Bullet weight variations

[tangolima]

What's the expected weight variation of non-match grade varmint bullets?

I bought 400 6mm varmint bullets at 18 cents a round. Speer 100gr spbt. Out of curiosity I weighted 20 random samples and got mean 99.93gr stdev 0.20gr. So I expected 99.93+/-0.6 gr, or +/-0.6%. Not too bad I suppose.

I went ahead and sorted the bullets into 3 buckets; <99.73gr (~30%), 99.73-100.13gr(~50%), >100.13gr(~20%). Down the road, I will do running sort as I load for all calibers, either 2 buckets(3 sigmas each) or 3 buckets (2 sigmas each) depending on number of bullets I have. Hopefully it will tighten things a bit more. Will see.

-TL



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[44 AMP]

100gr 6mm bullets seem pretty heavy to me. Might want to check with Speer to see if they are actually varmint bullets or controlled expansion bullets intended for larger game (like deer).

Weight consistency can matter, but when you're talking about less than a couple of grains, the question becomes, "Will your gun even notice the difference?"

Lots of guns, won't.

[tangolima]

You are right. It is medium game bullet.

The bullet weight spreads from 99.3 - 100.5gr. As per GRT, the corresponding MV are 2866 and 2858fps respectively. MV extreme spread measured about 35fps. Bullet sorting may help reduce the spread to 30fps ish, I hope. Not much indeed. But every bit helps.

-TL

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[BringEnoughGun]

I have also found varying weights in new batches of bullets. I asked a bullet maker at Sierra Bullets several years ago, what the max variation should be. He looked me straight in the eye and said there will not be any variation in our bullets, they are all the same weight!
I have not found this to be true, thus the question. But I didn't want to ruffle the old boy's feathers.
I have 3 digital scales, and on given days they may or may not read the same weight. I have also sorted them out by weights as you have, and then gone back and weighed them the next day on the same scale and found many weighed differently.
I guess it is not a perfect world!! For those of us wanting perfection, it can be maddening.
Note: I'm not a gold medal competitor, or long range sniper, but have not found the difference in bullet weights to be detectible...

[tangolima]

He who told you no weight variation had no business doing engineering. Maybe he truly didn't.

Anything digital has finite resolution, or least significant bit (LSB). For common digital scale, LSB is 10mg (they are all naturally metric), or rounded to 0.2gr. For a constant weight of 40.12gr for example, the indicated weight could ditter between 40.0 and 40.2gr, or between 40.2 and 40.4gr. That may be why you saw different results. To be honest, such resolution is too coarse for load development, especially pistol loads.

My scale is jeweller type. At the expense of max weight, it has LSB of 1mg, or 0.02gr. The same 40.12gr weight, it will show up as 40.10 to 40.12 or 40.12 to 40.14. Still dittering but much better.

Beam balance better? That's different discussion. I tried one briefly and went back to digital.

-TL

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[44 AMP]

A good balance beam scale, graduated in grains usually reads down to .1gr, which means your accuracy is essentially .05gr rounding up or down to the nearest .1gr.

Consider this, 7000 gr in a pound, so .1gr is 1/70,000 of a pound. Nice to have that degree of precision in measuring, but what percentage of firearms are actually going to have a measurable difference in anything related to velocity or accuracy from such a small difference??

As one of my friends puts it, "if it doesn't help me put elk in my freezer with my Savage 99 .300, its not worth bothering with."

Put another way, the tips, tricks, and attention to minute details a handloader can do, only have value if the guns you're shooting benefit from them, and that is something as individual as each individual gun, and shooter and desired purpose.

[tangolima]

There is nothing wrong with extra precision if it doesn't cost anything extra.

0.1gr is certainly insignificant compared to 1lb. But we are measuring something much lighter. 0.1gr in 40gr bullet is 0.25%. 0.1gr in 10gr pistol powder charge is 1%. I have loaded .25acp down to 2gr of powder. 0.1gr means quite a bit more.

Anyway, I agree tight MV SD doesn't automatically lead to tight group. But it never hurts.

-TL

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[noylj]

Like many, I have weighed and sorted bullets.
After testing 500 sorted bullets, the most accurate were mixed weight lots. Since they can't be best, though they were in multiple groups, a 2 grain variation made no difference out to 100 yards (no access to longer range).
Why not sort them and mix them and answer your own question?

[tangolima]

Originally Posted by noylj

Like many, I have weighed and sorted bullets.
After testing 500 sorted bullets, the most accurate were mixed weight lots. Since they can't be best, though they were in multiple groups, a 2 grain variation made no difference out to 100 yards (no access to longer range).
Why not sort them and mix them and answer your own question?

I will. I don't expect to see significant improvement though, very minute even with everything works right. But I don't see any reason consistency will make things worse, otherwise everybody will be purposely mixing bullets of different weights or even types to have better groups.

-TL

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[georgehwbush]

yeah two thoughts; 1. i also doubt that 100gr 6mm is a varmint construction, they are normally medium game or target.
2. as per .1 .2 gr powder .1 .2 gr bullet... that probably wont show up inside 300yds for most shooters, but it definitely will at long range, say outside half a mile (880yds) and yes 1000yds is well within the reach of a 6mm bullet of higher bc pushed over 2900 ft/s

[Shadow9mm]

I weight sort my bulk bullets. I weed out the stragglers at the extremes and keep those for fouling shots. Last 1000, 600 or so were in the 55.4-55.5 range. Keep those as my "A" grade target bullets. Rest get used as close range training.

[totaldla]

Assuming the bullet fits the bore, the base accuracy of a bullet is how closely the rotational center of gravity is to the physical center of the bullet. If there is an off-center void in the lead core, the imbalance will cause the bullet to move laterally with each revolution after it leaves the bore.

Since there is natural variation in the manufacturing process, how do you know what a reasonable variation should be?

If you're shooting 3" groups at 1000yds, you can't tolerate much dispersion, so you justify $3/ea bullets. But if you're happy with 3" @200yds?

I'm not knocking weighing bullets - I just don't understand the benefit (kindof like uniforming primer pockets).

[totaldla]

Originally Posted by 44 AMP

A good balance beam scale, graduated in grains usually reads down to .1gr, which means your accuracy is essentially .05gr rounding up or down to the nearest .1gr.

.

If a scale is graduated to 1/10 grain, unless you've tested otherwise, the accuracy would be +/- 1/10 grain - or 2/10 grain.

[tangolima]

Originally Posted by Shadow9mm

I weight sort my bulk bullets. I weed out the stragglers at the extremes and keep those for fouling shots. Last 1000, 600 or so were in the 55.4-55.5 range. Keep those as my "A" grade target bullets. Rest get used as close range training.

Good idea. I'm adopting that with modifications. Mean +/- 1 sigma is grade A. 2 sigmas above / below that are grade Bl and Bh. A, Bl, Bh are good. Anything else is range fodders.

-TL

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[tangolima]

Originally Posted by totaldla

Assuming the bullet fits the bore, the base accuracy of a bullet is how closely the rotational center of gravity is to the physical center of the bullet. If there is an off-center void in the lead core, the imbalance will cause the bullet to move laterally with each revolution after it leaves the bore.



Since there is natural variation in the manufacturing process, how do you know what a reasonable variation should be?



If you're shooting 3" groups at 1000yds, you can't tolerate much dispersion, so you justify $3/ea bullets. But if you're happy with 3" @200yds?



I'm not knocking weighing bullets - I just don't understand the benefit (kindof like uniforming primer pockets).

I think +/- 0.5% is pretty good enough. That probably affects mv by +/- 0.3%.

3" at 200yd is not bad. But if I can shrink it further I wouldn't mind doing it. Beyond 200yd, my game changes. It is not about the group size anymore. But rather the hit rate on a target, say a 8x11 paper. In a way wind call accuracy becomes more and more critical.

-TL

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[44 AMP]

If a scale is graduated to 1/10 grain, unless you've tested otherwise, the accuracy would be +/- 1/10 grain - or 2/10 grain.

Apologies for the confusion, the scale's accuracy in +/- .1. Your (and my) accuracy reading the scale is about half that. About, not exact. One can usually see if the indicator line is on, or between the .1 lines, and if it appears closer to one mark than the other.

[tangolima]

Originally Posted by 44 AMP

Apologies for the confusion, the scale's accuracy in +/- .1. Your (and my) accuracy reading the scale is about half that. About, not exact. One can usually see if the indicator line is on, or between the .1 lines, and if it appears closer to one mark than the other.

Actually we can eyeball pretty accurately down to 1/4 of a grid, or 0.02-0.03gr. It is as good as a jeweler digital scale. Nothing wrong except the speed. Each time I touch the dial, I will need to wait till it settles.

-TL

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[cdoc42]

Is a change in the base to ogive any more significant than the difference in weight? I have 500 rounds of .277 Remington 130gr PSP that I bought back in the 80s when the bulk price was attractive from Midway USA. I could not get a satisfactory group no matter what I did, which is still why I have them. For the heck of it, I measured 100 bullets from the base to the ogive with a .277 comparator and found the bullets ranged from 0.538 to 0.570 inches. In those 100 rounds, any number of them may have been the same measurement, i.e., 3 would measure 0.538 while another 6 would be 0.570 or anything in between. I "double-checked" with a box of Hornady .277 ELD-X and only measured 10 bullets and they ranged from 0.714 to 0.715".

I attributed the wide difference in measurement of those Remington bullets to explain my inability to get a good group, and I figured they were a good price because they may have been factory "seconds."

[tangolima]

Originally Posted by cdoc42

Is a change in the base to ogive any more significant than the difference in weight? I have 500 rounds of .277 Remington 130gr PSP that I bought back in the 80s when the bulk price was attractive from Midway USA. I could not get a satisfactory group no matter what I did, which is still why I have them. For the heck of it, I measured 100 bullets from the base to the ogive with a .277 comparator and found the bullets ranged from 0.538 to 0.570 inches. In those 100 rounds, any number of them may have been the same measurement, i.e., 3 would measure 0.538 while another 6 would be 0.570 or anything in between. I "double-checked" with a box of Hornady .277 ELD-X and only measured 10 bullets and they ranged from 0.714 to 0.715".

I attributed the wide difference in measurement of those Remington bullets to explain my inability to get a good group, and I figured they were a good price because they may have been factory "seconds."

Good point. I can sort that too.

-TL

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[Unclenick]

Just for perspective, thirty caliber military bullets (including the match M1 Type bullets) have their weight expressed as a maximum with a minus three-grain tolerance. Indeed, a lot of cast bullet experts have stated for years that three grains don't matter. If three grains is, say, 2%, you get a 2% increase in ballistic coefficient and about a 0.5% reduction in velocity. They don't compensate well, but at least it's in the right direction and helps hold the errors down.

In general, I expect it to be more important to determine if a bullet is balanced than if it has an exact matching weight. Ogive difference will affect the ballistic coefficient some, and you can use the calculators on Geoffrey Kolbe's site to get some idea how much.

[tangolima]

Ogive profile affects bullet jump. It is a good parameter to tighten, I think.

-TL

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[Shadow9mm]

Presuming they are from the same lot, what would the expected/acceptable variance be using a comparitor to measure from the base of the bullet to a point on the ogive?

[Unclenick]

I don't know exactly. When I measured Sierra 150-grain 0.308" MatchKings from base to comparator intercept with the ogive, I got an extreme spread of 0.008", and those bullets shot fine.

[cdoc42]

In the example I gave, the Remington spread was 0.032," compared to ELD-X bullets = 0.001"

[georgehwbush]

cdoc42; yes .032 diff will indeed cause poi shifts. and if you loaded to overall length rather than base to ogive length your harmonics also change, in effect you changed the jump to lands. by seating that way.