Is volume is more accurate than weight, a personal observation

[R.W.Dale]

Most bench shooters will tell you that volume is the more accurate means for measuring charges than weight, well today I made an observation that vindicates this for me.

Last night at 3am I loaded 50 .32acp using 2.2grains of WW231 using my uniflow powder measure with a micrometer metering tube. When I set up for this load I looked at my log book and set the measure to 003.5 that I had been using all along for this load. Upon double checking with my Ohaus balance and a cheap digital both scales concluded that I was about 0.2 of a grain light at 2.0g by weight, after some deliberation I decided to believe my notes and uniflow and loaded up 50 rds on the 003.5 setting I had always used. When finished knowing I would load more when I woke up I left everything as it was capped off the lid on the powder measure closed the door and slept til noon.

fast forward to 2:00 PM today loading up another 50 rds with the uniflow still set at 003.5 untouched from earlier both of my scales now say that the charges thrown weigh the desired 2.2grs

SO what happened in that time period when away from my loading gear, either.


A changes in humidity effected both scales <doubtful>

or
.
B the weight for a given volume of ww231 changed for some reason or another

Also be mindful that my reloading operation is inside a climate controlled room

scientific: not hardly but interesting none the less. Anyone else made similar observations or just care to speculate

 

[MCMXI]

krochus, does your hopper on the powder measure have a baffle in it such as this?

http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=830897

RCBS says "The Powder Baffle controls the powder flow and the pressure of the powder column on the metering unit."

Could it be that the volume (and hence the weight) of the dispensed powder is changing based on the amount of powder in the hopper. Intuitively you'd think that the more powder in the hopper the larger the dispensed load but intuition is often wrong and you found exactly the opposite (assuming you didn't fill the hopper today before resuming).

Personally I don't believe for one minute that measuring powder by volume "is more accurate" than measuring by weight, whatever "more accurate" means ... in fact I'll say categorically that it's complete BS!! One is definitely faster than the other, and the fact that many benchrest shooters load by volume and get good results simply confirms my opinion that there is a reasonable margin of error when dispensing powder. Some here (with digital scales) get so hung up on 0.1 and even .01 grains of powder without thinking about numerous other factors that have a MUCH larger deleterious effect.

 

[45crittergitter]

Looks like "B" is the correct answer, meaning that even if the volumetric measure does not change, it's sometimes wrong, because when the density of the powder changed, so did the charge that you loaded. Throwing the same volume, but a different mass, does not result in accurate charges by weight, which is how all smokeless charges are given throughout the industry. Ever wonder why charges are listed by weight and not volume....?

 

[R.W.Dale]

Throwing the same volume, but a different mass, does not result in accurate charges by weight, which is how all smokeless charges are given throughout the industry.

not really: I'll bet dollars to doughnuts there isn't an ammo manufacturer out there that weighs charges for factory ammo

Throwing the same volume, but a different mass, does not result in accurate charges by weight,

But does it result in more accurate/consistent charges from one batch to the next? When the density changed more propellant wasn't created inside the given volume discussed.

 

[Remo-99]

Could it be that the volume (and hence the weight) of the dispensed powder is changing based on the amount of powder in the hopper. Intuitively you'd think that the more powder in the hopper the larger the dispensed load but intuition is often wrong and you found exactly the opposite (assuming you didn't fill the hopper today before resuming).

I have noticed that even with a baffle on the powder hopper, there can be some powders that will vary slightly, depending upon the powder level in the hopper.(a baffle minimizes this, but often won't eliminate it completely).
Some long extruded powders don't seem to flow as well, under more weight of powder, than they do with less weight, thus ineffiently filling the metering volume.

It may not be just limited to extruded powders either. And some powders (like flake powders) seem to have an opposite effect. These are just some observations that i've noticed.

 

[MCMXI]

care to cite any proof of that opinion

Uh ... common sense!!

Let me get one thing out of the way, dispensing powder with a Uniflow or similar is FINE for reloading because it has the potential to be ACCURATE ENOUGH. But your comment ...

volume is the more accurate means for measuring charges than weight

... just isn't true. Measuring by volume is a valid technique for numerous applications where the "thing" being measured is homogeneous such as water. However, powder isn't homogeneous because mixed in with the powder is AIR and the distribution and volume in the measuring cylinder is the realm of statisticians. When you weigh powder, the air "trapped" in the powder has negligible mass compared to its volume and so has negligible effect on the weight.

Of course commercial ammunition is manufactured by using the volume method because it's FAST (hence cheaper to produce) and as already mentioned ACCURATE ENOUGH!!

 

[MMCSRET]

Unless you weigh each and every charge you are loading by volume and spot checking by weight.

 

[Walkalong]

Unless you weigh each and every charge you are loading by volume and spot checking by weight.

True.

I believe consistent volume is more important than consistent weight, but with most powders, consistent volume does give you consistent weight.

I have NEVER weighed a charge for my Bench gun, never.

 

[Soybomb]

I'll bet dollars to doughnuts there isn't an ammo manufacturer out there that weighs charges for factory ammo

I bet you might be right! I also bet that part of the reason most of us reload is because we find our loads more accurate. Factory procedures may be time and cost efficient, but they might not produce ideal results. I also bet that factory's powder storage facilities keep their powder at a pretty constant temperature and humidity, something that probably fluctuates more in our homes.

 

[R.W.Dale]

I don't know, factory ammo is pretty darn good nowadays, I doubt my handloads could best federal's gold match line in the calibers they offer it for

OH shure my 7.62x39 loads are light years ahead of any factory offering, but I doubt my 168grn 308 loads are any better than the federal stuff

 

[MCMXI]

I believe consistent volume is more important than consistent weight ... I have NEVER weighed a charge for my Bench gun, never.

... so how would you know?

I doubt my handloads could best federal's gold match line in the calibers they offer it for

Don't forget that the components used in commercial ammunition are relatively easy to optimize. Case weight, bullet weight, case length, primer pocket, flash hole, crimp, etc. All of these variables have a significant effect on the final product but they can be controlled in a mass production process. As I've said before, the powder charge can be controlled too within some optimum range but I won't presume to know what that is. Suffice it to say that measuring powder by volume is fine but it's not as accurate as measuring it by weight ... BUT, who cares, because a well made volumetric powder dispenser works just fine for many, many people and for commercially made ammuntion.

 

[R.W.Dale]

Suffice it to say that measuring powder by volume is fine but it's not as accurate as measuring it by weight ...

perhaps some form of testing is in order....

 

[RecoilRob]

My personal observation loading H335 is that once the powder measure is set, it will throw charges to the tenth or less. No need to weigh them at all.

But....if you change cans/lots of powder, odds are the measure will need to be adjusted to throw the desired weight.

The volume didn't change, but the weight did. And, I've found that 26grns shoots pretty much the same regardless of the volume it took to throw it. If you don't adjust the measure or weigh the charges when changing lots, you can be a couple grains high or low....which probably will affect the POI.

 

[MCMXI]

perhaps some form of testing is in order....

Hmmm ... I have a Redding 10X-Pistol and Small Rifle powder measure, an RCBS ChargeMaster 1500 and access to a Mettler XP504 analytical balance accurate to 0.1 mg (0.0015 grains). I suppose to be thorough I could use different powders. Currently I have Reloder 15, Reloder 22, WW231 and Trail Boss. I could measure out 2.5, 5.0, 10.0, 20.0, 40.0 and 80.0 grain loads using the digital scale followed by the Redding 10X, weighing each one with the Mettler balance. 10 loads of each powder at each weight for both measuring systems would mean 480 loads!!

I just realized, the Redding 10X will only measure up to 25 grains so that reduces the work to 320 loads!! Also, Reloder 15 and Reloder 22 are sufficiently similar in shape/size that I could eliminate one of them so now that means I'd only need to measure 240 loads.

 

[762 shooter]

I think that the size of the powder grains would be a big factor in consistency.

I can reduce the volume of a given weight of say FFg black powder by drop tube or vibration, due to the air spaces between the grains.

I have noticed that the first few throws of a powder measure after sitting on a reloading bench that I was working on are heavier due to settling.

Volumetric measurements can be very consistent but your procedure must be very consistent also. I doubt cartridge manufacturers accept the first few hundred rounds of a run until they are satisfied they are all the same.

 

[edSky]

Newbie Powder baffle question

The baffle goes in the bottom of the hopper. So ... I'm guessing it works by lightening what passes by it. When the column of powder is greatest, the baffle acts to simulate a lighter (powder column) mass. Is this right?

Thanks for letting me talk myself through this. At first when I saw my baffle I was ... baffled by it.

 

[Edubya]

I use a Dillon 550. When I change caliber, start a new keg, or alter the powder charge, the first thing that I do (after adjusting the volumetric measuring device) is throw ten loads to weigh on my 10-10 scale. This will come out to a +/_ of .5 gr. of my desired amount or I'll start over until it does. After that I'll check a single charge after about 100 loads. I believe that volumetric works very well, but there are many variables and I do not trust electronic scales.
Just another perspective.

 

[rfwobbly]

"The baffle goes in the bottom of the hopper. So ... I'm guessing it works by lightening what passes by it. When the column of powder is greatest, the baffle acts to simulate a lighter (powder column) mass. Is this right?"

IMHO it works by supporting the excess weight of the column of powder above the baffle. It keeps this weight from compressing the powder about to enter the chute.

If the full weight of the column were to press on the chute, the volume in the chute would slowly decrease as the weight (height of the column of powder) decreased.

So when you insert a baffle, the effective column height that is pressing on the chute is only that from the chute to the baffle. That short distance is far more constant than the total height of all the powder.

If you have ever seen a hummingbird feeder, where a raised reservoir is only allowed to replace the liquid taken from the pool below, then you can see the parallels. The two are very similar.

 

[Remo-99]

So ... I'm guessing it works by lightening what passes by it. When the column of powder is greatest, the baffle acts to simulate a lighter (powder column) mass.

edSky,
Your thinking is correct, this especially noticed with flake powders, where they are easily influenced by the slight pressure difference of a full powder hopper as opposed to a near empty hopper.

The pressure can compress the volumetric measure of flake powders, enough to effect accuarcy and even put powder weights over a maximum level, if weights were checked before refilling the powder hopper.

That said, I've also noticed the opposite effect with some powders(often long extruded rifle powders) by using a baffle in the powder hopper. Where as these powders relied upon a certain level of pressure above, to help them flow better and meter a consistant charge.

 

[Steve C]

This is kind of a silly argument.

The mass (weight) of the powder determines the volume of gas that will be generated in the cartridge as it burns and the rate at which it is generated determines the resulting pressure. The volume of the powder is important only in how it relates to the mass of the powder.

If the powder was a liquid there would be a direct correlation between the volume measure and the mass of the powder. As a particulate solid there still a direct correlation between mass and volume but the practical methods of obtaining a volume of powder produces inconsistencies.

Typically we use a volume measure to dispense powder because its quicker. We set that volume measure to throw a charge determined by weight of the powder according to the loading manuals. By their nature a volume measure isn't 100% consistent due to the way its operated, the settling of the powder as the movement of the measure vibrates the powder in the hopper, and other factors. Generally in the overall scheme of thing the inaccuracies of weight between charges dispensed by volume within a short time period are small enough to be insignificant.

It is still important to check the weight of the powder charges being thrown, usually every 10th throw to see if they are maintaining acceptable variatation in weight.

 

[cracked butt]

Check the two loads through a chronograph, everything else is just speculation.

 

[gun4funtime]

How hard you throw the handle on you powder measure will change the weight of the charge being thrown. If you are running a vibratory case cleaner on the bench, it will change the weight of the charge being metered from your powder drop.

You want everything to be as constant as possible, that would be the weight of a charge. If they very, then look at what you are doing different each time. Even the amount of powder in the hopper will very the weight at times. The volume would be different also, a loose volume-- to a compressed volume. so I really watch the weight of the charges.

 

[kelbro]

Not real scientific but I have observed something a couple of times that says volume is pretty important. I had some 223 cases that had a couple of grains difference in water volume capacity. The interesting part is that they both shot to the same POI and the same velocity through the chrono when they were both filled to the bottom of the neck. Measured weight of the powder between the two was roughly 1.5 gr. different.

 

[Gewehr98]

One way to find out...

Somebody buy me a Prometheus powder scale, and I promise I'll do all the weight vs. volume testing for free!

http://www.6mmbr.com/prometheus.html

 

[Remo-99]

I had some 223 cases that had a couple of grains difference in water volume capacity. The interesting part is that they both shot to the same POI and the same velocity through the chrono when they were both filled to the bottom of the neck.

Kelbro, has touched on a valid point, where volume is 'more' critical than weight.

But fankley, if headstamps are the same where case volumes are close, unless the rounds are used for Benchrest precision shooting, I can't see a 'real' advantage of one way over the other.

I weigh charges when working up loads, then adjust a powder measure to throw that weight of charge and check periodically for the thrown weight.

If done consistanly it varies only very small fractions of a grain.
Which gives me ammo capable of better accuracy, than I can shoot it, out in the field with all the other variables, like my skills are taken into account.