SchoeppSwanson

Make an animation with the weapon where you want it, apply the appropriate mask in cfgmovesbasic. Add a script that plays that gesture when you want it.

The way the animation system in Arma 3 works is action -> stance -> animation. An action triggers the need for an animation, it then references a config file that corresponds with the current stance, and then it plays that animation. So lets say you are reloading an M16, then you instantly go prone. Your spine will be broken backwards, as the animation for reloading while standing up has a different position than the animation of you reloading while prone. However, your stance was changed after the animation was called. This is why you can start a reload animation for a machine gun, then get in a helicopter and you'll keep doing it until you are done. Unlike other games, Arma 3 does not have the ability to tween inbetween different animations of different stances smoothy. That is to say if you are on frame 60 of M16 reload animation while prone and you stand up, you'll be on frame 61 of the standing variant of the reload animation (or however many frames pass while you get up). Its part of the reason why animating for Arma 3 is so tedious. Instead of making one single animation that can be played with any stance like in COD or having a couple like standing and prone like BF, you have to make one for each major stance, else you have irregularities. Unless you are fine with them of course.