Well, mine is 320 and I bought it from the shop. I've seen 328. I have a few near-300 value weapons by now that I've gotten through fusing. I'm wondering what the highest is that you have and have seen?
Surely, someone must've played it so much that they have a 400+ value weapon....
Read the mania: http://www.fanfiction.net/~nonexistinghero In SA2, it's Super Sonic and Hyper Shadow.
I got a Bowl arm with 340 from chapter 4 on 8.0 intensity! fused it with a 337 weapon to make my new best weapon, a 337 Divine Bow with 5.5 range and 1 melee star, overall def. +4, health +5, weakening +1, shot homing +1 and standing cont. fire +1.
If you think you are good at something, there's an Asian on YouTube better than you.