Bell Curve?

[swheeler]

I typed out a nice long winded post on what I did and "blink" Cast Boolits refreshed itself-everything gone??????????????????????????????????? Soo here's the short version. I cast 138 boolits out of 9/1 alloy, 457/450/F Lee mold. They drop around 456 grs, .460+ dia.. The very first boolit cast was rejected because of severe frosting, all other boolits were kept, no alloy was added to the pot after starting to cast- dross was skimmed several times, temp was adjusted down as alloy was used, BB was employed and they were ladle cast. All boolits were weighed on RCBS scale, no guesstimating, the pointer had to hit zero line. They didn't form a bell curve, more like the rocky mountains! 27 boolits had a slight tear on the bases, all looked lightly frosted all over and completely filled out.
138 Total
heavy 457.1
light 455.2
ext spread 1.9 grs(about .4% variation)
457.1-3
457.0-4
456.9-36
.8-11
.7-16
.6-1
.5-18
.4-2
.3-0
.2-2
.1-5
456.0-22
455.9-4
.8-3
.7-5
.6-0
.5-2
.4-1
.3-0
455.2-3
I plan on shooting the 10 lightest and heaviest into one 50 yd group to see what happens. Picture of the curve-SPIKES

[Dale53]

First of all, big bullets are definitely hard to cast. The nearly two grain variation is not as bad as it sounds. When I was shooting BPCR (30/1 lead/tin alloy) my criteria was + or - .6. I considered that match grade. You're not very far from that. My rifles were and are competitive.

Dale53

[Buckshot]

...........A 2 grain variation should do for all general shooting. If you skimmed off dross instead of fluxing you'd loose a bit of tin, but apparently not enough to affect much as the boolits would have been tending heavier.

I'll bet you were using a bottom pour pot. As the level dropped you'd be getting slightly lighter slugs. Block closing pressure will also affect weight.

Very interesting results. All that scaling is finicky fussy work so thanks for doing the work and recording the results for us.

...............Buckshot

[Bass Ackward]

Scott,

If you have enough bullets, take ten of the extremes and shoot them too. Then you can know a worst case also.

Then don't forget to post results. Thanks

[Wayne Smith]

And you don't have near big enough of a sample size to expect a bell curve, either. You'd need thousands to tens of thousands of bullets to get that.

[Dale53]

Sometime ago (less than a year or so) I was introduced to the Cabine Tree "Mould handle lock" and bought one. It DID reduce my bullet weight differences markedly. I am now shooting schuetzen and the requirements are SO high that I need every advantage that I can get just to "stay in the race".

If I were still shooting BPCR silhouette, I would be using the Cabine handle as well. For those who have not seen one, the mould handles lock similar to a vise grip. Each and every bullet is cast with the same pressure on the blocks insuring that the "hole" that you are pouring bullet metal is the same size each time. Here is the web site:
http://www.castingstuff.com/cabinetree_loading_products.htm

Just scroll down to the "Locking mould holder".

Understand, I only use that mould holder for precision bullets for my competition rifles. I just do it normally (as the actress said to the Bishop) for hunting rifles and all my pistols.

FWIW
Dale53

[JohnH]

And you don't have near big enough of a sample size to expect a bell curve, either. You'd need thousands to tens of thousands of bullets to get that.

Waynes right, and your bell curve won't look like a bell curve either. You will have several peaks either side of a norm, could be one more on one side than the other, and it will change with the pot level and the temp level of your melt as you add alloy back.

Since this is a manual operation, a lot of statistical control science doesn't really apply, as each cast is in a way a process of it's own. SPC is meant to monitor the repeatability of a purely mechanical process. It would be better applied to a Magma Master Caster. Simple weight segregation is good enough for most any of our purposes.

[swheeler]

Got to the range to shoot some of these boolits. All were loaded in Hornady 458 Lott brass, fireformed in the rifle and loaded with 460 Weatherby RCBS dies, FC210M primers and 30.0 grs 2400 powder, Lyman super moly lube. Temp was 40 deg, wind blown sleet.
The first 5 shot group was with the 5 heaviest boolits out of this run(cold clean bbl)
457.1
457.1
457.1
457.0
457.0
50 yd=1.806 in
the second group was with the lightest boolits(cold cleaned bbl)
455.5
455.4
455.2
455.2
455.2
50 yd=2.451 in
No conclusions were drawn on such a small test, and weather conditions could have played into the outcome. Looks like I got rid of my" first" shot flyer by switching lubes.