Weight variance in monometal bullets

[cornstalker]

What factors would contribute to weight variance in machined bullets?

The numbers I came up with are so small that they are of no consequence, so please do not misunderstand my intent here. I just honestly expected precision-machined bullets to weigh the same. What would contribute to them varying a tiny amount in weight, and how could it do so without changing the dimensions of the bullet unless it was in the hollow point cavity? I am not knowledgeable about machining processes and reasonably expected variances.

I do not have a scale that goes down to the hundredth of a grain, only tenths. I weighed 15 of each of the following on a Dillon and an RCBS digital scale. The two scales yielded the same results.
.308"
181 Hammer Hunter- .2 grains spread
180 Sierra Tipped GameKing .3 grains spread
190 Barnes LRX .5 grains spread.

I was really surprised to see the Barnes have a wider spread than a cup and core bullet.

 

[Hand Skills]

To the best of my knowledge, Barnes are cast and not machined, which would explain the larger variance in their bullets.

 

[fordy]

Gday cornstalker
I'll 2nd handskills plus add this

Depending on the company that supplies the raw material ( foundry) you have a certain spec that the manufacturer will have
Basically some have tighter tolerances than others
Then you add the bullet company that require even tighter tolerances of those supplied

Now we also need to add the "cookie mix " of that alloy into the various companies but that's not only with monos & probably delving deeper than your original question revolves around
So I'll stop there

Cheers

 

[dfanonymous]

If it's machined, then it's a matter of allowable tolerance. Casting the bullet is a matter of saving on material waste I would assume. Especially for a mass produced item.

I myself thought Barnes were swagged

 

[fordy]

If it's machined, then it's a matter of allowable tolerance. Casting the bullet is a matter of saving on material waste I would assume. Especially for a mass produced item.

I myself thought Barnes were swagged

Gday dfanonymous
swagged or cast hmmm yes vastly different

I would think I better get my words correct
Yes muppet moment from me thanks for pick up
Cheers

 

[Koda_]

I just honestly expected precision-machined bullets to weigh the same. What would contribute to them varying a tiny amount in weight, and how could it do so without changing the dimensions of the bullet unless it was in the hollow point cavity? I am not knowledgeable about machining processes and reasonably expected variances.

Tolerances on machined parts largely comes down to tool wear and how often the machinist replaces tooling.
Variances in material metallurgy tolerances, machine calibration/wear can also come into play. Then there is always the "operator error" can be minor to catastrophic regardless the best tooling, machines and materials.

In even the best machining there is always a tolerance, nothing will ever measure or weigh exactly the same, as long as the variance is within acceptable/usable limits its fine and modern machining technology has certainly made this virtually a non issue in bullet production. I do think this is why lathe turned bullets are more accurate/consistent than swaged monolithic bullets. That said I still mic one bullet in every box I order.

 

[Weaver93]

It would be interest to know how much difference you would see based on material lot or machining processes, but I think you will need more resolution in the scale to see things more realistically. I'm probably oversimplifying this, but a scale that measures to .1 grain might see two bullets that are .01 grain apart as .1 apart. In theory .15 grain is rounded up and .14 is rounded down.

 

[Koda_]

It would be interest to know how much difference you would see based on material lot or machining processes, but I think you will need more resolution in the scale to see things more realistically. I'm probably oversimplifying this, but a scale that measures to .1 grain might see two bullets that are .01 grain apart as .1 apart. In theory .15 grain is rounded up and .14 is rounded down.

Production lots are the only way to track machining variations that I know of, but I dont think bullet manufacturers ship inventory by lot codes. We could in theory get a production lot of cnc turned bullets that weight .1gn different with even the best quality machining, add the rounding issue you mentioned it could even vary by .2gn.

I have an order of Nosler partitions I weigh sorted, the spread was so bad I never used them.

Weighing monos, I found Barnes vary worse than cnc turned bullets, not in an unusable sense (I like Barnes bullets) but I think the consistency of machined bullets aids in their accuracy so I switched brands. As I mentioned, I still mic bullet diameters only cause an out of spec bullet can cause pressure spike, again Barnes had the largest variation even in the same box.

 

[Coyote Shadow Tracker]

What factors would contribute to weight variance in machined bullets?

The numbers I came up with are so small that they are of no consequence, so please do not misunderstand my intent here. I just honestly expected precision-machined bullets to weigh the same. What would contribute to them varying a tiny amount in weight, and how could it do so without changing the dimensions of the bullet unless it was in the hollow point cavity? I am not knowledgeable about machining processes and reasonably expected variances.

I do not have a scale that goes down to the hundredth of a grain, only tenths. I weighed 15 of each of the following on a Dillon and an RCBS digital scale. The two scales yielded the same results.
.308"
181 Hammer Hunter- .2 grains spread
180 Sierra Tipped GameKing .3 grains spread
190 Barnes LRX .5 grains spread.

I was really surprised to see the Barnes have a wider spread than a cup and core bullet.

To sort these bullets by weight you to have a very accurate Lab scale at least to 1/100 of a grain. Too much variance with 1/10 gr on a RCBS or Dillon.
Also if they are hollow tip/ OTM bullets make sure they are clean. I have done weight sorting before and not worth it, I would wet tumble with water and cleaning solution then dry for several days and weigh.
Good match bullets are different than hunting bullets

 

[cornstalker]

The juice doesn't seem worth the squeeze in regards to buying a lab scale. I will call out that weighing on one scale then the other right after and getting the same results across 45 bullets should yield accuracy to within .1 of a grain for the Hammers, factoring in the potential rounding error.

Not worth pursuing further. Just trying to wrap my head around there being a variance that would show up at all on my scale on an item that has been precisely machined to the .001". Or possibly even .0001".

 

[Koda_]

The juice doesn't seem worth the squeeze in regards to buying a lab scale. I will call out that weighing on one scale then the other right after and getting the same results across 45 bullets should yield accuracy to within .1 of a grain for the Hammers, factoring in the potential rounding error.

Not worth pursuing further. Just trying to wrap my head around there being a variance that would show up at all on my scale on an item that has been precisely machined to the .001". Or possibly even .0001".

Because your using a scale with only .1gn of resolution. And those scales are often not repeatable. Weigh a bullet, leave it on the pad then press the pad and release and sometimes it will change by .1...

 

[cornstalker]

Great idea. I will try it.

I have done that with powder charges and haven't noticed a change so far.

 

[cornstalker]

But that is less than half the weight, so the same percentage of variance could slip through the rounding error.

 

[Koda_]

Great idea. I will try it.

I have done that with powder charges and haven't noticed a change so far.

It might depend on which brand you have? Mine is horrible for repeatability. I have a cheap Frankford Arsenal digital scale.

But that is less than half the weight, so the same percentage could slip through the rounding error.

All of the "affordable" digital scales Ive seen have a tolerance of +/- .1gn, so the rounding error could stack up with repeatability issues up to .2gn. IMO there's no way a scale with a tolerance of +/-.1gn can be used to weight cnc machined bullets accurately.

When I started handloading I got the Frankford Arsenal scale (iirc 40 bucks), it took me a while to learn it was holding me back. Huge standard deviations and ES. Ive heard that temp changes can affect readings, using it under flourescent lights/electrical interference. I started cluing in on whats going on, did some tests where I put a weight on it and wrote that down, then came back 10 minutes later and half the time it would be another .1gn different. Same results measuring the same thing the next day. Then Id press on it and let go and it wouldn't return to the same value. To me, that right there meant I could never trust it.
I bought an analog scale and haven't looked back (though I discovered "parallax" is what affects analog scales but no where near off like cheap digital scales)

Id be curious what you find testing repeatability in your digital scale.