Volume vs. weight of metallic cartridge propellants

[SRMohawk]

Gentlemen,
Last night I was at Sinclair International's website shopping and decided to peruse their bulletin board to see if anyone had posted any reviews on a few of their newer product offerings. And at length, I stumbled onto something that REALLY blew my hair back. In response to a novice handloader's inquiry about digital vs. balance beam scales, a guy identifying himself only as 'Les' recommended to this man that he invest in a state-of-the-art powder thrower/dispenser -- specifically, in one of the Harrell products -- and not to even bother weighing charges. The rationale for this is what was truly intriguing.

He explained that by virtue of the way they are manufactured and/or the way they work, that metallic cartridge propellants MUST be dispensed by volume rather than weight in order to reproduce a given MV with a great degree of consistency. I immediately took this information to my wife (who has a Ph.D. in physical chemistry from Rice University) and asked her about it. She then -- having never really watched me assemble cartridges -- asked to see some of the propellants I use in manufacturing ammunition. And upon examination of a couple of different samples of the stuff, replied by telling me; "That guy is absolutely right! This stuff can't possibly be the same density or mass from granule to granule! And that means that any given number of charges weighing X number of grains won't actually equate to the same amount of kinetic energy from charge to charge."

:banghead: But how in the hell are any of us getting extreme MV spreads across 10, 20, or even 30 rounds of less than 50 fps by weighing the propellant!?!? I want feedback here, boys! And I mean lots of it!!!

 

[armoredman]

I had heard the top shooters don't weigh thier charges, but load by volume. Having said that, I weigh every tenth charge thrown, and I get fairly even results.

 

[stoky]

This debate has been going on for quite some time. One way that it might be resolved is to load up (oh, let's say 100 or ask your wife what number would be statistically significant) one batch of rounds by volume and another batch by weight. Please report back with standard deviations in velocity and group sizes.

thanks

 

[Jim Watson]

I am not a physical chemist but I recall enough to say that ideally propellants are defined groups of chemical compounds whose energy is rated in things like calories per gram. And all load data is specified by weight, in grains avoirdupois here in the Colonies.

However, in loading ammunition, volumetric measurement is the only thing fast enough for commercial production and is convenient for the individual handloader, so the energy per unit volume is important and needs to be kept consistent.

I have read that powder companies have established their manufacturing processes and blending procedures so that variations in properties tend to be offsetting. That a dense lot of powder will be a little less energetic per gram than a bulky lot so that the energy per CC will be very nearly the same for volumetric handling. Also, powder is not soluble or reactive in water but it can adsorb or desorb moisture depending on shop humidity. So a given volume can weigh more or less, but you are getting the same amount of nitrocellulose and the same energy.

A benchrest shooter, using a precise volumetric measure, finely granulated propellant, and good technique CAN produce more uniform loads than if he had weighed them. Many of them load at the range where it would be difficult to operate a scale anyhow.

On the other side, if you are loading coarse powders with an ordinary measure that crunches its way through a charge, vibrating as it shears the long granules, you might generate enough inconsistency to affect the uniformity of velocity and accuracy on target.

Me?
I load Ball-process powder by volume. It meters consistently enough that the volume versus weight debate does not even come under consideration.
But the crunch-grind of extruded powder and the resulting charge weight variations make me nervous, so I weigh them, at least for target ammo.

Might be worth some test firing, eh?

 

[SRMohawk]

Jim,
I've been using a piece-of-crap powder thrower (I think, at least) since I got into precision rifle and/or manufacturing my own ammunition some years ago. It's an RCBS Uniflo measure. And it dispenses powder charges just as you so vividly illustrated -- by grinding, shearing, and/or crunching them off a vertical column of powder from below! And I haven't done anything about this because I've put so much faith into the weight of the charges, using both quality balance beam and digital scales. I currently weigh all charges on a Dillon D-Terminator digital job and then check them with a Redding #2 magnetic dampening balance. But I decided a few weeks ago to give away the RCBS Uniflo measure, replacing it with the big Harrell Premium Culver measure. I also plan on picking up one of the Acculab digital scales Sinclair starting carrying late last year. Then we're gonna see what the score is here, just as Stoky admonished me to do so.

I just had my 6.5x284 Norma re-barreled and it's broken in and shooting well. But I haven't engaged in any of the serious 'post-graduate handloading' (how the boys at Sinclair International refer to it) with this barrel yet. I always see what a barrel will shoot with half-ass stuff, first. Then, if it'll cut sub-0.5 MOA groups for 5 shots, I start weighing cases, turning necks, and polishing the inside of the case necks.

Give me 2-3 weeks and I'll be back to share the results!

Regards,
SRM

 

[444]

High School Grad here.

Lower third of my class at that.

Please explain this to me in very basic, practical terms.
If you don't base your charge on weight, how do you initally set the powder measure for the first charge ?
How do you get around the fact that load data in manuals is given in units of weight ?

FWIW, I own a Harrel powder measure.

 

[RON in PA]

444: You're correct. The right way to set up a powder measure is adjust it (change volume) so that it throws a mean weight (I use the average of ten throws) equal to the charge you want.

 

[esheato]

I wish I had the answer to this as I've been searching for it for a few years now.

I started with a PACT digital dispenser. Way too slow.

Next was an RCBS Uniflow and I didn't like it compared to the digital options. At this point, its sole duty is light plinking loads using Unique.

Recently moved up to an RCBS 1500 Chargemaster Combo. Much faster, but I find myself calibrating often due to obvious differences in how full the cases appear (even after tapping them to settle the propellant). I often feel like I'm chasing my tail. The numbers over the chronograph tell the same story also. SD, ES and MAD vary quite a bit (ES is typically over 100 fps).

Growing tired of the chase, I decided to try a high-end volumetric measure...I purchased the Harrells Premium Culver measure. I ran some IMR 4064 through it and it was quite crunchy resulting in some erratic throws. I switched to H322 and it was better. The throw was much more smooth and the loads were more consistent. I'm fairly certain the measure will throw ball very well.

I have yet to shoot anything loaded with the Harrell. I'm waiting on a powder shipment from Powder Valley. In the mean time I'm practicing my operation of the measure.

Looking forward to the results SRMohawk.

Ed

 

[SRMohawk]

Whoops! Sorry 'bout that 444! Thanks for takin' care of that for me, Ron!

 

[Jim Watson]

Well, I'm not a benchrest shooter but I recall reading, back when Dave Wolfe and Neal Knox put some technical stuff into Handloader and Rifle, that it was common for benchresters to exchange load data in "Culver Clicks" instead of grains. Pure volumetric throughout.

But the factories publish data by weight and you have to have someplace to start for the usual stuff.

I am not surprised that even a Harrell was "crunchy" with 4064. There is only so much that precision manufacture can do for the basic design of a rotary cavity and I think that a large part of their reputation is built on use of fine grain powder. There have also been reports that accuracy is not as dependent on exact powder charge as you might think.

When I started loading for F-class, I got the beam balance back out. I can watch it sneak up on the reading as I trickle powder in. The digital would jump, jump, jump and was easier to overshoot if I twirled the knob a little too hard. I guess the electronic dispenser is The Answer but I'd rather put my money into a new barrel for my Savage.

 

[Grumulkin]

I weigh my charges since I think my scale is significantly more accurate than my powder measure and it works for me especially with powders like IMR 4064 that don't measure consistently.

Besides, how is one to make fine adjustments in a load if not with a scale? Is there a measure out there which will let one make small cubic centimeter adjustments? I don't think so. If one was to use volume with a stick powder, the mass of powder would vary somewhat depending how tightly it was packed anyway.

It sounds to me like all the hoopla about volume being more important than weight has its origins in someone wanting to sell a particular piece of equipment. I would need a lot more evidence before I would bite.

It is true that with some cartridge/gun combinations, powder weight doesn't make that much difference. I've been particularly impressed with a 22-250 I've been loading for recently. In working up loads for 70 grain Speer semi-spitzers with IMR 4064, with from 30 to 33 grains of powder, it groups a little less than 1 MOA and with each load and the bullets have essentially the same point of impact even with a cold barrel. I really could load for this one by throwing charges from the measure and not notice any difference on paper; I'm just too compulsive to load this way.

My experience with most cartridges I load for (medium to high volume cases) is that half a grain to a full grain difference in powder weight frequently makes a significant difference in accuracy and in where the bullets hit on paper.

As noted by one poster, the real solution (to a problem I don't really think exists) is to use a ball or short stick powder that measures accurately. I actually try to do this when possible but sometimes it turns out that a stick powder just works better.

 

[USSR]

When I started loading for F-class, I got the beam balance back out. I can watch it sneak up on the reading as I trickle powder in. The digital would jump, jump, jump and was easier to overshoot if I twirled the knob a little too hard.

I'm with you, Jim. I shoot F Class as well, and trickling up on a balance beam works for me as well.

Don

 

[30Cal]

I did some load development about 2 years ago where I wanted to find the best load for 300yds and less using unsorted brass and fairly variable powder weights. I weighed a bunch of cases and set up my strings so that 1/3 of the cases for a given group were well below the average weight (by 1gr or more) and 1/3 were well above the average weight (again, by 1gr or more). In the light cases, I put a lighter than nominal powder charges (by 0.4grs) and in the heavy cases, I put heavier than nominal powder charges (by 0.4grs). I did the same with bullets although there's not a lot of variation to work with in a box of SMK's. So, in each group, I had an even split where 1/3 would give me the worst case low pressure/low velocity, worst case high pressure/high velocity and then nominal.

Just to cut to the chase, I didn't see any difference in performance out of a match rifle at 200yds between those batches of worst case oddballs and the ones that I'd built up with carefully weighed and culled components. I now only weigh charges occasionally to verify I'm not going to blow myself up.

 

[USSR]

High ES and SD readings as a result of thrown powder variations are not likely to show a pronounced effect on targets at short range (100-300 yards), but will definately result in a large vertical dispersion at 1,000 yards.

Don