Sourcing weaponry for customisations can be an uphill struggle: there may not be the appropriate weapon in the correct scale for use, or the weapon would fit the look you are gunning for.
I stumbled upon these 1/6-scale modern weapon sets during my usual online browsing, and decided to give them a go. Fans of modern shooting games would recognise them easily, as would servicemen in the military or gun enthusiasts. The kits themselves come together rather easily, building like actual guns (bolts, receivers, the works), and come with magazines, rounds and all sorts of paraphernalia. What's important though, is the fitment.
I didn't expect the weapons to fit so well on MG 1/100 model kits, though they tend to be a little large and can only fit into very specific hand units, i.e., the movable 2.0, 3.0 types that allow the fingers to be wrapped around the handgrips. Even so, a little Blu-Tack is needed to cement the hold.
But they look so gorgeous, especially that Barrett .50 cal Anti-Materiel Rifle!