Powder weight loss?

[LE-28]

I have the Hornady bench scale which is probably the same load cell used in the Hornady auto charge. After reading this post yesterday I tried it on mine.

I turned the bench scale on for 10 minutes, it sat at zero. I put the 10 gram weight in it and it stayed at the correct weight for an hour without moving. I didn't even calibrate it.

I usually turn it on for an hour before I start and I've never been able to catch it lying to me. I have fluorescent lights in my loading room and it doesn't seem to bother mine at all. When the furnace comes on it will start moving around if I don't have the door open in the room. But that from wind currents.

I have a Hornady auto charge on order right now so I will be trying this theory out with it when I get it.

[1stmar]

9:34 placed a charge of 127.1 grains on my auto charge, at 9:41 it weighed 127.0, at 9:53 it weighs 126.9. Honestly I'm not sure what this tells me. I would never leave powder on a scale that long. Again keep in mind my scale is I my garage and it's 32 degrees out today. The scale was warmed up for over 30min and I turned off the fluorescent lights. I'm going to repeat this with my balance beam. I don't consider this an issue. At 10:02 it still reads 126.9.

[Bart B.]

Note that those strain gauge elements in digital scales are not exactly 100% repeatable for a given weight compressing them. Nor is the voltage across them exactly the same all the time. So a given weight will not have exactly the same reading across several cycles of weighing it. They all have tolerances. The better scales have a lower tolerance range spec'd so be happy if you scale meets its specs.

One other variable that's not electrical; the mechanics of the scale's platform to the strain gauge. It doesn't have exactly the same friction from weighing cycles.

Measuring stuff has tolerances. We pay more for stuff with less tolerances in its operation. And put up with those tolerances in stuff we pay less for.

Unless one shoots their bullets into sub 1/10th MOA all the time, anything smaller than a 1/10th grain weight difference for powder charges is a waste of time.

Comparing a given weight's numbers between a balance beam and digitial scale may well show a 1/10th grain difference; maybe more. I don't think that's a problem for reloaders. As long as the scale of your choice is repeatable to no more than a 1/10th grain difference, that's enough. Benchresters meter powder charges with a 2/10ths grain spread shooting 1/4 MOA groups at 300 yards.

Exact charge weights' are about 17th down my list of what's important for best accuracy. Too many other things need to be right before charge weights need to be exact, or even with a 1/10th grain spread.

[Valornor]

Only time I leave the powder on the scale long enough to notice it drop weight is if I get interrupted from my normal rythem. It doesn't take long though. It's good to know I am not the only one seeing it.

I usually give myself a tenth of a grain leeway on loads. The scale will dispense one tenth over, but if it's two tenths over it errors out and says over charge. Usually I'll just tap out a miniscual amount of powder to get it close enough before trickling the remainder.

The scale is repeatedable in terms of what it measures so it's worth that to me. I'm not going to be real concerned when it wanders.

[Jerry45]

Mine is in the garage with florescent liteing above the bench. I've never had it give a bad reading while I was steadly loading. Verefied with Dillon electronic and beam scales. Only time it has given falty readings is, as I said, if it sits for a while with a charge in the pan. Even then it only shows a few10ths. of a gr. difference. Lights, wind, who know. All I know is it has been accurate to within 1/10 of a gr. while steadely loading.

[Ozzieman]

I have an older RCBS that did that to me once. I use a set of calibrated weights to insure its working and measuring correctly then one day I noticed the same thing.
I do the same as others by letting it set for several hours before I use it
This one time it was me being stupid. I have a desk lamp that has a 120 watt bulb and I put it a little too close to the scale. I was into the second block of 50 with powder and check every 10th.
Since the scale needed to be zeroized several times and was getting worse I checked one of the first block and it was heavy by 0.4 GR out of a 7 GR load.
The problem was that the light had heated the scale.
Dumped the entire set let it cool down and never had the problem again.

[1stmar]

Deleted

[old roper]

I have RCBS 10-10 beam scale and I also have RCBS 1500 scale I have weight check and use 50gr check zero on beam scale then turn on 1500 scale hit zero and weight powder from beam scale and it may vary 1/10 of grain and if it's on the plus side it will always be on the plus side it won't go back and forth.

I know some of the BR guys are using chargemaster if no elec there using a battery charge pack. Also read about some using small plastic vials with pre weight powders for loading at the range.

[marine6680]

Someone mentioned hysteresis, but didn't get it quite right on what it is.

Mechanical systems are the most susceptible to hysteresis... Which basically is, as the system is moved closer to one end of its limit/scale, as it is returned to neutral, it does not settle down to neutral/zero completely, it will read a little in the direction the mechanism was moved to before.

A good system will eventually resettle to neutral/zero after a bit of time, or if allowed to move slightly in each direction of movement.

Using a scale as an example:

Lets say you zero out your scale, and then you take a set of calibrated 10gr weights and start placing them on the scale one by one, measuring the weight each time as it increases... 10... 20... 30... 40... so on and so on.

Now start taking those weights off one by one and check the indicated weight... 40... 30... 20.05... 10.08... 0.1... That slight error is hysteresis.

Electronic scales and systems have a warm up time that they need to minimize such errors. I use test equipment all the time that needs a warmup period before any readings it produces are considered valid. Small errors can be a big deal for some things... Though anything less that 1/10 of a grain isn't really an issue from what I understand. So long as you are not pushing past max loads anyway.

[rox]

9:34 placed a charge of 127.1 grains on my auto charge, at 9:41 it weighed 127.0, at 9:53 it weighs 126.9

So, it drifted 0.2 grains in 20 minutes. Extrapolate that to an hour – worst case you have 0.6 grains error over the course of a 1 hour loading session. That would be quite significant.

Ok, so you won't leave powder on the scale for that long, but it doesn't only drift when it has powder sat on it, it drifts all the time!

But: if the balance returns to 'near zero' for a short period each cycle it can correct this drift. In the case of automatic dispensers that's fine - dispensers 'see' zero each time you place the empty pan on the balance so they can correct continuously. But if you manually throw and trickle to weight using a strain gauge digital balance, the typical sequence is to throw the initial charge from a powder measure before placing the pan on the balance, then trickle up to final weight. In this case the balance never sees zero, so any drift could go uncorrected and accumulate as long as you are loading.

There's an illustration of this in the instructions for the RCBS Electronic Trickler, which 'tops up' a thrown charge using an IR link to a digital balance. After picking up the pan and emptying the previously dispensed charge, you could throw the next initial charge before placing the pan on the balance – after all, you are already holding the pan. But according to the instructions: “Empty the powder pan and return it to the scale. It is imperative that the scale be allowed to re-zero itself between each load" (bold text as in the manual). Only then can you take the pan back off the balance to throw the initial charge from the powder measure before placing it once again on the pan to allow the trickler to perform the final top-up.

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[rox]

Bart,

Exact charge weights' are about 17th down my list of what's important for best accuracy.

I'd love to know what your 1 to 16 are.

In your description of the Palma ammo (1992?), wasn't it the degradation of powder measure accuracy that was held responsible for the poorer performance of the later ammo batches? i.e. your 17th most important factor was the number one cause of reduced performance!

Benchresters meter powder charges with a 2/10ths grain spread shooting 1/4 MOA groups at 300 yards.

Many shooters seek out 'nodes' which are tolerant of variations in charge weight – it's one of the reasons why benchresters can get away with such apparently variable charges and still get reasonable results. But they do this *in order* to be able to throw charges at the range. Most of us (non-benchresters) don't need to load at the range using a powder measure, and since I can produce very accurate charges I don't need to consider 'nodes' or do ladder tests or OCW - I have the freedom to choose the charge to meet my load requirements. I have no doubt that since I moved away from using a ChargeMaster and started producing charges to less than 0.1 grain tolerance the ammo performance has improved, whether it's 1000 yards Palma, 300M ISSF or F/TR. My philosophy is not to do anything unless I can show that it 'adds value', so there are a lot fewer than 16 items ahead of accurate charges in my list.

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