Difficulty 4+ (Heresy+) , only good build is Power Sword + Bolter.
every other option is just not worth using, and wastes ammo.
Lasguns, best is the XII DMR Variant, and is no way close to Bolter, cant fight Crusher/Bulwark, massed armored targets, yet also does not have the same or even close DPS of a bolter.
Autoguns? just a huge mess. Agripnaa Braced gun (AK47) is only worth using, but does not match talents or even toughness abilities of the sharpshooter.
Plasma? good in theory, flawed by design.
Bolter, Specials? 1-2 Taps, disablers as mutant/pox hound, 2-4 shots dead, heavy armored target, nearly in 8-12 shots they are dead. massed armored units, a mag is enough.
as for Melee.
Shovel is a decent CC weapon, but single target lacks alot, even its special attack is there just to stun, armored target, as example scab ravager, is hard to take down , same goes for mauler, or any heavy armored targets.
Assault chain sword “Cadia” is the opposite of the shovel, best single target ,yet bad in CC, and as Sharpshooter dont really have a ranged CC weapon, you cant have assault chain sword.
Which leaves you to a single option power sword, good CC and good Single target, only needs time to learn how to use it.
I tried to stay on my build Shovel + Xii Lasgun (DMR) , due that i have a golden one, but yet once i played with bolter things changed alot, same goes to the shovel.