Why would 40-65 cartridges Be of different lengths?

These all came from a box labeled Rem UMC 40-65 for Winchester and Marlin. However, the two examples on the left are marked Rem UMC and the two examples on the right are UMC marked. All are marked 40-65. Why would they be of different lengths? Thanks!

The bullets in the UMC are not seated to the crimping cannelure on the bullets.

I’ll be if you weight them or listen & see if you can hear powder inside the two UMC will be light & they look to have been fired judging from the case cannelure & hard to see the base to tell if swelling

Edited once

My question:
Is it my eyes or the angle the first picture was taken, (or both), but the two on the right look to me like the cases are slightly longer than the two on the left… ??

I can’t believe that I didn’t see the bullet length before. The case is the same size - I broke my only calipers but hopefully you can see it in the photo. I can hear powder in both the UMC and the Rem-UMC cases. My rudimentary scale has the UMC weighing in between 449 and 450 gn each (4) and the Rem-UMC between 440 and 442 gn each (16).

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As these are smokeless powder loads the roughly 10 grain difference could be in case, bullet, powder type/brand charge or all three factors. The case cannelure on your UMC looks blown out a bit
Also if you try to hold the bases together so they are in the same spot then look up the case at both & see if the UMC head is any larger than the REM-UMC you might see some swelling, since you can’t measure the head a little up from the rim.
Here’s the same headstamps the UMC is the lower & it has a impressed U on the primer, so you can see the case cannelure,

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The UMC definitely look a bit blown out/swollen. Here are more photos with 6 examples of Rem-UMC and 4 examples of UMC. With the latter you can really see the swelling in the middle two cartridges. Reloads?

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That would be it, re loaded

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And it looks like they person only belled/sized/crimped the mouth, (and perhaps 1/2 to 3/4 inch?), of the cartridge enough to hold the bullet, in order to extend the life of the brass, presuming it was shot out of only one chamber.

Overall length is important if firing in a lever action repeater, but if firing in a single shot, not at all important. (As far as functioning, but may make a big different with the internal ballistics.)

Thank you for the replies!