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Weight Variation in 6mm 105’s

Rat Rifle

Since We discussed the significance of 1 kernel of powder, My thoughts went to weight difference in sorting bullets. I just finished sorting 500 bullets that I wouldn’t have bought, except for the shortage. Except for light and heavy outliers, the majority fell within .5 grains. I can weight to .02 grn, plus or minus scale variation. This batch of bullets had more variation than I am used to, I was hard pressed to get 50 all the same. I’m not used to that.

My question is, how many .02’s is enough to show a difference at 1,000yds on paper, all other variables excluded ? 6mm, 105 + or - class bullets.

Thanks…RR
 
I don't have the time or money to shoot at 1000, and maybe someone with fancy software can give you a good theoretical answer. Better yet someone with practical experience may check in.
But until they do I'll give you my free opinion because I like to test this sort of thing here at home. Shooting at even 50 yards there's a measurable change in a weight difference of just one half of one percent of the bullet's weight when bullet weights are 65 and below. I would think that with a heavier bullet the effect is less and by the time you get to 105s it might be just one percent. And when they're up around 165 it's around 1.5 percent in my experience.

But the only way to know what is really going to happen is by trying the bullets you have in your gun.
Embrace the journey.
 

bulet weight variation

In a 223 rifle shooting 77 gr SMK bullets how much variation in bullet weight is acceptable ? weighted a bunch and the range was from 76.9, 77.1 and 77.2 grains. Is a 3 grain weight difference enough to cause flyers or other problems ? I am shooting 300 yd F-class matches.
forum.accurateshooter.com
 
Ccrider, Your advice prompted Me do do further searches, which answered some questions for Me. One of My problems is “fliers”. I shoot 4 into less than 1 inch, at 600yds, and a flier takes one out to 2” or more. I don’t think My fliers are coming from 1 kernel of powder, or from a bullet weight difference.02 grain. Although I do weigh and sort to that tolerance.

I feel that My weight sorting method is the best I can do with what I have.

I think the fliers are coming from something else. Like base to ojive, or internal case volume.

Of course they could always be coming from “ME” :(
 
There are at least a couple simple things you can try to get a handle on whether weight sorting bullets will have a noticeable effect. One would simply be to sort some bullets by weight, pick out at least 5 (each) from the lowest and highest weight range. Load them up with an identical powder charge weight, then shoot them over a chronograph and determine average velocity for the lowest and highest weight groups. That will tell you whether the greatest extreme weight variance within your Lot# of bullets is actually causing detectable velocity variance.

The second is a theoretical exercise, but points at the same answer. We can use the working assumption that two bullets of slightly different weight loaded with the same powder charge (i.e. same pressure) should have different velocity, but the same kinetic energy. The formula for kinetic energy is (1/2)MV*2 (one half mass times velocity squared). You can use this formula to estimate the effect of bullet weight on velocity by setting up an equation for two bullets of slightly different weight, but having the same kinetic energy. The final equation setup is 1/2M1V1*2 = 1/2M2V2*2.

Multiply one bullet weight times its average [measured] velocity squared (i.e. M1 x V1 squared); the 1/2 term is on both sides of the equation, and so disappears). Divide that value by the second bullet weight (M2), and take the square root to estimate velocity (V2) for the second bullet. This is an easy method to estimate the velocity for a given charge weight for two bullets of different weight. As an example, let's say you have a 200.0 gr bullet, and one that is 200.5 gr. The velocity for the 200.0 gr bullet is 2650 fps (M1 and V1). What would be predicted velocity at an equal charge weight for the 200.5 gr (M2) bullet?

M1V1*2 = M2V2*2
(200.0 gr)(2650 fps)*2 = (200.5 gr)(V2)*2 >>> solve for (V2)*2, then take the square root to find V2

The velocity estimate comes out to be 2646.7 fps, or 3.3 fps slower for the heavier bullet. In other words, the bullet weight variance needs to be substantial before it causes a significant change in velocity. My gut feeling would be that your fliers are due to some cause other than a difference in weight affecting velocity. As you noted, differences having no direct effect on overall weight such as bullet ogive, meplat, concentricity, etc., are also likely culprits for the fliers, and it is unlikely that weight-sorting your bullets will have any effect if the fliers are caused by differences other than weight. Nonetheless, you can certainly test for velocity variance, if for no other reason than peace of mind. If velocity variance due to bullet weight is not the answer, you could try sorting bullets by OAL or BTO, pointing them, or even using a tool that spins the bullets to look for concentricity issues. Although such tools are not common, they do exist. Alternatively, trying a 6 mm bullet from a different manufacturer might be the easiest thing to do.
 
Thanks Ned for the great response. Being weak in math, I prefer Your first suggestion. But I very much appreciate Your mathematical explanation. I think it’s telling Me .02grn, or even if there is error out to .04 or .06grn, I will never see the difference at 1,000, or even 600 yards, on paper, with My 105grn bullets. Considering weight difference alone. I will continue sorting as I have to eliminate high and low outliers and arrange in equal groups.

It’s easy enough to measure bullet length. But to measure bullet Base to Ojive, I’m going to have to step up and spend some more money, because I’m not confident in the accuracy of My current method.

Except for Boating, this is the most expensive Hobby I ever had, and it’s catching up fast.

Thanks for the great help Ned…RR
 
Trying another bullet, or bullet manufacturer, or powder, would be easier and possibly more productive. Even with the best of technique it is still up to the rifle to decide if the load is a winner.

I'm still new to this and in the beginning I'd buy some brand name bullets and powder and beat that horse to death. Now I have enough variety to switch and try something different if the first combo doesn't make the grade.
 
Last edited:
Rat Rifle said:
Ccrider, Your advice prompted Me do do further searches, which answered some questions for Me. One of My problems is “fliers”. I shoot 4 into less than 1 inch, at 600yds, and a flier takes one out to 2” or more. I don’t think My fliers are coming from 1 kernel of powder, or from a bullet weight difference.02 grain. Although I do weigh and sort to that tolerance.

I feel that My weight sorting method is the best I can do with what I have.

I think the fliers are coming from something else. Like base to ojive, or internal case volume.

Of course they could always be coming from “ME” :(
Click to expand...
20% fliers ? Sounds like me except for the 1 inch 4 shot groups at 600 yards.
Rat Rifle said:
Since We discussed the significance of 1 kernel of powder, My thoughts went to weight difference in sorting bullets. I just finished sorting 500 bullets that I wouldn’t have bought, except for the shortage. Except for light and heavy outliers, the majority fell within .5 grains. I can weight to .02 grn, plus or minus scale variation. This batch of bullets had more variation than I am used to, I was hard pressed to get 50 all the same. I’m not used to that.

My question is, how many .02’s is enough to show a difference at 1,000yds on paper, all other variables excluded ? 6mm, 105 + or - class bullets.

Thanks…RR
Click to expand...
What bullet are we talking about.
 
Bullets You would use for a door stop ;). But I’m grateful to have them or I wouldn’t be shooting this weekend. Because I am grateful, I will not mention brands, they are production bullets. But even top custom bullets have a weight range variation and outliers. It’s just not as much. The brand I just finished weighing ranged from 104.72grns to 105.38grns. Ug. If I didn’t weight sort, I wouldn’t know this. The 105.38 could end up with 4 104.72’s and could (would?) have a POI different from the other 4 at 1,000yds.

The way I currently load, I load 10 for a Light Gun relay, cases weight sorted to .02 +/-grns (if possible), bullets within.02grns, and powder to .02grns. I know that case weight does not equal case volume, but I’m not going there.

FROM WHAT WE HAVE LEARNED, I THINK MY FLYERS ARE NOT COMING FROM BULLET WEIGHT VARIATION OR 1 KERNEL OF POWDER ???

As far as the 20%, a better example, I shot 4 Heavy Gun targets, and was 18th out of 28. If 4 fliers had been in the outer edge of their group, I would have been in the top 4 or 5. I know, so what you wouldn’t have been in the wood anyway LOL.

The subject is bullet weight consistency and I have drifted to fliers. Fliers can come from almost anything, an I know they can certainly come from Me. These questions come up at every match. Walk down the line of targets, “Look at that, 4 took out the x, what happened to that one 2 1/2”s out?

Thanks All for Your Help…RR
 
There is also a debate that Erik Cortina mentions regarding neck sizing only versus full length sizing your brass. Which do you do....?
 
I FL size every time.

But the subject is bullet weight/variation.

Oh, look at the bottom of the page! This has been beat to death before :)
 
For what it's worth, small weight variations are partially compensated for by the slightly increased pressure caused by the heavier ones. At what point it starts to matter is a subjective thing.

One thing to know is that BC is proportional to weight. a 106 grain bullet will have a 0.9% higher BC than a 105 grain bullet, all else equal. That's small enough to get lost in the noise, as is the difference in velocity between the two (the heavier one will also have a slightly lower velocity, so that cancels out the extra BC to a degree). I don't worry about small weight variations for that reason. There's always the chance that you'll find a really bad bullet in a box, but I don't have time to sort them all by weight so I just live dangerously.
 
CNC, You just reminded Me. Did You see where Erik shot that less than 1” group at 1,000yds, and the last one took it out to 1.3”s ? He and Speedy did quite a cretek on it. Maybe someone can post it ?
 
damoncali, what’s the wait time on Your bullets ?

It may not matter for Me next season if I can’t get powder or primers :(
 
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