That is the physics thread cost of moving the object around, you’ll want to manage that by handling how many collidable bodies you have on the gun at the time, it really should never be a major issue unless you are going pretty extreme on component count. For that matter though, you’ll get overlap check costs that are hefty regardless of it being a simulating object or not if you are moving it around with lots of full collision components on it.
You can turn off overlaps, manage collision, or merge bodies to help alleviate it, same as on characters where a large portion (or even the majority) of the cpu cost ends up being in physics thread updates.
I’m going to assume that if its actually something that is noticable to you in profiling that you must have a large component count on your weapon and are running full collision instead of query only or something lighter.