where can I find halachic response/sources for the use of firearms on Shabbos and YomTov
Answer:
The use of firearms would seem to include 3 possible Shabbos prohibitions:
1 The firing of the weapon itself. This involves creating a spark/explosion to fire the bullet, which would be a Biblical prohibition of lighting fire on Shabbos. This would only be permitted in a life threatening situation, when all Shabbos prohibitions are set aside to save a life.
2 The prohibition of carrying in a public domain and from a private to public [and vice versa] domain. The Mishna and Talmud in Shabbos 63a discuss the question of carrying a weapon in the public domain, While this is a matter of debate, the halacha follows the opinion that it is forbidden to carry weapons. See Shulchan Aruch O:C 301:7 and commentaries there. See Aruch Hashulchan ibid. 51 who poses that for a soldier who the weapon is part of his uniform there may be no prohibition. This opinion has not been accepted, see Kovetz Tshuvos [R Elyashiv] 3:51.
3 The prohibition of muktzeh. A firearm would seem to be classified as a "kli shemelachto lissur" an item intended for forbidden Shabbos activity and hence muktzeh. This type of muktzeh may be moved for it's place or to use it for a permissible use. See Shu"t Divrei Yatziv 1:148 who argues that the main usage of a gun is to scare people which is in fact a permissible Shabbos activity. This may remove the muktzeh status from the gun. Being that the scare is based on the fact that it shoots, many still consider a firearm to be muktzeh.