Horizontal mags are cool, they slide smoother, get stuck less, and sound quieter when loading/unloading.
A big advantage of this is the print direction of the feed lips, which makes them much much more difficult to break when printed horizontally.
Sound example video (vertical print first):
I recommend using support on these three areas, as well as enabling ironing for the mag and follower:
The original 31K-H311 mags can be printed horizontally, but they have some issues and need a lot more supports. I made some quick mods to the magazine to make it print smoother and work better.
These are specifically for the 31K-H311, but similar modifications can be done to other 31K mags. Specifically these changes were made:
The inside walls of the front of the mag were changed to 45 degree angles. (This must also be applied to the follower and plate)
A full slot was cut for the mag release to prevent curved-mid-air-bridging.
The inside of the slot has a bevel for easier printing.
The front of the follower was rounded, and printed laying flat to prevent catching on the slot.
The follower and plate were also shortened slightly to accommodate any droopy overhand inside the front of the magazine.
The author remixed this model.
Modified the magazine components to be printed horizontally.