This is what I've always been saying, though. It wouldn't be hard to design these new weapons in a way that gives them a separate niche to fill in the game so they serve different purposes.
.38 Revolver: More powerful than the .38 Pipe Revolver, with range and accuracy comparable to the .44, but not nearly as modifiable as the Pipe Revolver - which can be chambered for different ammo types, converted into a rifle, etc. Plus, we need a .38 weapon that isn't a pipe gun, and the .38 revolver is pretty iconic.
.44 Lever-Action Rifle: Harder hitting, slower firing, and lower range than the Hunting Rifle, plus it uses a less common ammo type and gives another purpose for .44 ammo.
.50 Elephant Gun would serve the purpose everyone complains that the .50 Hunting Rifle fails to serve - a hard-hitting beast of a gun to put down Behemoths and Mirelurk Queens. I'm thinking single/double shot instead of a magazine, and absurd recoil. I say Elephant Gun instead of Anti-Material Rifle like other peeps because we already have a ton of militaristic weapons.
While we're at it, a .44 Desert Eagle that behaves like a 10mm but hurts like a .44 Magnum (with a little less power, so as not to completely outclass the revolver) would fit in nicely. And a pump-action shotgun is probably my top request for new guns.