Weighing cast bullets

[popper]

Several discussions of this. I ran the numbers. A grain of lead alloy is 0.00035 cubic inches, about 0.07" cube. A layer of 0.0002" DIFFERENCE in dia (0.2 width - drive band)for a 20 cal (55gr) is 10gr, 30 cal (165gr) is 30gr, 45 cal (220gr) is 38gr.
So temp ( any) variation that causes as cast dia to change will cause a great difference in total weight.
Edit: got into this discussion as OP thought he could find voids in his cast bullets. A 0.07" cube is big but other variations could hide it, my point. Accuracy - ballistic calculator. Weight does not effect drop due to gravity! Weight does effect inertia! Rotational inertia controls stability and forward inertia (which drops due to wind resistance) increasing TIME that gravity can work on bullet. To simplify, weight variance from A mould makes no difference in POI, a very small % of weight, no change to wind resistance. A large void? Yrs ago I used pin nails to hang bullets to be PCd. Clip off exposed nail. 30/30 RD GCd Lee mould, full loads. NO difference @ 100. I cull as cast bullets visually, not by weight.

 

[Ian]

I'm coming up with about .6 grain on two ten thousandths driving band diameter difference for the .22.

Weigh AND measure for most consistent bullets. 3% weight variance accounts for something less than 1/2 MOA deviation at 100 yards, more at longer distance depending on velocity and whether there's an imbalancing void causing the weight deviation or just more mass due to mould handles not held tightly enough for that pour.

I get 1.5 MOA and often better ten-shot groups at 100 at full jacketed velocity using bullets which have only been visually (and casually, I might add) culled. Weight sorting is a waste of time 99% of the time IMHO.

 

[popper]

I try to make my statements simplified so OP get the idea. I even rounded down the 0.41#/cu" to 40 to account for SB/Sn alloy. IMHO you can see a 5% variation in weight that may make a difference but the variation is more 'distortion' than just weight. I still can't visualize a 0.00034 cubic inch. A 70 thou "cube 'void' is a problem with your casting technique or alloy cleanliness.
I just put this here to help others decide if weigh sorting is needed.

 

[Petrol & Powder]

There's a lot at play.

Where the void is within the bullet also plays a role. If the void was centered in the rotating mass of the bullet, (yes, I know that's highly unlikely) it would have less effect on the rotational balance of the projectile than if it was off center.

Beyond the rotational stability of the bullet in flight, there is also the effect that mass has on velocity, if all else is equal.
Given the same force (pressure) applied over the same distance (barrel length), a lighter bullet will exit the barrel at a higher velocity than a heavier bullet. Now, that effect will not be as critical as other factors (such as rotational stability and drag) but if the difference in mass is large enough to significantly affect the muzzle velocity, you will see a different trajectory. Increased or decreased time of flight will also effect the amount of time wind and gravity will have on the projectile.

Wind Resistance (aerodynamic drag) IS a big factor. An ill formed base will have a greater effect on accuracy than an ill formed nose. So a void that effects the shape of the base could be critical. (this tends to support Popper's practice of sorting by visual examination)

Whenever you have multiple variables in play, things can get out of hand quickly. Not because we fail to understand the science (we actually have a pretty good grasp on the science) but rather because WHICH variable has the greatest effect becomes important.

 

[358156 hp]

I don't weight bullets. A visual inspection serves my needs just fine. As far as weight goes, my major concern is cutting the sprue too early and tearing divots out of the base.

 

[Dimner]

For each large batch I cast, i first visually sort for defects and then weight sort.
Then I store my bullets in groups of weights +/- 0.2gr. Not because of voids or anything, just piece of mind that those bullets are most likely to be as similar as possible to each other.

Depending on how large the batch is, I find a spectrum of weights +/- 0.4gr at most. Anything out side that range is culled. Normally that last culling is in the single digits.

 

[shuz]

I visually sort my castings for defects and then size, gas check and lube, and then weight sort in .5g increments. I usually find that I have 4 piles of boolits in 100 castings. The majority are 2 piles within 1g. I find this weight sorting gives me piece of mind that I don't have an ultra light boolit that could perhaps spoil a nice group or score.
I find this is easy and fast with a little Hornady pocket sized digital scale.

 

[fiver]

i use weight percentages.[1% total in 3 groups]
but if i had a .6gr weight variance in my 22 casting they'd be finding them all over the place for years to come.

 

[quicksylver]

I don't cast anything smaller than .30 cal in rifle bullets, my method is to cast , initial visuallly sort, label casting session, weight sort to 1 /10 grain
I do so like others for peace of mind and because it gives me a second shot at finding something that I may have missed in the initial visual inspection, I find that any larger variation usually indicates something I have missed like rounded bands/ base, before sizing and lubing I again visually inspect each bullet in a particular weight group, I'm handle them anyways so there is no extra time spent doing so., now that componets are so scarce I want to make sure I am not wasting them and have the most consistant bullets.

 

[popper]

Good comments all. IMHO we pretty much agree weighing is to find dimensionally poor cast bullets. No need to waste components on them. yrs ago discussion was attempts to find voids. Not going to happen, as my numbers above show. I cull after pour and again before GC or PC/lube. Getting pretty picky lately. But from previous non-weighed target results (308 AR) I don't bother, not sure I can shoot well enough to see any difference. Alsoas i showed above, even large variations of weight have NO effect on ballistics. Trying to kill some wives tales.

 

[MW65]

I'm pretty much a visual sorter... gross defects get segregated right at the casting table... others get sorted after all cool and going into the 'to be lubed' bin... if it's a minor wrinkle on the nose, goes into a plinking or recast bin... bases must be great still!

 

[Winelover]

Use to weigh cast, when I first started out. Found little to no weight discrepancies........plus or minus half a grain, at most, in 35 caliber and up. Visual inspection is all I do, now. Loose gas checks will tell the tale, on those passing visual inspection.

 

[Petrol & Powder]

I'm pretty much a visual sorter... gross defects get segregated right at the casting table... others get sorted after all cool and going into the 'to be lubed' bin... if it's a minor wrinkle on the nose, goes into a plinking or recast bin... bases must be great still!

That pretty much sums up my attitude as well.

 

[CZ93X62]

I did a bit of weight-sorting some years back, involving #225438 castings from a one-cavity Ideal mould. I used two alloys--Linotype and 92/6/2. I used a strict scaling regimen (1/2 of 1% of weight increments, 0.2 grains) and found that with both alloys the weight variations were distributed on a bell-shaped curve (who DIDN'T see that coming?). The Lino weight mean was .03 grains lighter than that of the 92/6/2 alloy. 2 rifles have been used during this testing phase--a Ruger #3 with 6X scope and a CZ-527 with 2x-7x glassware. I'll save you some reading, but at three velocity levels using Alliant 2400 powder and Rem #6-1/2 primers, both alloys at these speeds, and using weight-sorted bullets vs. eyeballed bullets.......I could not find a significant difference in grouping at 100 and 200 yards between alloys, scaled vs. eyeballed, or Ruger vs. CZ. All groups ran between 1.3-1.7 MOA, whether at 1600, 1900, or 2350 FPS.

Opinions/Conclusions--I may have run up against the peak accuracy potential of the rifles, the nut behind the stock, or that combination of variables meshing as best they could. One thing I am near-certain of now--scaling of bullets vs. visual inspection (harshly) doesn't matter a bit.

On a related note--casting up the equivalent of a 1# coffee can full of #225438 from a single-cavity mould was an all-day enterprise. I still have what is likely a lifetime supply of these bullets in inventory.

 

[burbank.jung]

I look forward to responses. I believe that different alloys will cast a different weight bullet. Temperature is another factor that can affect weight. I plan to shoot 40cal testloads with possibly a 1% antinomy mix and find an accuracy load with it. With that charge, I will add tin to the alloy in increments to soften the cast bullets. Will this effect accuracy with the same accuracy load from the original alloy? From what I am reading here, no. Am I correct?

 

[Dusty Bannister]

Adding tin does not soften the alloy. It just has less hardening affect than antimony.

 

[Rick]

Adding tin does not soften the alloy. It just has less hardening affect than antimony.

Plus, Sn is self limiting in that after about 4-5% you can gain no more hardness from it. Sn in an Sb alloy should never exceed the percentage Sb.

 

[fiver]

right.
short story.
more tin than antimony allows free tin in the lead and will lead to tin nodules surrounded by pure unalloyed lead.

tin only alloys will soften over time.

 

[Rick]

right.
short story.
more tin than antimony allows free tin in the lead and will lead to tin nodules surrounded by pure unalloyed lead.

tin only alloys will soften over time.

Correct and the higher the percentage of Sn the faster the age softening. That would normally require 4-5% Sn or more. My own experiments with 2% or less Sn showed very little age softening in heat treated bullets. I had bullets heat treated to 30 BHN with 2% Sn and in 10 years they lost 4 BHN, dropped to 26.