Weighing powder charges to improve accuracy

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joeb33050 posted this 09 January 2018

 

 

Weighing powder charges to improve accuracy

 

6.4.5 THE ASTOUNDING POWDER MEASURE TEST! shows the standard deviation of 30 charges thrown with a Lyman 55 measure as .061 grain/IMR4227.

 

The standard deviation of 22 sets of 223 and 22-250 muzzle velocities of 40 and 53 grain bullets with 5.5 to 8.5 grains of Titegroup, is 13.3 fps.

 

 

 

Velocity/grain of the above is:

 

223, 40 gr bullet, 205.1 fps/3 gr powder, (205.1/3) X.061 gr = 4.2 fps = expected standard deviation.

 

223, 53 gr bullet, 172.1 fps/3 gr powder, (172.1/3) X .061 gr = 3.5 fps = expected standard deviation.

 

22-250, 40 gr bullet, 186.9 fps/3 gr powder, (186.9/3) X .061 gr = 3.8 fps = expected standard deviation.

 

22-250, 53 gr bullet, 171.6 fps/3 gr powder, (171.6/3) X .061 gr = 3.5 fps = expected standard deviation.

 

 

 

So, loading Titegroup with a Lyman 55 and shooting, the expected standard deviation of velocity, 3.5-4.2 fps; from powder charge variation alone is about a third of the actual measured standard deviation of velocity, 13.3 fps; which is caused by all the sources of variation; case weight and shooter ability and gun quality and case orientation and cartridge concentricity and bench rest equipment and neck tension and moon phase. Given the myriad descriptions of accuracy determinants, it seems unlikely to me, and Warren Page, that weighing powder charges has much effect on accuracy.

joe b.

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Larry Gibson posted this 09 January 2018

Not quite the way it works joe.

 

Seems you're calculations are going under the assumption that charges weighing exactly the same will give no standard deviation in velocity(?).   It doesn't happen that way.  Load charges that weigh exactly the same still will give a variation in velocity whether its measured by SD or ES.  How much is dependent on many variables we have no control over.  That's what you end up saying at the end. 

 

As to the benefit of weighing charges?  I do some, most I don't.

 

LMG

Concealment is not cover.........

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Westhoff posted this 10 January 2018

I weigh every charge I throw for any of my rifles.

I'm well aware of the fact that it probably doesn't make the rifle feel a bit better....

BUT IT MAKES ME FEEL BETTER !!!

 

Wes

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John Alexander posted this 10 January 2018

Joe,

Unless I misunderstand, your argument is again stronger than your numbers show. 

205 fps/3 grains = 68 fps/1 grain.

68 fps/grain x .06 grain = 4 fps = expected standard deviation from variation in powder weight if variation in powder weight were the only factor -- which it isn't of course.

4 fps is much smaller than the 13.3 fps SD that you found from all the other factors you mentioned. Smaller errors have very little effect on the total error when mixed with much larger errors. The smaller ones are sort of be swallow up the larger errors.

This is a novel approach to showing how unlikely small powder variations affect accuracy.

Of course we shouldn't have to look at the theory. We have had the jacketed benchresters shooting .2" groups with measured charges for a long time now.

Wes has the right attitude. He isn't making the losing argument that weighing powder improves accuracy but it makes him feel good and that is reason enough.

John

 

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Ross Smith posted this 10 January 2018

I agree with John, confidence is a huge factor. 

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BigMan54 posted this 10 January 2018

As A kid growing up we weighed every powder charge for rifle loads, CAST or jacketed. Max revolver loads too. Light handgun loads used a B&M measure.  This ended in 1975 for me. I got my own reloading set up with a LYMAN 55 & a RCBS trickler. I stopped weighing handgun charges & even with max 2400 charges in .357Mag & .44Mag. It DID NOT make a difference in group size. Of course I was in my early 20's, didn't need glasses and had hands as steady as if I was set in concrete for every shot. I was shooting at 25yds at a very well lit indoor range at least 2 nights a week, 200+ rounds per session. I sometimes got groups down to 1 1/2" or even 1 1/4". I used cast exclusively with  the standard loads for BULLSEYE, UNIQUE & 2400.  When the RCBS Little Dandy came out a year or 2 later I switched to it for all my handgun loading. I still use it today for small batch loading of 50-100 rounds. I don't weigh charges by " hand " anymore as I've had a LYMAN 1200 Auto Powder Measure/Scale since they came out. At the same time i was doing some sorta bench rest shooting, dumping ball powder charges into 222Rem & 6mmRem. I detected very little difference between H322, BL-C2 & weighed charges of IMR3031 or IMR4198. Of course they were not bench rest rifles, just good triggers & glass bedding. And I never let them cool enough between strings.  

Push the button, dump the charge into the case, put the pan back on the scale & push the button again. Seat a bullet in the case & the next charge is waiting in the pan. WOW, I think I can load rifle rounds faster then I can shoot'em out of a single shot at the range. 

So as far as there being a difference for weighed/dumped charges it has once again become a moot point for me as far as rifle loads go. I don't think there is any difference for handgun, and I proved that to myself 40yrs ago.

Long time Caster/Reloader, Getting back into it after almost 10yrs. Life Member NRA 40+yrs, Life S.A.S.S. #375. Does this mean a description of me as a fumble-fingered knuckle-draggin' baboon. I also drool in my sleep. I firmly believe that true happiness is a warm gun.

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joeb33050 posted this 10 January 2018

Joe,

Unless I misunderstand, your argument is again stronger than your numbers show. 

205 fps/3 grains = 68 fps/1 grain.

68 fps/grain x .06 grain = 4 fps = expected standard deviation from variation in powder weight if variation in powder weight were the only factor -- which it isn't of course.

4 fps is much smaller than the 13.3 fps SD that you found from all the other factors you mentioned. Smaller errors have very little effect on the total error when mixed with much larger errors. The smaller ones are sort of be swallow up the larger errors.

This is a novel approach to showing how unlikely small powder variations affect accuracy.

Of course we shouldn't have to look at the theory. We have had the jacketed benchresters shooting .2" groups with measured charges for a long time now.

Wes has the right attitude. He isn't making the losing argument that weighing powder improves accuracy but it makes him feel good and that is reason enough.

John

 Thanks, John-I fixed it.

joe b.

 

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