Home Forums Reloading Big Game Rifles Weigh and Anneal

Meh. Do you really think everybody else gets similar results, with every powder out there? You're going to pretend that a guy dispensing 3031 with a Uniflow will get the same results?
Seriously, you miss the forest because of all the trees.

Do you really think everybody else gets similar results, with every powder out there?

Assume that you are measuring powder down to 1/10th of a granule, and that variation in bullet weight, neck tension, case capacity, etc. are giving you a standard deviation of 30 FPS. So you switch from measuring down to 1/10th of a granule to using my powder measure. Here are the actual numbers:

223/5.56, Varget. The standard deviation of 30 FPS becomes 31.95 FPS as previously shown.

223/5.56, ball powder. SD of the powder measure is .041 grains. The standard deviation of 30 FPS becomes 30.28 FPS.

308, Varget. The standard deviation of 30 FPS becomes 30.67 FPS.

308, ball powder. The standard deviation of 30 FPS becomes 30.04 FPS.

I've given you all the necessary steps, so you can make the same calculation for other cartridges if you like.

I got a pretty good powder measure, some kind of RCBS .Using stick type powder I never trust it. Nothing to do with the powder measure but rather the way the kernals fall into the powder hopper. You can fill the hopper and then bump it a couple time and make the weight change. Not for me, I weight every load with stick powder. Ball powder measure's much better and once I get the thing set I throw 10 loads and weight them. They need to come out real close to ten time's one charge or I don't just throw them. Flake powder is in it's own world. Only reason to weight it is to set the measure! I don't weight handgun loads other than to set the powder measure.

I weigh ten throws together to get a good estimate of the mean and that's what I designate as the particular load.

Run the math on your own setup, and argue with that.

Which means you don't know zip about the actual variation.

Sure, you have some loads that shoot great that way. That's not what denton claimed though. "practically all applications" was his wording, and you've claimed similar in the past yourself.

You need to get out and shoot more, and forget about the math so much.

The math isn't very painful.

The basic concept is that variation does not simply add. If you're shooting 6" groups offhand at 50 yards with a perfect rifle, switching to one that does 2" groups at 50 yards (an SKS!!) will NOT make your groups 8". It will make them more like 6.3". If there is one large source of variation in the chain, it will almost completely determine the total variation. That is why fiddling with small sources of variation is pointless. You have to find the big sources if you want to make any progress.

One good measure of variation is standard deviation. The higher your standard deviation, the more spread out your data are (and the higher your "extreme spread" generally will be). Standard deviations add by the square root of the sum of the squares. It sounds forbidding, but it's really not so bad if you work through it step by step.

Take the case of the 5.56/223. In a small case like that, small changes in the powder charge are more important than they are in a large case like the 30-06. So this small cartridge is sort of an "acid test". The changes in larger cartridges will be less important.

With a stick powder like Varget, my powder measure throws charges with a standard deviation of .11 grains. In the 223, near normal loads, a grain of powder is about 100 FPS in MV. So a standard deviation of .11 grains in charge produces .11 x 100 = 11 FPS standard deviation in muzzle velocity.

It's not too hard to get the standard deviation of 5.56/223 handloads down into single digits, but commercial ammunition tends to run at about 30 FPS standard deviation of muzzle velocity.

So for purposes of illustration, assume that a handloader is making 5.56/223 ammunition with a standard deviation of 30 FPS in muzzle velocity. As part of the process, the handloader is using a lab grade scale, and is creating powder charges down to the last 1/10 of a granule of powder, essentially perfect loads.

OK... starting from perfectly measured loads, and a 30 FPS standard deviation in MV, what would be the effect of switching to my Lee Perfect Powder Measure that has a standard deviation of .11 grains?

First, we square the two standard deviations involved:

30^2 = 900

11^2 = 121

Now we add the two squared numbers: 900 + 121 = 1021.

Now we take the square root of the sum of the two squared numbers: square root 1021 = 31.95.

So going from a perfect measurement of powder to my $27 powder measure increases the standard deviation of muzzle velocity from 30 FPS to 31.95 FPS.

QED

I hope you're not sorry you asked!