So, I went to check and on my Tiger. The mantlet will not contact the hatch when it is open.
On the other hand, the lower part of the barrel sleeve will hit the periscope head on. I don't think the spring would save it.
I always thought that the body of the periscope (black in my photo) was always bolted to the hatch and that the facility to swing open was to allow the lower and upper prism (or mirror) assemblies to be inserted in the periscope body.
Vince
p.s. In the lower photo, if I try to close the hatch than it will contact the mantlet. The turret has to be traversed a little to the right so that this won't happen.