**Why do the pistols and rifles not have trigger guards?** *Because that is by design* and not just because they do not want to animate it. Also, not all firearms in the anime do not have trigger guards. [![enter image description here][1]][1]

I've yet to watch the anime but this was one of the images I found when searching for firearms in *FMA:Brotherhood*. In [Wikipedia][2], real guns can have no trigger guard so

> as not to impair use with large cold weather gloves on, especially those intended to be used in arctic conditions. 

While this might not be in arctic conditions, the fact that some characters in the anime wear gloves proves the point that *this is for ease of use*. It would be difficult to press the trigger with a trigger guard if you have gloves on, especially large and thick ones.


  [1]: https://i.sstatic.net/WDEOy.png
  [2]: https://en.wikipedia.org/wiki/Trigger_guard