Weight vs. Volume — The Great Debate
Most competitive long-range shooters weigh powder charges for their handloads. Some even use ultra-precise magnetic force restoration scales to load to single-kernel tolerances. But is weight-based measuring always the best way to fill a case with powder? Another option is volumetric charging. This method fills a precisely-sized cavity with powder and then dumps the charge into the case. A Harrell’s rotary powder measure works this way, as does the sliding powder filler on a Dillon progressive press.
For long-range applications, most people believe that precise weighing of powder charges is the best way to achieve optimal accuracy and low ES/SD. However, those short-range Benchrest guys do pretty darn well with their thrown charges, at least at 100 and 200 yards.
Our friend Dennis Santiago recently observed something that made him scratch his head and wonder about weighing charges. His AR-15 match rifle shot better with volumetric (cavity-measured) charges than with weighed charges dispensed by an RCBS ChargeMaster. Here’s what he reports:
Cavity vs. Dribble (Dennis Santiago Report)
I had the chance to compare nominally identical ammunition loaded two ways. These were all .223 Remington match loads using 77gr Sierra Match Kings over 23.4 grains of Hodgdon Varget. Same gun. However I loaded some ammo with charges dispensed with a Lee cavity-style powder measure while other rounds were loaded with powder weighed/dispensed by an RCBS Chargemaster. The cavity-drop ammo (with powder dropped from the Lee unit) was consistently better than the weighed-charge ammo. I have no idea why…
So, ladies and gentlemen — what do you think? Why did Mr. Santiago’s volumetrically-charged ammo shoot better than ammo filled with weighed charges? What’s your theory? Gary Eliseo suspects that Dennis’s Chargemaster might have been drifting. What do you think? Post your theories in the comments area below.
Having the unshielded power wire coiled next to the unshielded transformer – another coil – and right next to the unit itself seems like a great way to adversely influence the scales accuracy: dare I say “excessive magnetic flux-uation”…
I have a Chargemaster and I guarantee you that the charges dispensed are NOT consistent. I have a magnetic scale that I use to get accurate charges. The Chargemaster can vary by over a full grain in the charges it throws depending on the powder. I set my Chargemaster to dispense .3 grains less than what I actually want. Then I put the pan on my scale and trickle the last few grains with an Omega dispenser to get charges accurate to .02 grain. My SD and ES are minimized that way. Takes more time but if you need precise charges then the Chargemaster alone won’t do it for you. I did put choke filters on all of the scales – don’t really know if it made any difference but I figure it can’t hurt.
It’s a new known fact the rubs powder dispenser true charge is not what it reads. I’ve tested this and I’ve even tweaked mine as much as I can via software and the straw method and yes it helped but the scales resolution of +/- .1 grain alone is enough to be of concern then there’s the actual weight weighed on a lab grade scale with a resolution of +/- .01 grains that tells the true story of weighed charges from an RCBS.
I have a similar setup and have had the same experience as Mark Cheesbrough mentioned. I added some cord magnets to both ends of my scales and saw some improvements but the RCBS auto dispenser still throws some +/- .7gn charges. Next I’m going to start using the static cling fabric spray to see if it helps.
I think that the Lee auto-disk probably does a better job than the RCBS… But a properly set up ultra precise magnetic scale will out preform both.
I suspect that the real variable to be measured (give two charges of exactly the same weight or volume) would be surface area of all the powder cereals. My guess is that affects the burn rate and how the pressure develops. Thus affecting muzzle velocity.
Loading 30-06 for 300 meter big bore competitions, peep sights, sling and prone position, I have found that volume measurement from the humble RCBS Uniflow powder measure more than equaled carefully hand weighed charges.
I would like to see a scientific test with this, including weighing of volume charges.
Would be interesting I’m sure.
To really understand what has taken place here, it would be desirable to have a really high quality scale and weigh all charges, both from the Chargemaster, and thrown. Beyond this, it would be nice to have some chronograph data. With good technique, it is possible that a reloader could throw that powder more consistently than a Chargemaster would weigh it.
What I found in 20 odd years of shooting is that SD and ES only help the scores when your past 600 yards or are shooting on ultra small targets (300m Intl). What I load to is a node where minor variations don’t add vertical. Every rifle has these nodes. So I throw charges and use the time practicing.
He needs consistent pouring method which effects powder packing density. The lee dumper is more consistent.
I had a long chat on the topic once with a friend who used to run a well known ammo company. He is also a superb gunsmith and LR shooter. He recommended volume as more consistent over the long run.
Why? Gunpowder is both hygroscopic and has a large surface area. It will change mass a fair bit over time for the same volume depending on the RH and your altitude. So volume, which doesn’t change, is a more consistent indicator of the amount of powder you are using for a given load.
He also pointed out that even with the relatively crude, by chemist standards, scales we use, a tenth or two grains plus or minus is basically nothing on a percentage basis compared to the overall weight of the powder charge. For example, 42 gr of 4895 plus or minus a tenth, something I can consistently throw with my Harrell, is a variation of only 0.47 percent.
If we assume, for the sake of argument that there is a liner relationship between powder mass and resultant velocity (NOT!) that 0.47% results in a 12fps variation in velocity. So lost in the noise.
It is the surface area of the powder that has the greatest effect on consistency. This is achieved better by throwing a volumetric charge, rather than weighing each charge.
A strict uncertainty analysis of an auto charge unit shows that they don’t perform as well as a good beam scale for a population. On top of that, they drift. We’ve all seen this with the cheap strain gauge scales.
I don’t think you can say that charges coming from an auto charge are weighed.
I find that I get the most consistent performance by ensuring:
– that the internal volume of my cases is consistent
– that I use the same *mass* of powder in each case
– that this mass occupies about the same amount of space in each case
In other words, I find that given the same mass performance will vary depending on how it stacks up inside the cartridge.
I use Somchem S365 extruded powder and found 0,5 grain spread with a Harrel measure. This seems a bit much to me, so I continue to use my RCBS chargemaster. I would love to use the measure only as it will save a lot of time.
Without knowing the weight of the throw charges its hard to come to a conclusion. Id imagine the quality of the powder measure and the meter ability of the powder used plays a roll as well.
Another good post. Almost got me rethinking my whole charging process. Then i kicked myself and said. Read the target. The details are fun to play with but experiment and check downrange results. They don’t always reflect everything else.
Zedikers reloading book beats this topic to death if you want to really turn this inside out.
M-
In general, there shouldn’t be a great deal of difference between your results (with respect to Chargemaster vs Harrell’s) when using 24 to 24.5 grains of Varget behind 77 SMKs. My own experience shows that both generate acceptable groups in my bolt guns and space guns – around a half minute. When I found that they both shot well enough to make me happy with a service rifle, I quit experimenting and just started loading.
Having said that, there is a distinct difference between a Harrell’s meter and a Dillon meter with Varget. Since it is relatively coarse-grained, it doesn’t flow in a Dillon meter all that well. Lots of people are happy with the Dillon meter – and lots of them shoot higher scores than I do.
What I haven’t done is run a test of the actual weight of loads thrown on a Chargemaster using a very good scale as a control. I suspect there won’t be a great deal of variability between throws, but then that is why we do testing.
I switched to volumetric about a year ago after having issues with my high end scales drifting. So far I have not seen any adverse affects and probably won’t switch back to weighing anytime soon.
This question has already been asked and answered.
Go to my friend Sergey’s site: http://www.preciseshooter.com for a thorough (scientific) analysis of how accurate the Chargemaster is.
Would humidity and temperature not play a role in weighing your charge?
If you use volumetric means then you should get a consistent volume and when weighing this volume,they should all be very consistent weight for the same day.
The next question is what powder measure will give you consistant dumps?
I could be inclined to go with Richard’s friend opinion, because it looks “scientific”. Somehow I once made a dump test with the same ball powder canister, within the same hour for all the dumped charges. I used an empty revolver case which I filled up from the canister through a funnel until it overflows, then leveled the overflow with a knife and finally weighed. After many samples, the weight ES was very close to the same I get when using a volumetric powder measure. So I don’t think the hygroscopic nature of powder explains everything. What I can add is for handgun cartridges it doesn’t seem to matter much which technic you use, so go with the fastest one. But, for large rifle cases (375 Wby in my case) I often go in the single digit velocity ES with weighted charges.
I forgot to mention : “But, for large rifle cases (375 Wby in my case) I often go in the single digit velocity ES with weighted charges”, not so much with dumped charges especially with extruded powders.