I like the idea of distant sapper removal, but thats quite powerful, so maybe something like:

-75% ammo (normal pistol has 200 ammo)
-75% fire rate
Sappers do 15% more damage to buildings
and as with the R-Ranger, marked for death when hauling buildings.
speeding up building is too much i think, that'd make the wrench useless.

The sapper idea is cool, but you'd have to slow down the fire rate and make less damage

Pros:

+10% Damage
Alt fire: fires a short-ranged burst of fire which burns enemies and takes off sappers, but takes up one clip

Cons:

-35% Firing speed


It'd be a nice anti-spy weapon

+15% firing speed (+)
+50% clip size (+)
Alt-Fire: Removes Sappers, but removes one full clip (+)
-50% less max secondary ammo (-)
-15% damage penalty (-)

Fires projectiles that repair friendly buildings or damages foes. Basicly a secondary version of the RR. ??% slower fire rate, ??% more accurate, ??% less spare ammo, and ??% more damage. RR is pretty balanced right now, as it trades spy/sapper killing effectivness for more building durability against other classes. Having both a shotgun and a pistol version of the RR would be unbalanced tacticly, as you would only be able to take down a sentry with an ubercharge (quickfix or invuln) or a sapper, not to mention that people who equiped both would have sentries garranteed to survive almost anything but a ubered demo using stickys, nearby heaves useing a minigun or a sapper.

give it the snipers bow pin to wall visual too

Here's my two cents:

Alt-Fire: Removes sappers on all buildings at 150 metal cost
-88% max secondary ammo on wearer (reduces max ammo to 32, as much as a scout)
-20% fire rate

Would make Engineers less afraid of wandering away from their buildings to help their teammates, allowing Engineers to not have to turtle their nests in fear of spies. This would be balanced in the sense of making it less useful for spychecking (and combat in general).

My idea:

+/-) (description) Fires rivets that increases the amount of damage enemies take up to 100% (10% more damage taken per rivet, each rivet lasts 5 seconds in a target, projectiles act like the syringe gun)
+) (hidden) Rivets have no damage falloff (still have base damage of 15
+) No ammo required (I'll explain why down there)

-) No random critical hits
-) Per shot reloaded: -2 metal (use metal to reload weapon, 24 metal for a full clip)

The build up of damage can stack with the weapon, so hitting 10 shots into a target means the target will take double damage from all sources for 5 seconds! This insane supportive ability is offset by the metal used for continously spamming this weapon. In conjunction with a sentry or a mini-sentry, you can make sentry targets take increased damage by hitting the awkwardly firing rivets in your target.
Let me know what you think!