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Yesterday @BlackJack asked a very pertinent question in one of my posts,

"...i am curious if those 20 rounds gave you any different results than the ones loaded for precision, and if so, how much of a difference was it? Basically, by just looking at this limited number of loads, does it look like you are seeing any real justification for spending the extra time and effort in "loading for precision"?"

Since I couldn't answer that definitively due to lack of viable data, this morning I loaded 50 Lapua cases using the Uniflow powder measure. I weighed each charge thrown and included the weight with the velocity data I will get shortly when I shoot the rounds.

My target load was 23.1 gr of IMR 8208 XBR. I tried to be as consistent with the powder throw as possible and I measured each on with the Frankford Intellidropper digital scale and powder dispenser.

The procedure was throw a charge, dump the charge carefully into the scale pan and "enthusiastically" tap the case about 3 times to be sure all the powder dumped. Then the weight was recorded and then the powder was put back in the case. Here's the way it turned out, stats are at the top. And do remember, this is for IMR 8208 XBR and a specific target charge of 23.1 gr; other powders may give different results.



So, does it matter? I think to answer that we have to clarify "who" it would or would not matter to. I know, I know, I ended a sentence with a proposition :tongue:

I would expect that under 200 yards the approximate worst case variation of +/-0.2 gr from the average would be negligible. For example, from my BSF 14.5" "pistol" barrel, and according to QuickLoad, the target charge of 23.1 gr produces 2593 fps, 0.2 gr higher produces 2616 fps, and 0.2 gr less produces 2570 fps. The variation in impact, due to velocity variation alone at 200 yards would be +/-0.12" from the POA.

At 500 yards the POI shift due to the +/-0.2 gr variation would produce a POI shift due to velocity variation alone, of +/-1.5" from the POA. That 1.5" sounds like a lot, but remember at 500 yards 1 MOA is right at 5" (4.78"). That 1.5" at 500 yards is 0.28 MOA, so even at 500 yards that variation is less than a third of an MOA - whether that's significant or not.....

Plus, those numbers are for the worst case, and the +/-0.2 gr is a wee bit high on top of that. And, by my calculations, nearly 80% of these charge weights varied by 0.1 gr or less. So using worst case numbers doesn't really tell the truth exactly when nearly 80% of the time the charge variation is going to be far less than worst case.

Shortly, I'll be heading to the range to shoot an measure the 50 "Uniflow" charges. I expect the velocity variation to be far more than indicated by velocity variation alone. For example, according to the Quickload velocities, I should see a variation of 46 fps, i.e. ES, but I get that from precisely loaded charges. It's gonna be interesting to see the results!
 
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OK, let's go do this!
 
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