The claymore and the Heartstealer are bigger than the Great axeblade and yet they are all 20 pixels long, this is due to the fact that the pixels of the claymore and the Heartstealer are bigger (and also bigger than all the other weapons of the game and the player's skin ).

To see it more easily, compare the pixel size of the four claymore in the inventory with a weapon that is not a claymore like the sword.

In my opinion, to solve the problem, the solution would be to reduce the size of the claymore and Heartstealer pixels to the same size as the Great Axeblade. Then enlarge by 1 pixel in width and increase the length of the texture of the blade of the Claymore, the Heartstealer, the Great Axeblade and the Broadsword so that they do not appear small compared to the Obsidian Claymore and the other weapons

Or enlarge the pixels of the Great axeblade to the same size as the claymore