Identical Kerr Jars Are Not the Same

It's nearly time for me to get rid of a bunch of fine tobacco that I do not really like, so I started going through my "pass" box, collecting everything together to post some jars for sale on here. Most are de-tinned tobaccos stored in 8oz Kerr wide mouth mason jars. I figured I could keep them shut and just weigh an identical empty jar with lid and ring, and then just weigh all of the other identical jars with tobacco in them, and subtract the tare weight from the total weight of each one. Simple, right? Well, I didn't notice a problem until I decided to add a final few jars to my list, one of which had been smoked out of considerably, but I still wanted to move it along. Most of the others had maybe a few bowls out of them, so I didn't really question it too much when a couple jars had already come up with more than the posted tin weight by a couple grams, since I know some manufacturers have been known to over-stuff the tins. So when this last-minute addition came up with a tobacco weight of 51 grams when the tin weight was 50 grams to start with I knew something was odd, since I know I smoked about an ounce of it already. Checked the weight of a few lids and rings, and they all seemed to match. Then I checked a couple other empty identical jars, and they matched up too. (Scratches head.) Then I checked zero on the scale and weighed a check-weight, and that was all good. Then I dumped out the tobacco and weighed it directly, and that came out to 20-something grams, whatever it was, but that confirmed that something was up. I weighed the jar that the tobacco came out of, and it weighs 185 grams! The other identical jar weighs 207 grams! These are the same jars in terms of sku number and outwardly look the same, same text molded in, came out of the same-style boxes, but the form of one is actually slightly different on the concave bottom and along the edge transitioning to the side, and the bottoms of the lighter ones have a bullseye appearance within the glass, and the heavier ones are smoother. Then just out of curiosity, I gathered a few empty jars of both versions and compared the variance between the same version, and there was a up to a 5g swing across a few of the same version, which I thought was a lot too, but obviously that is just the manufacturing tolerance for one version or the other. Now I get to go back and weigh each actual tobacco. Glad I noticed this before I posted a new sales thread. Imagine if I had sold someone a jar of tobacco and it was 50% light, or light at all. Note: This does not affect anything that I have sold from my sales thread already posted, do not worry if you bought anything out of it, that tobacco was already being hand-weighed individually to order. ::

Obviously this is only a problem if you don't know the actual individual jar weight, or actual tobacco weight, and you don't want to open the jars, and you want to be sure of the weight of the tobacco. For inventory, I could identify the jars based on the faint bulls-eye pattern in the glass on the bottom and just allow for the 5g slew. I mis-typed above, one of the heavier jars had the ~1oz of tobacco in it when I noticed the problem, but you get the idea.

If anyone is trying to follow the math(s), my tare that I started with was 205g, which was a lighter-version jar plus a ~10g lid and ~10g ring. ::

Fortunately wyfbane, I only have 15 or 20 de-tinned jars that I want to move along.
Pagan, I was not all that surprised to see the 5g variance between jars of one version or the other, although I thought even 5g was a wide enough margin for me to re-weigh everything. The biggest difference came from the two different versions of the jars that basically looked almost exactly the same, save for the faint bulls-eye pattern on the bottom of the lighter-version jars as well as a slight difference to the concave shape of the bottom. It's hard to describe, and both versions have smooth bottoms, but if you look at the lighter-version bottom, you can see a bulls-eye pattern within the glass. After thinking about it, those are probably air bubbles, perhaps intentionally injected to save cost of material. There was a ~20g difference between the jars with the bullseye pattern vs. without.
McTinner, hopefully the difference was to your benefit.
jpmcwjr, I think the words directly above should explain the answer your question. ::

Jay,
I feel like sometimes I do that, and the forum software just runs it all together anyway. I had issues with spacing out text in my sales thread, and could not finish editing it in time, so just resigned to editing in an apology during the last few minutes of editing time.
I had a chance to look more closely at the jars, and the bulls-eye pattern on the bottom of the lighter-version jars are actually faint waves on the outside surface of the glass. You can see them pretty easily, but it is tough to feel it. The weight difference in any case is in the thickness of the glass bottom. The lighter version has the bulls-eye and a noticeably thinner bottom when compared with the heavier version in a side-view, and you can also see slight differences when comparing like-versions (bulls-eye or non-bullseye). Perhaps that pattern strengthens the thinner bottom.