Sometimes it takes them an hour or more to sink. In stormy conditions they go down faster, in calm seas or moving slow they may take more time.
Don't hit the same spot twice - and don't go for the bow itself.
Try to hit them there! One eel only!
(in general "under the fore mast" - it opens up two compartments - fore and aft the mast)
The steamers are as good as the electrics to sink a target. You may chose wisely what torpedo and what pistol (and depth setting!) to use according to the given conditions.
Steamers are longer range and faster than electrics if you want. At night the bubbles are no problem. The only advantage of electrics is the lack of a bubble trail. They are slow and have a shorter range by design.
The pistol function is not related to the torpedo type.
Describe the situation you are in.
What are the weather conditions? Daytime? What is your position in relation to the T3? Are you submerged? Are you detected? What other U-Boot is there around? Is the T3 zagging? What is the T3's speed?
How do you observe the result of your measures? Event camera? Periscope?
Do you hover/F12 over to the T3 and watch your eels hit? How long do you wait and observe, until you decide to reload?
And do you play any mod?