Author Topic: scale accuracy (Read 1274 times)

Rickk · « **on:** August 02, 2007, 04:29:53 PM »

I went to weigh up a few charges this afternoon. My electronic scale was working perfectly yesterday. This afternoon I poured powder into a plastic cup on the scale and it was obvious that something was wrong. I always use a PVC pipe cap to make a course measurement... it always comes out within a few percent with 1F powder, and then I tweak it to get the correct reading on the scale.

I poured in a measure full and it was reading about half what it should have been. I repeated this and it came out way wrong every time. The readings also tended to drift around a bit... something it usually does not do.

I changed the batteries... same thing.

The humidity is high... maybe dampness got in there. I sat it on top of the TV set, which tends to be a bit warm, to see if it can dry it out.

I guess to moral of the story is to not rely 100% on a scale, especially an electronic one. Calibrate a volumetric measure using a reliable balance powder scale, and use the measure to make at least course measurements. If something does not seem right, it probably isn't.

lance · « **Reply #1 on:** August 02, 2007, 04:40:24 PM »

well you know how swift i am with computers, so i don't even own an electric scale. i use the tools the old timers used back over a hundred years ago to measure powder charges. and darn it! no two charges are exactly the same either, what's a person to do?

lance · « **Reply #2 on:** August 02, 2007, 05:30:56 PM »

any secret tip would be appreciated, i even try and use the same lots or runs of powder. but that only works till it runs out, then it's start all over again.

GGaskill · « **Reply #3 on:** August 02, 2007, 07:14:35 PM »

While humidity may be a problem, static electricity may be one also. I would say lose the PVC cap and use the metal pan that comes with the scale. If it's not big enough, find a tin can and use that.

Rickk · « **Reply #4 on:** August 03, 2007, 12:53:43 AM »

I found the problem... a grain of powder got under the platform of the electronic scale. I shook it out and it works 100% again. When I put it away, it was on it's side in a cardboard box. The powder grain probably slid under there when I put it on it's side.

I ordered a calibration weight for the thing... I'll doublecheck it's functionality before I use it from now on.

GGaskill, what I do with the PVC pipe cap is fill it up from the can, then pour it into the container on the scale. It just happens to be the perfect size for my charges. Using it to fill the container on the scale speeds things up considerably. I slow down when it is almost completely transferred and let the scale tell me how much to leave in the pipe cap... usually not more than a 10th ounce. When the scale was acting up, it told me I only poured 2 ounces onto the scale, but the cap holds about 3.7 ounces... I knew something was wrong immediately.

When I started using the PVC cap, I washed it out with dish detergent and left the soapy residue. Soap attracts moisture, so the soapy film eliminates static. After use for a while, the inside acquires a graphite film from the powder, also static eliminating.

intoodeep · « **Reply #5 on:** August 03, 2007, 02:54:57 AM »

Rickk,

Glad you found your problem. I had a similar problem with a battery operated scale I owed in the past. If you weren't real careful when putting the 9v battery in. One of the leads would tend to sneak it's way into the center and touch the weighing platform's pole causing it weigh erratically.

Cat Whisperer · « **Reply #6 on:** August 03, 2007, 04:31:53 AM »

As the Test Engineer, I design and build test equipment to test motors coming off the production line.

There are several variables that we encounter in simple weighing of powder that can be controlled by doing an easy check.

We've noted here that battery level, temperature, humidity and static electricity can affect the results.

Make yourself a SET of weights - 3 or 4 that cover the range of weights that you'll measure powder for.

Make a chart. Each day you use the scale, weigh each of the weights, record the weights in the table.

If each of the weights weighs the same as it did yesterday, the day before and so on, guess what - nothing has changed!

Double D · « **Reply #7 on:** August 03, 2007, 04:47:08 AM »

I have used the bowl and spoon technigue for loading both black powder cartridges and cannon loads. It is slow and a royal pain.

I now use a powder flask and an adjustable powder measure for loads under 120 grains. For loads over 120 grains use 50 Cal. BMG fired case cut down to hold my basic load measure. Well wworth the investment!!

I drop the powder out the flask into the measure filling to the top. I dump the powder from the measure onto the scale pan, then using a standard powder trickler, I bring the charge up to correct weight.

I have never ever had a problem with a grain of powder getting stuck under the pan...but have done just about everything else that can screw things up.

I'll watch for this one.

Rickk · « **Reply #8 on:** August 03, 2007, 06:31:58 AM »

The powder scale I was using is a low profile electronic one, with a platform that is raised maybe 50-60 mils over the scale surface... a perfect distance for wedging a 1F grain under.

Double D · « **Reply #9 on:** August 03, 2007, 06:57:46 AM »

I better stick to mechanical balance, I'll bet I can Murphy's law one of those electronics real easy!!!

Cat Whisperer · « **Reply #10 on:** August 03, 2007, 07:21:03 AM »

Quote from: Double D on August 03, 2007, 06:57:46 AM

I better stick to mechanical balance, I'll bet I can Murphy's law one of those electronics real easy!!!

Mechanical balances have their own set of issues.

Again, build a set of KNOWN weights, keep records, then YOU KNOW you don't have a problem.

m223 · « **Reply #11 on:** August 03, 2007, 11:22:04 AM »

I have to agree with C.W. a calibration weight is about as important as the scale itself, electronic or mechanical. I almost bought one of those powder tricklers at the last gun show now I wish I had. Glad you found your trouble Rickk. Tracy

Terry C. · « **Reply #12 on:** August 03, 2007, 12:27:44 PM »

Quote from: Rickk on August 03, 2007, 12:53:43 AM

I ordered a calibration weight for the thing... I'll doublecheck it's functionality before I use it from now on.

It didn't come with weight(s)?

My Cabelas scale has a pair of weights used for calibration.

DD, I have the same RCBS powder trickler, but I've never used it with black powder because I didn't know if it would be safe (lots of smokeless reloading gear isn't).

Evil Dog · « **Reply #13 on:** August 03, 2007, 12:52:58 PM »

I've always been somewhat suspect of my PACT electronic scale. Have noticed that it does seem to be more reliable when plugged into AC rather than running solely on the internal 9V battery. It came with check weights and I calibrate it before every session.... still just don't particularly trust it though. It seems to "skip" between numbers... like going from 4.5 to 4.8 and I don't remember seeing 4.6 or 4.7... doesn't happen all that often but enough to make me nervious. I just like watching the poise of the balance beam rise when using a mechanical scale with a powder trickler. Will continue to use the electronic scale for 500+ grain charges for cannon but the mechanical scale is more reassuring for charges weighing less than 10 grains. Just my never to be humble opinion.

Double D · « **Reply #14 on:** August 03, 2007, 04:08:24 PM »

The Trickler is made of zinc...non sparking, which is the main issue. It won't crush or cut grains which is the other issue.

I have noticed the same thing with number jumping with the electronic scale.

lance · « **Reply #15 on:** August 03, 2007, 04:37:45 PM »

great info, i see some things i'm going to do.

intoodeep · « **Reply #16 on:** August 03, 2007, 04:51:31 PM »

I have seen the numbers jump around with the PACT scale that I used to have. Mine had to warm up (if not numbers would jump) and I would have to be careful where I placed it too. If, it is anywhere near the draft of an AC or heating vent that will cause it to jump. I always used a balance scale to double check my loads approx. every tenth one. If it did match then I started from scratch. Most of the times the digital worked fine but, once in awhile it had it's off days.

Funny part is one day I got pissed and gave up on it. The wife volunteered to do the measuring and guess what..... I shot the best I ever did with that load. I just think she has the patience....

jeeper1 · « **Reply #17 on:** August 03, 2007, 05:16:53 PM »

Filling the base of the trickler with lead steadies it up some considerable.

Evil Dog · « **Reply #18 on:** August 04, 2007, 06:01:29 AM »

I not only fill the base of the trickler with lead, I also have a 2" long piece of 1/4x20 bolt coming out the bottom. Use it to secure the trickler to the shelf that it on... doesn't move around at all that way. My reloading bench setup has a shelf at eye level that the scale and powder trickler are set up on.

jeeper1 · « **Reply #19 on:** August 04, 2007, 10:35:07 AM »

Quote

My reloading bench setup has a shelf at eye level that the scale and powder trickler are set up on.

Mine too.