How can I be an effective engineer on Blu team without resorting to the Gunslinger?

From my experience in the Engineer Class I always like to first(even without gunslinger):

1. Choose your inventory right before round start. I dont use gunslinger a lot so I always use the jag as an offensive engineer, because you build faster that other wrenches. Choose a good prime weapon and always be around a pyro (for obvious reasons)

2. Check if there's a area you can pre-build before round starts. If not think right about your inventory.

3. As soon as round starts build a dispenser. Why is that ? You wont need to be running arount for metal scraps, as you have that.

4. Build a sentry and upgrade it to max level. Be sure to have a dispenser near, and put it in a good spot, where it can't be seen and sniped at.

5. Build an entry to the near of your base and the end portal to a flank near the hot spot action ( where your units can flank the opposite team gathered in that spot). If you dont want that, you can always build a teleport from the place you want to place your sentry to the warehouse (where you start). However the last one is more advisable if your team has a weak offense and you need to escape the hot zone.

6. Check your constructions often, and when attacking I dont recommend being alone ( usually go with demo, pyro or heavy), as Engineer is a support class.

7. Don't go too far in the offensive line, except when your team if pwning the other team.

8. Reallocate your construction accordingly to the dynamics of offensive/defensive. What I mean is to be careful where you put your constructions, and reallocate them if you need more attack in one, or if you need to get more people to defend or something like that.

That's all !