changing that would be nice, although priority is not "high" as its not affecting gameplay

It affects realism however. Just one of the many things that needs to be fixed.

During the Alpha stage, visual related stuffs that are not gamebraking shouldn't be labeled as HIGH PRIORITY.

A HIGH PRIORITY visual issue would be corrupted textures on buildings, but certainly not a mag that should be "bigger" and it's not.

But they are not the same size. The 100 round magazines are twice as thick and slightly longer.

The magazine you are talking about is the surefire 100 rounder, google search it. It is a little longer and goofy looking. I would recommend loosing the 100 rounder and either go to the smaller 60 rounder which this 100 rounder in game depicts or go to a drum. Nobody in the military will ever use the 100 rounder, how are you going to get in the prone? Check out this picture of the magazine. Also look up the 60 rounder.
http://www.shootingillustrated.com/wp-content/uploads/2011/01/Surefire-mags-2.jpg

it is 3x so large at the sides, so its like a tripple magazin. by the way, dont try it on the standart MX, cause the visualized magazin wont change, try the MX AR and compare them

Edited title for clarity.

In general the problem probably is that weapon magazine is still a part of weapon model instead of being separate entity.

The related issue with large pistol mags is reported here: #4287. Removed that part of the description to keep the report clean.

They dont have the same size.

It would be really nice if the magazine was just another attachment to the rifle/pistol

Not a problem anymore, since mags are not part of weapon 3d model anymore, but are separated from it.
@Astaroth ticket can be closed.