I am sorry reaper. I saw your characters, everything is A okay. =) welcome on S.S madness. 

Casting alchemy through weapons would be like, say you engrave a sigil on a bullet and fire it through a sniper. You cover a large distance and accurately dmack that bullet where you want, upon contact the sigil ignites amd boom. 

However the weapon in no way makes the alchemic output stronger by channeling.

You see the norm of weapons in amro is so that asylums dont focus too much on alchemy. Thats why they have anti alchemy and their technology is a 100 years advance. So they have plasma technology and many others.