A lot of things can cause inaccurate readings on both balance and electronic scales. Air movement, heat effects, dust and 'grit' (they should never get THIS dirty), static electricity, and humidity are all culprits.
Believe it or not, the slightest air movement can cause a scale's reading to fluctuate. Air movement can be the result of drafts, heating vents, fans, and even the motion of people or pets.
To solve this problem, close the door and windows to your reloading room, and also close off all heating vents and turn off any fans when you measure powder. Learn to limit your motion, and avoid making large, sweeping, or abrupt motions. You would be amazed at how the air motion created by just your body motion can affect your scale.
You may want to consider building a protective box over the back, top, and ends of your scale to keep dust and errant breezes away. Of course, you must leave the front open so you can get to the scale - unless you put a transparent door on your box. A friend of mine has one of those clear plastic boxes that are used in chemistry labs to house precision scales. Needless to say, he has NO problem with air movement disturbing his scale. Personally, I have not found a need for one of these.
On balances, uneven heating can cause the beam to expand or contract unevenly, destroying the delicate balance in leverage because one end is longer than the other. On electronic scales especially, the unit must be allowed to 'soak' at the room temperature until it has stabilized. For this reason, it is a good idea to store your balance or electronic scale in the room in which you intend to use it, if at all possible.
Dust and/or grit in the pivot bearings of balances can cause unpredictable or erratic readings or movement. Most of the 'grit' I've experienced tend to be flake powder granules. Aside from accidental powder granules, you can keep your scale clean by, not surprisingly, storing it in a clean, closed space and/or using a dust cover.
Clean the scale pan, beam and bearings with a soft cloth or brush, using an anti-static cleaner like one of the computer screen cleaners or electronics cleaners available at computer and electronics stores. Dust is actually attracted by static electricity (see below), so getting rid of static charges is an important part of keeping your scale clean.
Take a look at your television screen - notice the dust? The reason it accumulates there is because of the static electric charge buildup in your picture tube. It literally pulls in the dust.
Pay special attention to the nylon bearings and balance pivot pins when you clean, as this is where dust tends to accumulate. I like to use a small hobby paintbrush, a cotton swab, or compressed air to clean the nylon bearing surfaces on my scale. NOTE: Always be careful with plastic parts when using solvents of any kind.
Static electricity (either natural buildup or from the smokeless powder itself) can cause errors, especially with scales that have plastic pans or when you're handling plastic tools - like powder funnels. Good balances are magnetically dampened, and static electricity may have adverse affects on this feature. I can only imagine the bad things that static electricity will do to an electronic scale!
To get rid of static, clean the scale pan, beam and bearings with a soft cloth or brush, using an anti-static cleaner. AGAIN - pay special attention to the bearings, as this is where dust tends to accumulate, and be careful with plastic parts when using solvents.
You may consider running a small grounding wire from the scale frame to an electrical ground or get an anti-static mat (don't forget to ground the mat) on which you work.
Humidity can change the density of your powder from session to session, especially if you fail to leave it in a sealed container (the original container is best). I wouldn't think that humidity would affect a balance, but it may affect the workings of an electronic scale.
Always use powder fresh from a sealed can, and always return the powder to the sealed can immediately after finishing your loading session.
Be sure the poise weights are set precisely in their notches when you weigh powder. If in doubt about a charge or reading, dump it back in the hopper.
Be sure that the same person throws all the powder charges if you are using a powder throw. Different people will throw different weights of powder, due to varying techniques and forces applied. Keep your charges consistent by having ONE person throw all the charges once your powder throw is set.
You should always carefully level and re-zero all scales before EACH use, and check with a known check weight from time to time. [If using a powder throw, check the weight of the powder thrown every 10 or so loads.] Buy a check weight set (some electronic scales come with them - mine did) or use a good match grade bullet as your check weight. Record THAT one bullet's weight in your reloading log book (you DO keep one, right?) and put it in a safe place to be used just for the purpose of checking your scale or balance.
By following the techniques that apply to you (I don't have or need an anti-breeze box, for example), you should get very consistent measurements - assuming you're using a quality scale. However, don't get upset if you weigh the same charge two or three times and get slightly different readings each time. A variance of 0.1 - 0.2 really will make no difference in the pressures and accuracies in most cartridge cases unless you are loading very small cases - like .25 or .32 ACPs. These cartridges and their associated firearms are not known for extreme accuracy anyway.
Last updated : 03 January 2000