Powder weight inconsistent

[huntandjeep]

Loading up some ammo for my 7mm. The rifle builder came up with a load that would clover leaf 5 shots @100yards. I used them up and loaded up some more with different results. Had some time today to pull apart my existing ammo and re load them . Problem is I can't get the same weight every time. I zero out my RCBS 505 with the brass pan , throw a charge and trickle in a few more kernels to get my powder weight. Dump it in a case , pour it back into the pan and re weight it ( to double check myself ) . now I have to remove a few kernals ( lets say 4 ) of powder. Get it back to my weight and dump it in the case. Pour it back into the pan and now I need to trickle in 10-15 kernals ? The powder is IMR 7828 SSC. If I move the weights on the scale back to zero I have to re level my scale ( even though I haven't moved a thing ). What am I doing wrong ? Thanks Allen

[Bill W]

Was the scale or arm dropped?  You need to check the pivot point and make sure it's not loose or has a ding on it.  Somethings off and balancing it out and then using the check weights for a number of measurements might let you id what the problem is.

A 505 should be a manual balance scale.

[jasnt]

I have had to clean the pivot point on my scale before. Same issue I was having. Cleaned everything up good and it's weighing as it should

[huntandjeep]

I can't see any large chunks of dirt in the pivot ( I keep it stored in the box ). Took it apart wiped it all down put it back together and same thing. Scale has never been dropped.

[jasnt]

Call rcbs. Bet ya they send ya a new one.

[300rum]

Tell us where you are loading.  On the kitchen table?  In the garage with the door open?  Air conditioner on?  Are you taking the scale from a cold garage and then bringing it inside?

I have had these things affect my scales at times. 

Maybe I missed it but what do your check weights say when you put them on?

[huntandjeep]

Tell us where you are loading.  On the kitchen table?  In the garage with the door open?  Air conditioner on?  Are you taking the scale from a cold garage and then bringing it inside?

I have had these things affect my scales at times. 

Maybe I missed it but what do your check weights say when you put them on?

Loading in my shop , doors closed. Scale stays in the shop. I don't have check weights.

[CP]

I've never had much luck with a balance scale - You might give one of these a try:


http://www.amazon.com/dp/B002BDOHNA/?tag=googhydr-20&hvadid=77828088564&hvpos=1t1&hvexid=&hvnetw=g&hvrand=15384481953746436620&hvpone=&hvptwo=&hvqmt=b&hvdev=c&ref=pd_sl_6vffwe63qd_b

[300rum]

You really should have a check weight, it just helps you find out when something is 'off'.

I have used the above Frankford Arsenal Scale, it is very susceptible to atmospheric changes.  If you use it, make sure that it stays in the same room that you are using and memorize the 'negative' weight of the pan (the number when you take the pan off the scale), it will help to tell you when something is off.   

[Bill W]

the check weight is then the issue.  Either that or weigh a light sinker.  Weigh it 10 times and see how many times the weight varies.   That will help you zero in on your problem.  Your scale is not repeatable the way you are using it now.

[Evil_EdwardO]

Anything close that is causing static electricity may be the issue too. Any type of plastic wrapping, styrofoam or even the powder containers can cause static electricity and throw the balance scale off.

[huntandjeep]

So on the check weight does it have to be a known weight , or could I just use a 168 grain bullet ?

[Bill W]

So on the check weight does it have to be a known weight , or could I just use a 168 grain bullet ?

as long as it weighs the same everytime you weigh it.  If it doesn't there's something wrong with the pivot beam or how your scale is set up.

[CP]

So on the check weight does it have to be a known weight , or could I just use a 168 grain bullet ?

A check weight is a known and precise value, handled carefully and never touched by human hands least it become contaminated with oil or dirt.

Bullet weights on the other hand can vary quite a bit.   

How precise do you want to be?

[Bill W]

who cares what the object weighs?  This is a manual scale, not an electric one.   As long as the same item is weighed every time it should weigh the same.   Let's not focus on having a check weight of known value.  If it is weighed 10 times it should come in at xxx.x every time.    If it doesn't weigh the same every time, then you have an issue to focus on.   The bullet weight will be "precise" once it is weighed to know its number.

What needs to be focused on is not the uncertain weight of a bullet, but the reliability and repeatability of the scale once the bullet weight is determined.

[wadu1]

I use a electronic scale similar to the one that CP suggested, I also use a check weight every 5 0r 6 rounds. I live near the Sound and the barometric pressure is in flux all the time. So my experience with balance scales have been a bust, have gone thou 3 (RCBS 5-0-5, LEE or Frankfort) none were consistently accurate. 

[Fl0und3rz]

So on the check weight does it have to be a known weight , or could I just use a 168 grain bullet ?

Ideally, yes, it should be a known weight, which is verified by a more accurate and a more precise measuring tool, to an error smaller than your balance is supposed to be (+/- 0.1 gains, right).  So your check weight should be its certified weight with a tolerance less that +/- 0.1 grains, such as +/- 0.01 grains, etc.  I think bullets are routinely +/- 0.5 grains or more, at that weight.

So while you can check repeatability (precision) by grossly checking with an unknown weight (Is it 168.5 grains? Is it 167.5 grains? Etc.), it will only tell you if you have repeatibility problems, at that unknown weight (or comparative weight to the balance weight positions) and not if you are getting an accurate AND repeatable/precise weight measurement. 




Also, if say you have some sort of crusty, cobwebs, or some other sort of friction at the fulcrum of your balance, effects on repeatibility may be different at low weights versus higher weights, as higher weights would more easily overcome any friction added to the balance.


So if you want to check repeatability with an unknown weight, do it around your charge weight to have the most value.



Now, all that said, let's go back to your problem description.

I zero out my RCBS 505 with the brass pan , throw a charge and trickle in a few more kernels to get my powder weight. Dump it in a case , pour it back into the pan and re weight it ( to double check myself ) . now I have to remove a few kernals ( lets say 4 ) of powder. Get it back to my weight and dump it in the case. Pour it back into the pan and now I need to trickle in 10-15 kernals ? The powder is IMR 7828 SSC. If I move the weights on the scale back to zero I have to re level my scale ( even though I haven't moved a thing ). What am I doing wrong ?

I don't think you are doing anything wrong other than over-correcting for perceived inadequacies of your equipment. (Yeah, go ahead and make jokes.)

As you trickle powder in the pan, you approach the balance point gently and gradually from the lower side of your target.  When you recheck, you are dumping the powder in the pan, and the indicator/beam might oscillate above and below the target, until it settles. In the process, the approach to the balance point (where the pan and charge weight balance the beams and weights position about the fulcrum) might be different each time and certainly different that trickling to an end point, resulting in some minimal errors. Google hysteresis. 

Add to that that there might be a few kernels remaining in the flash hole, you might have spilled a few, etc., and it begins to look like you have bigger problems, even though it may be your technique that is causing you to think you have problems.

I would expect to have to re-level the scale after putting the beam weights back to zero as even a minute change in scale position might show a 0.1 grain or more difference in indication. 


In my experience, my Redding #2 might show +/- 0.1 grain from charge to charge.  If I put the powder from the pan, into the case, back to the pan, back to the case, I would expect that I might lose powder along the way, bump the scale, a wind might break (don't look at me), some grains might stick to the pan, the funnel, the case, especially with fine powders, etc.   


You are talking about 20 POWDER grains (of essentially what appears to be a relatively fine ball powder) on a charge of 59-63 grains.  How many grains does it take to register a 0.1 grain scale movement?  If it is more than 20, you are making work for yourself attempting to achieve powder measurement accuracy and precision beyond what the scale can produce.


Repeatabilty in technique in powder dispense and measurement is more important with imperfect loading equipment (which means consistent loads, whatever the charge) than to absolutely know you have 60.20000001 grains of powder in each in every load (which can't be done with common reloading equipment, anyway). 

 

[huntandjeep]

OK had a chance to weight 1 140 grain Berger 10×s. Zerod my scale , weighed bullet came up with 140.3 grains 10 times. Removed the bullet slid the weights back to zero added the pan and everything was still zerod out  .