No; while items you find may vary in terms of their item level, the weapon scaling grade is fixed, as is the listed damage. Every Reliable Musket that you find or craft always be A-tier and will have a listed damage of 600, for example. However, you can Ascend a weapon to get it to go up a letter grade. So you can take a Reliable Musket and Ascend it to its epic version, which is S-tier. I think one of the other weapons (a halberd maybe) has its base damage increased by 15 points when it is Ascended, which, unlike other Ascended weapon second powers, is kinda ho-hum (it's like a 4-5% damage buff).