Powder measure tolerance range

T

Tony Z

New member
Never having paid much heed to tolerance range of my 3-1/2 decade old Lyman powder measure UNTIL yesterday. Always seems to have been repeatable against my old Lyman scale, but alas that scale seemed to have disappeared. The replacement is the RCBS 5-0-5, which seems OK, but made cheaper than my old Lyman (RCBS bought 4 or 5 or 6 years ago).

Anyhow, yesterday, I started loading up some .45 Colts for my Henry lever action. The Lyman measure was already set-up for 4.7 grains of Unique and as I loading 200 grain copper jacketed RN bullets, I found that 9.4 grains of Unique is a middle of the road starting load for plinking, and should be very easy by just double throwing the powder measure.

Last year, I bought a Frankford Arsenal digital scale for double checking the RCBS, and when I began throwing powder for the .45 Colt, it looked like I was getting a +.1 and -.1 grain variation from the RCBS. After double and triple checking both scales, the variation remained. At this point, I got out my decades old Ohaus balance beam lab scale (don't ask) to check the other scales and the scales are weighing pretty dayam close. Now it is time to give the powder measure a look-see and it appears the +.1/-.1 grain variation is coming from the measure. Checking all screws, etc. and everything is tight. I decide to do a single throw and adjust to 9.4 grains of Unique and the same variation is there, and hence my question: Has anyone noticed a variation of +.1/-.1 grain variation in their Lyman powder measures (using a powder like Unique)? Anyone want to offer suggestions? I'm leaving for the day, but late this evening, when I return, I think it is time to fully disassemble the Lyman to see what may be awry. But I'm still left wondering what is an acceptable tolerance range for a powder measure.
 
Yes. That coarse Unique flake is notoriously hard to meter accurately because the flakes flatten out into interlocking arrangements that can bridge the metering cavity, resisting filling it well. That bridging is bad enough the Lee recommends against metering Unique in their Perfect measure at all. So your Lyman measure is doing an exceptional job of handling it. I've watch my Dillon measure throw Unique off by 0.3 grains. The general strategy is to measure the variation and make sure the worst case high charge doesn't exceed the maximum load you find acceptable.

In revolver and pistol cartridges, that variation isn't really an issue anyway. For one thing, 4 moa is considered adequate match accuracy with those weapons. For another, if you experiment with them at the range, you find that for most handgun ranges, the faster rise of the muzzle and shorter time it takes the bullet to leave the muzzle tend to compensate out point of impact as charge weight increases. You find the weight of the bullet has a lot more effect on point of impact than exact charge weight does with these weapons.

Shooting pistol cartridges in a rifle can be a different animal because of barrel whip. Most revolver and pistol barrels are too rigid to deflect and whip much in recoil, but rifle barrels sure will. Nonetheless, you'll find you can run those big slow bullets in an Audette ladder even at just 100 yards and by working the load up slowly, identify a flat spot where the phase of the whip tolerates a short span of charge weights. That's a good place to load for accuracy as it exhibits some immunity to precise charge weight.
 
I found a better way to get an accurate average is once you get the weight close. Dump 10 charges into the pan and measure that. Divide by 10 and you have a fast quick average. Keeps you from measuring singles.
I normally do this 2 or 3 times when setting up the powder measure for a new load.
It will also give you how accurate your dumping between the 3 sets of 10.
I find most scales including digital are accurate to +/- 0.1.
Running multiple 10 samples will get you accuracy to 0.01
10 @ 94.2 = 9.42
10 @ 94.3 = 9.43
10 @ 94.5 = 9.45
Average= 9.435
Also if you end up with an average that is high/low > 0.1 between the 3 then you might need to dissemble the measurer and clean.
 
I was just thinking about what Ozzieman suggested yesterday as I was measuring 10 shots across the chronograph! Why wouldn't ES and SD be applicable to powder drops also? I have noticed my Dillon drop being +/- 0.2 grains on BE-86 and Longshot and I thought about averaging it out versus measuring every 10th drop and getting frustrated!
 
I averaged drops since I started, nearly 40 years ago and stayed away from weighing each drop. The reason I did it this time, was that the Lyman was set up to drop 4.7 grains and I was targeting the mid-8 grain range for my .45 Colt Henry rifle. So, I figured I would double drop and decided to weight the charges and that was when I got concerned.

I'm still left thinking that +.1/-.1 is a pretty big range and that +.2/-.2 may be way too big, particularly if you consider the tolerance range of scales used. Maybe John Lee is really on to things by measuring volume instead of weight?
 
When I started reloading 10 years ago, my mentor told me to keep a couple of auto body washers on top of my powder. This was to give constant pressure on the powder being dropped.

I find that even using this method as the powder is being used up and the level of powder decrease in the measure there is small variances when the powder is about half way down. So at that point I add additional powder to the measure and that problem is solved.

Unless it is the last of that powder I always add more powder after loading about 50 to 100 rounds. It should help keep things on target.

Good luck and stay safe.
Jim
 
I can remember a few years back (OK-maybe more than a few years back) someone offering a baffle that looked like an inverted V, to be placed in the powder hopper, to help with fill consistency.

Question: does anyone know if the composition of powder includes anything on the surface to help with "packing/flow" characteristics?
 
Most setups can't even measure closer than .1 plus or minus.

Trying to do better than that when there is no gain is an exercise in futility in my opinion.

You are doing really well there.

You have very good consistency, you have well above average cross check tool set and the difference you see not only can't be done any better, you can't tell the difference.
 
Cwall64,

SD, ES apply to powder measure drops, though the distribution is usually not quite normal, so they can't be handled quit the same way. That is, rather than a bell curve, because the cavity size sets a hard limit to the upper amount of powder you can charge the metering cavity with, the upper direction beyond the middle of the bell curve does not have a symmetrical infinite tail. Same with cast bullet weights because the cavity size puts an upper limit on how much alloy you can fit in.

These single-tailed non-normal distributions are commonly dealt with in statistics, though, if you want to look up how to handle them. One trick is that even though standard deviations don't work quite the same in them, the standard deviation of the standard deviations of samples (standard error) typically does have a normal bell curve distribution. It's just very narrow. So you can work backward from that, if you are so inclined.
 
I dug out a RCBS 505 and RCBS Pro digital. I did not bother with the test weights. I started loading 150 30/06 with 155 grain bullets, mostly LC brass and 4895 IMR powder. When finished I weighed 50 of the loaded rounds. They weighed 405 grains +/- 3 grains.

I used an RCBS Uniflow powder measure. Just in case I dug out a powder trickler. I used Sierra game king bullets, I weighed three of them, the bullets fell into the category of +/-.

F. Guffey
 
Trying to do better than that when there is no gain is an exercise in futility in my opinion.
Click to expand...
Trying to get accuracy to less than 0.1 is not the point. Doing averaging will give you the deviation in accuracy. If your seeing consistent drop averages then your good but if you start seeing more than .1 or .2 out of 10 drops then you need to check your system.
This is nothing more than a calibration tool for your powder measure and the powder your using, not splitting flakes in half.
 
Not only is it really, REALLY splitting hairs to dwell upon a single tenth of a grain, this idea of dropping 10 charges is also not the answer.

If you repeatedly work that lever for 10 charges in a direct, repeated method... you are already deviating from the physical motion of dropping consecutive charges in to brass. And ANY deviation from the process that actually fills your brass may end up showing itself in your weighing of test charges.

You can also see tenth-grain swings or half of that simply by hanging your powder pan differently in the scale or as mentioned, by not keeping the powder hopper full.

We all find our own way and we each need to be comfortable and confident in our process, so if my suggestion to IGNORE a tenth grain variance isn't acceptable, I understand--

and would then suggest that you PURPOSELY build a bunch of loads that you knowingly vary across a whole three tenths and see if you can find even the slightest hint of a difference in any of them.

.32 ACP case with max charge of Titegroup? Perhaps yes. Big fat .45 Colt with a dump of chunky Unique? I don't see it.

Next test:
pull down some factory ammo and chart the variance there. That might also boost your confidence in what we do. Because most of us put FAR more care in to what we are doing.
 
Coming from a statistics background (albeit more than forty years since college), I tend to look at the whole picture, including "stack-ups" of tolerance ranges of all equipment that enter the mix. A +.1/-.1 range at the measure (some here say +.2/-.2 is typical) added to the same tolerance range at the scale becomes significant (especially when you bring in old eyes squinting at a manual scale!). Funny thing, I would have ignored this had I not bought the digital scale and started cross-checking!

I'll repeat what I posted earlier in this thread and that is, maybe we would be better off loading to a specific volume instead of to weight? May have to dig out my Lee dippers this afternoon!
 
Next test:
pull down some factory ammo and chart the variance there. That might also boost your confidence in what we do. Because most of us put FAR more care in to what we are doing.
__________________
Click to expand...

I have pulled down 1,000s of rounds of loaded ammo, AP and tracer 30/06, 8mm57 Mauser rounds of corrosive primers and cases that show evidence of case cutting when fired.

When weighing the powder charge I have been impressed, newer ammo, I have pulled down R-P 30/06 ammo. I was even more impressed when weighing the components, and there is no shortage of tools when it comes to measuring a case. Same thing with the dimensions of the case and weight. The last 5 rounds I pulled down I could not find more than .1 tenth grain difference between the case, powder and bullet.

AGAIN, 5 of 20 rounds did not fire, the 5 that did not fire had at least 5 opportunities with 3 different rifles. The primers were removed, examined and reinstalled back into the same cases. I chambered the 5 cases one at a time into one of my M1917s with killer firing pins, every primer busted off. The conversation started with "What is wrong with R-P ammo?" I suggested they call R-P.

F. Guffey
 
Agree the newer ammo is charged much more tightly than it once was. Machines are better. I once pulled down 20 roudns Winchester Supreme .308 Match loads and checked charges on a lab scale that had 0.001 gram (0.0154 grains) resolution, and found the 748 in them to be within 0.05 grains extreme spread.


TonyZ,

As a practical matter, I reject any load I work up that won't let me throw ±0.3 grains without changing POI as too sensitive to specific conditions.

Using QuickLOAD's temperature tweak for non-compensated powders, I find loading to 0.01 grain error has about the same effect as a 3° change in ambient temperature. Temperature generally changes that much or more during a range session, and it certainly changes more than that between range sessions.

Volume dispensing is found by some to be more accurate than weighing, particularly with stick powders. It has to do with how packing density changes burn rate. When I work up loads for special testing where I want variables as close to zero as possible, I drag out the lab scale, then tare each primed cartridge case and then dispense powder into it volumetrically, and use the the resulting scale weight, seating bullets only those cases that come out within 0.1 grains (±0.05 grains) of being the same. It is utterly unnecessary for most practical purposes, but is good scientific procedure as it gives me powder dispensed by weight and volume simultaneously to eliminate both as variables. The nuisance then is handling every one of the cartridges identically until they are fired, as transport vibration and fiddling and other factors do change the powder bulk density if the load is not compressed. A slightly compressed load has the advantage of locking the powder into position pretty well, to provide some handling immunity.
 
Thanks UncleNick.

Me thinks I'm over thinking things a bit, but in a sense, this discussion has been helpful in learning what the tolerance range of equipment is and the need to keep that in mind when approaching maximum loads.
 
One way I've found to improve metering discrepancies when using Unique is to swap out the pistol barrel on your dispenser with the rifle one.
The larger orifice of the rifle barrel allows Unique to flow more freely.
This will improve repeatability by about 50%. I use to trickle charge until I discovered this by accident. My dispenser is an old RCBS model, back in the day they provided two barrels, don't think they still do.
 
You must log in or register to reply here.
Back
Top