[Pistol Amp] affect [Mesa]'s exalted weapon
Why rank 8 [Narrow Minded] and [Vitality]? Because this build intended for new player and rank 8 is enough for now and you can allocate your endo and credits to upgrade another mods. [Mesa] 3rd ability can [Reach] its peak with 119% strength.
How to use: 3rd ability for damage reduction, 2nd ability for more damage, then 4th ability to shoot enemies till they die (hold your fire button and enemies should be inside the reticle). Reset 4th ability when the reticle too small
You can get [Narrow Minded] from Orokin Vault

Here is a build for Mesa's Regulator