Lyman 500 scale repeatability

Hello,

I bought an old T Mag (not a T Mag 2) kit several years ago and at that time it already seemed decades old (unused, new in box, never opened). The Lyman 500 scale is cast iron not the plastic one they currently
Make.

I have a set of check weights and as I prepare to embark on reloading I have been messing with the scale and my bottle of IMR 4895. I found when I weighed out 40grn and then moved the scales around and tried again it came to a different weight. Using my check weights earlier I found that 41.5 grn weights was 41.2 in the scale which is fine if it is consistent. However, now a couple hours later I am finding 41.5 grains of check weights (the same weights as there is only one combo to achieve this weight) the scale is even at 40.9 grains. 0.3 grains of un-repeatability is too much!

What can I do? The scale is very sensitive and actually settles in the same place every time. I used pencil lead on the knife edges and they don’t seem to be the issue as like I said it will consistently stop the needle in the same place every time with no stiction. Could the issue be with the scale markers some how?

I am uploading some pics - even just taking the photos for this thread, you can see that it is now showing 41.9, a whole grain delta, just after adjusting the scales back and forth.

What am I doing wrong here?

Yes I am bending over to look, my scale will be at eye level once I build my bench in the next couple weeks.
Thanks for the input guys, it might be a couple days before I get back to my office room but I will be checking all the things mentioned above!

dgod said:

Do you have different scale cups (The Brass Colored item)? I have 3 different sets of scales (All RCBS), they make a difference as they are tailored to the specific scale.

Click to expand...

Just the one.

Ok. I am glad I’ve been toying with my equipment while I wait to get fully setup.

User error, of course, is a lot of my issue and I’ve now had 0.1 grain repeatability depending on what surface I’m using (ie my weights are right on on one table and 0.1 heavy on another, with a zeroed scale each time) but definitely not the crazy variations. I attribute this to the above posts but predominantly I was not ensuing the large weight was positively seated in all the way in the groove each time. It does not take much to make a huge change. I’ve been pressing it down pretty good now.

I’ve found also that even a light touch to the top or the bottom of the large weight makes a difference of up to some tenths of a grain even if it isn’t unseated from the groove, where I am pointing with the blue pencil. If I push there, now my weight reads heavier (ie the pointer is 0.5 Cm above the stationary line), but if I push on the bottom, it goes back to reading exactly level (in this case, 41.2 grains with 41 grn check weights installed). Like everything else it seems like consistency will be the name of the game.

Another poster asked if the beam was parallel to the base and it is not as my other photos show.

I am starting to feel pretty confident in this scale after making the chart attached with a consistent technique!