Do I detect a note of sarcasm,Ben?
Cal, the "Short" 2 3/4" mags will not hurt anything except your shoulder. However....
Firing a 2 3/4" or shorter round in a 3" chamber means that neglect in cleaning the chamber thoroughly means a buildup of crud before the forcing cone. This can lead to corrosion, pitting,
and hard chambering and extraction of the longer rounds. Same with 3 1/2" for those manly men who shoot those howitzer loads.
Proper maintenance stops this. A 10 ga brush makes a good 12 ga chamber brush, or the dowel,steel wool and variable speed drill method will also get the crud out.
As for training ammo, I recommend nice cheap and light loads for most of it, and some duty ammo just to check compatibility and zero. Don't forget to pattern.
The short mags tend to be great for proper game, but I see little use in regular practice with same.
Hope this helps....