of sperm whale oil.

If you were using plain base bullets I'd say that you had damage to the steering end (base) of the bullet. Perhaps the seating of the gas check is slightly askew or its separating at the muzzle or somewhere down range.

I wouldn't think that losing lube in a part of a grease groove would be significant enough to cause a 4 inch flier.

Most often when I see a uncalled flier that I can't blame on a bad bullet its something I've done to the gun like resting the forearm on a different spot on the rest causing a change in barrel harmonics or shooting too rapidly but its not usually 4 minutes of angle.

[Bad Ass Wallace]

There is not just "one thing" that is the controlling factor in shooting good groups. Boolit weight is one but so to case preparation, neck turning, primer pocket deburring, trimming to length etc. I weigh all boolits into batches. No matter how close you inspect them some wlll weigh heavy and some light. In my 30.06 substituting Federal LP primers for LR primers annulled the occasional flyer.

My load of 31.5gns of 3031 showed just 16fps spread over the chronograph. Prior LR primers gave an xtreame spread of 82fps, giving vertical stringing.