You are correct. Waterman carts are really a full 1 1/4" longer
WATERMAN: Overall Size - 2 3/4 in. x 1/4 in. (70mm x 7mm)
INTERNATIONAL: - Overall Size - 1 1/2 in. x 1/4 in. (40mm x 6mm)
When you say the international cartridge is 1-1/2" long, I think you are looking at a "short" standard international cartridge. There are two "standard" sized international carts, "short" and "long".
A "long" standard international cartridge (e.g., Pelikan 4001 cart) is 2-7/8" long x 1/4" in diameter at the fat end. So it seems the long international cartridge is actually a tad longer than the Waterman cartridge. (Actually "standard" international cartridge lengths can vary a bit from manufacturer to manufacturer.)
Maybe Waterman cartridges and standard long international cartridges are actually the same?
I attach a (bad hand phone camera) snapshot of some long vs. short international carts that I had kicking around my desk drawer.
So, what happens if you try to use a standard long international cartridge? Is it too long to fit the new Skyline?
What happens if you try to use a standard short international cartridge? Is it too short to be inserted and removed? Maybe that's why you went with the longer Waterman cartridge?
Have you tried a standard long international cartridge (e.g., Monteverde or Pelikan)?
I lament finding out we cannot unscrew the pen where the section meets the barrel. That would make cartridge removal easier regardless of the cartridge size and most importantly, you can check how full the pen is! Right now it seems there is no way to see how much ink you have left without physically pulling the converter or cartridge out.
If the W.E. pen depends on Waterman carts, then please offer some for sale on your site. Waterman cartridges are hard/impossible to find locally.
As it is now, if I want a box of Waterman cartridges for the W.E. pen, I would have to order and ship them internationally from separate vendor. One stop shopping from W.E. would be much better.
Yes, the pen comes with a converter. But there are reasons to have some carts on hand:
1. IMO It is easier to travel with a fountain pen when using cartridges.
2. It is always good to have a cartridge on hand (e.g. in my office drawer or glove box) in case I run out of ink or have an ink mishap.
3. Many times I have found converters to be troublesome - hampering flow, or mechanical issues (Pilot/Namiki converters are notorious). In these cases I just toss the converter and syringe fill cartridges.
While you are at it, it would be nice if you added some roller ball and ballpoint refills too. Some lovely Monteverde and/or Private Reserve refills would be cool.