Analysis of cast boolit weight variences

[rbertalotto]

I was reading the Lyman's Cast Bullet Handbook, 4th edition. One of the authors talks about only keeping bullets that fall within .6 grams of each other. Six Tenths of a grain. I was surprised at that number so I went to the "lab" and did some weighing.

I used the same technic as spelled out in the handbook of making a visual chart to log the various weights.

First up are some lubed bullets cast from Wheel Weights.......



The next group was from "manufactured" bullets that I had bought before I started casting myself.....



And another series of "manufactured" bullets....



This group is from bullets I cast yesterday. Not lubed yet.....



And finally a very surprising outcome. What's up with those Bad Boy bullets????



Comments? Anyone else ever weigh their boolits and see how consistant they are?

I'm going to keep accurate records as I shoot these boolits to see how this affects accuracy.........

[303Guy]

Interesting results - and layout.

Funny how there seems to be weight groupings like that. I've found that there will be gaps in the weight range too. Mold or alloy temp doing it? I bought myself a scale that has a 0.01g resolution for NZ$18 (less than US$). It's faster and more accurate than my NZ$100 one!

[John Boy]

Anyone else ever weigh their boolits and see how consistant they are?

Only for bullets that I shoot for BPCR and Schuetzen - long range, 200m to 1000yds in the 165 to 570gr range. My 45 Colt ones - don't really care but usually they are with 2 gr variances
I see that each of your bullet batches have a bell curve. This is normal but the variances can be tightened with several casting techniques:
* Only drop poured bullets when the pot/mold temperature produces a sprue puddle that frosts at 5 - 8 seconds.
* Then hold that temperature consistent for the whole casting session
* Pour your lead: tilt mold to the right or left - put the ladle spout firmly into the sprue hole - turn the mold vertical - keep a good head pressure for a 5 second pour with the spout still firmly in the sprue hole. Your bell curve will tighten up if you maintain the same smooth consistent rhythm

I cast for 0.5gr bullet variance and weigh each one. Those outside the curve I use for practice.

[DrB]

Neat plots!

How many cavities is each mold? Can you annotate your original post for each plot of weight's for your molds with the number of cavities?

I'd bet the multimodal plots are from the different cavities... Though it could also be temperature related I suppose. So I'm wondering if there are multiple cavities for each plot with multiple modes. If you have two modes from two cavities that can give you three peaks in the distribution from the overlap of the tails.

That could be making too much of this though as your sample size is relatively small from the standpoint of resolving a distribution. To get the tails pretty well and get a fairly smooth distribution curve you might do several thousand samples (!). 10,000 is the number we'd usually use in numerical studies, but that's clearly off the deep end for what you are doing.

You might cast three or four more noting the cavity and plot them to see if they consistently fall into one of the humps of your plots.

[rbertalotto]

First mold is Two Cavity. Not sure what the "manufacturers" are using. The two Lyman molds are single cavity.

My furnace (melting pot) uses a PID to control temperature within 15 degrees. I'm running my allot at 725 degrees.

My molds have a hole drilled and a temperature probe attached. Mold are held to 350 degrees +/- 10 degrees.

My three rifles that use these bullets (1895 Marlin, Winchjester 1885 and Pedersoli 1874 Sharps) all 45-70, all shoot under 3" at 200 yards. The Marlin has irom sights, the other two have Leatherwood Malcolm type scopes of 6X.

I just find it interesting that there could be this type of varience, especially those Postells with a bunch of "Bad Boys".....We're talking nearly 10 grains over the average. I didn't even think this was possible.

The reality of all this is, if you don't weigh and sort your bullets, you are going to have all kinds of fliers I suspect.

[waksupi]

If you get some of Gussy's handles, you can cut this variation considerably.

[Doc Highwall]

I will second the handles from Gussy.

[leadman]

The bad boys might be larger in diameter. Sometimes a speck of lead will keep the mold open just a touch.

[1Shirt]

Much of weight variance is due to casting technique, speed of casting, consistancy on the part of the castor, etc. Any variance of timing, can be a difference in weight. For handgun, I am satisfied with 1/2 to 1 grain difference, as I am not a match shooter. For rifle in large cals above 30, am satisfied with 1/2 grain variance. For small cals 22-6mm, I want exact weights and seperate them accordingly on the basis of bell shaped curve. The ones on either end of the curve go back in the pot- or in the cull box to be used only for plinking. Good thread!
1Shirt!

[John Boy]

For folks that weigh by 0.5gr increments, here's an easy way to make a 'Bullet Board' for the measurements:
* Put a long piece of masking tape on your work bench
* Mark it in 1/2 gr increments:
0 - .5 - 1 - .5 - 2 - .5 .... out to 9.5
Lay the bullets under the specific increment. Then you can double or triple stack them depending on how many you cast by standing a couple bullets at both ends of the stack to keep them from rolling around

[rbertalotto]

OK, I give up!

Gussy's handles????????????

[DrB]

Fellow named jim gussy of cabintree sells locking mold handles that are supposed to tighten up roundness/weight of boolits by ensuring more consistent pressure on mold halves.

I've never used them or heard of 'em... I had to look 'em up in case one of these old guys was sending us after some "shore line."

I take it they help...

Thanks again for posting your plots... Interesting results, especially given how much you are doing to control lead and mold temps. If you happen to experiment with your technique and repeat your plots, please share them. Would be great to know what ends up working or not for you.

[Doc Highwall]

The handles have a over cam feature that give the exact same closing pressure each time the mould is closed. If you have a high gripping pressure when you start casting and as your hand gets tired the lighter gripping pressure will make bullets that are heavier. For the best match bullets these mould handles have no peer.

[reloader28]

I've never weighed pistol boolits.
I weigh all my rifle boolits and keep them within a .5 grain.
My .223 cal boolits are usually kept within .2-.3 grain.

I used to get 2 grains difference in my 150gr RCBS 30 cal 2 cav mold until I figured out the cavities were a tad different. I beagled one side out and that cut it back to only 1 grain difference.

I made some Lyman 173gr FN 30 cal single cav one night with 50/50/2% alloy and in 200 boolits, I threw back only about 9 or 10. The rest were all within .3 grain.

The planets were all aligned perfect that night.

[geargnasher]

I've done that too, but it's been a while. Doing it several times isn't the most fun I can ever remember having, so thanks for posting your work.

Gear

[noylj]

Each cavity will cast a little different, and I expect commercial casters use two-cavity molds when they can.
I don't know what current knowledge is, but I always felt that if I didn't flux frequently, my alloy would shift.
I have found that, for pistols, the extreme light and extreme heavy bullets tend to shoot just all well as the bullets in the peak(s) in the bell curve(s).
Since these appear to be for a rifle, you might want to segregate by weight and see how each set of bullets groups in terms of group size and location on the target. This will tell if there is any "thing" to correct.
I know that I felt that the light bullets MUST have voids and would be inaccurate, while the very heavy bullets must have the least voids since there are no impurities heavier than lead that should be in my alloy. However, with my pistols, I never saw any difference.

[Bret4207]

Grams or grains? 1 gram is 15.4 grains.

[rbertalotto]

GRAINS!!!!!!!!!!! Sorry, I corrected the OP

[HollowPoint]

I did a similar test back when I first started casting and I got results that resemble yours.

Because I was new to casting I really had no idea why there would be such a variance in weight.

I'm still not totally convinced that any individual reason sighted here is directly to blame with these different weights from the same batch of cast bullets. I suppose it's a combination of various contributing factors.

Now days if I'm looking for Load-Work-Up precision, I sort them by weight.

The only difference for me is that I can live with cast bullets that fall within 2 to 2.5 grains difference. This is for my rifle bullets. Pistol bullets generally don't get this kind of weight sorting.

Why 2 to 2.5 grains you may ask? Well, when I work up loads for my rifles, I use the "OCW" method. My charge weights are done in .3 grain increments with any given cast bullet. These cast rifle bullets fall within 2.5 grains because I've weight sorted them.

I don't know if this makes any sense at all to anyone else but me. I'm not trying to come across like my rationale is right or wrong compared to anyone else. It's just the way I work up my loads. It always seems to work out well for me given enough time and testing.

("OCW" = Optimum Charge Weight.)

HollowPoint

[6.5 mike]

Thanks for the info on Gussy's handles, I've look at them on his site thinking they would help me. I do weigh all my boolits when first using a new mould. What I do if it's a 2 cav, is mark one (usually the front) with a marker so I know which one came from which cav. After they cool I take them in the house to weigh & measure, use an elec scale & mic. SWMBO says I get to play with my toys longer this way, lol. The pistol boolits are just to see if the specs are close to as what it should be, & the rifle are checked closer. I do 10 of each, check 5 that day, & do the other 5 when I get back off the boat. This gives the 2nd batch 2 to 3 weeks to age.
I got a rcbs 7 mm 145 sil from a member here a while back that drops so close together if I hadn't marked them I would not have been able to tell which cav was which. Brp & Noe moulds are the only others that do the same for me.