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Weighing Powder - How precise is good enough?

 
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  #8  
Old 08-05-2011, 12:43 PM
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Re: Weighing Powder - How precise is good enough?

The level of precision that you care about should be measured (by you, not your scale) in percent, not grains (or tenths of grains, even).

.1 grain is only 1/10% difference in my 300RUM (using a 96.5g charge)

.1 grain is 2% difference in my .40 S&W (using a 4.7g charge)

Whether or not that level of precision is necessary for *your* load is an exercise for the reader. But, just some food for thought....

--Ben

P.S. Jeff, that picture is hilarious. My dad puts ear muffs on his lab when they're in the wood shop together. The lab doesn't care a bit......pretty funny to see him wandering around or laying in the shop with his big red shooting ear muffs on.
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  #9  
Old 08-05-2011, 01:17 PM
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Re: Weighing Powder - How precise is good enough?

It is also a matter of the load itself.
When loaded to extreme pressures, powders burn faster, the pressure peak narrows, and barrel timing becomes more or less constant, with only little things like air density(that piston of air in the bore) to screw with it..
A 6PPC loaded wide-ass-open easily burns all of it's powder in a 21" barrel, and there ain't a lot you can do about it(including screw it up). It's charges are not typically weighed, because they don't have to be, given it's sliver of application..

But a 6PPC is not a long range HUNTING cartridge, and hunting cartridges cannot be run at 6PPC extremes -ever. Well, until a better barrel steal is invented..

I agree that powder weight tolerances needed for hunting cartridges is tied to capacity. This can be seen using QuickLoad, and QuickTarget.
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Old 08-05-2011, 04:12 PM
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Re: Weighing Powder - How precise is good enough?

So Jeff/Broz, how precise do you go on big cases for extreme long range?
Do you use an electronic or beam scale?

Since we're showing dogs, I just got this in an e-mail. Thought it was hilarious.
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  #11  
Old 08-05-2011, 05:10 PM
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Re: Weighing Powder - How precise is good enough?

"..wasn't it Bruce Hogdon that once said that +/- .15 grain is all that matters?"

Don't know about Bruce but that sounds like him. My comment is based on my own observations. Obviously (or it should be) the tolerable variation will depend a lot on the quanity of powder being burned so that changes a bit with case size.

Thing is, ALL powders burn best (that is, most consistantly) within a fairly narrow but easily and clearly identified pressure range. A properly tested and chosen load will have what I call a "window". or tolerance range, within which small variations mean virtually nothing to accuracy - that's why BR shooters rarely bother to weigh charges and sometimes don't even know the weight of their charges. If we take the time to find the full width of that good performing range, typically .3 to .5 gr. for mid-size cartridges, and load in the middle of it small variations won't matter and the frequency of 'unexplained flyers' will diminish. Only when loading on the ragged edge of the window will small variations in the wrong direction cause problems.

IMHO, those who pay big bucks for a Promethus, etc, scale rather than properly developing a good load that's insensitive to tiny variations are wasting big bucks for no good purpose.
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Old 08-05-2011, 06:35 PM
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Re: Weighing Powder - How precise is good enough?

Well given that this is a 'long range hunting' site there is still ES to be considered HERE.
There are tolerant cartridge/load combinations(OCW), but often they are less than suitable over a range of distances. They can produce tiny little short range groups, and suck to hell for distant accuracy, unless also benefiting with low ES.
Afterall, barrel timing and velocity are two different things that don't hold a linear relationship.

You can hit on barrel timing that provides exceptional velocity tolerance -at one distance. An upswung muzzle at a lower velocity, etc.
But this would prove to be a wreck at some other distances, and it would also require a tight charge tolerance and shooting condition(or tuner) to hold.
Many competitors have seen that load development for this timing -at their intended range, is worthwhile.

Now with LR hunting cartridges it is even more difficult to get a velocity tolerant load AND low ES. Our ranges are not set, our muzzles move a lot, and our powders & pressures are relatively slow & low.
So tight tolerances on charge weight(w/resp to capacity) isn't a bad idea.

David Tubb implied benefits to charges taken to the granule with his 6xc, and he promoted use of Prometheus(which does).

Last edited by Mikecr; 08-05-2011 at 06:40 PM.
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Old 08-05-2011, 08:46 PM
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Re: Weighing Powder - How precise is good enough?

Mikecr is correct that we not only need a tolerant load, but also a load with low ES in velocity. If we're only shooting to 700yds maybe 800 yds, then low ES isn't quite as important as it is when shooting to 1000 yds and beyond.

Perhaps Tubb is advocating the labratory scales now, but he wasn't when he produced the dvd on reloading for highpower that I've seen. He used a powder meter and standard scales, and was getting single digit SD's with those tools (according to the video anyway).

I am not trying to say that it's a waste of money to get a labratory scale........don't know for sure, never owned one........but I believe lots and lots of people have gotten great results without one. Fact is, I know a guy that is a 1000 yd Club member of the VHA, and he did it on a prarie dog. He doesn't even trickle his charges......simply uses a meter and calls it good.....I specifically asked him that question when we were talking about Varget vs H380. I told him that I'd rather use H-380 because it meters like hot butter and that I have to trickle Varget onto the scale (which takes alot longer)............He said that he doesn't trickle it even with Varget. He just sets the meter to throw an average charge of X grains and calls that good.

Specifically speaking of the RCBS chargemaster scale........how accurate are they compared to a "normal" balance beam scale..?? In my limited experience, not very accurate. I can put the same case on my Chargemaster scale 5 different times and get 5 different readings, within a few tenths every time but not the same. Both my balance beam scales will repeat exactly with that same case, every time I weigh it...........Yet, some claim to get excellent LR performance with the Chargemaster Dispenser.?
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Last edited by SBruce; 08-05-2011 at 09:14 PM.
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  #14  
Old 08-05-2011, 09:13 PM
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Re: Weighing Powder - How precise is good enough?

"...tight tolerances on charge weight(w/resp to capacity) isn't a bad idea."


A bad idea? No, it's not bad, as such. Extreme spread IS important for long range shooting but there's MUCH more involved in obtaining low ES than precise duplication of charges. I don't think that even counting the individual kernels of powder for truly exact charges will make the difference in ES that several other factors in developing a load will exceed.

Part of the obsession with scale and powder precision is just because it seems so logical but getting more precise than maybe .1 gr. is largely pointless - maybe entirely so - because small internal variations in individual case volume, differences in individual primer heat, even changes in the ambient temp on powder burn rate produces more potential velocity variation than truly tiny powder charge differences. IMHO.
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