Think of tsuki not as a punch but as a thrust as from spear or sword.
What Janet said. Tsuki is movement through
the front-to-back plane of the body.
I'd highly suggest at this point not
to focus on knives and guns. Focus on your own body, and its relationship to uke in terms of space, position, rhythm, breathe - and learn and experience new ways of moving.
If you want to get off the line (or redirect the line), unbalance uke, apply an atemi... All of that is contained in a single, properly executed irimi movement. It's all the same thing. One movement. Case closed.
If you can't do that first, then all the other subsequent movements are not only irrelevant, they're not aligned and integrated with an effective initial entering movement. In other words - even in "puppy play" language - you're dead.