Like many model kits, this Tiger from Border Models includes a metal gun barrel. This feature of a tank is difficult to render perfectly in the medium of plastic. A metal version can be seamless and perfectly straight.
But Border's metal gun barrel is less accurate than the plastic one that they also provide in this kit. The reason lies here: a place halfway along the barrel where the outer sleeve is clamped to the inner sleeve by a threaded ring.
To loosen or tighten this ring, you would grip it with a large wrench. And the ring contains two notches (arrowed) where you can insert the arms of the wrench. Of course, to give you the best grip, the notches must be exactly on opposite sides. Such rings therefore have an even number of notches. This particular ring has two notches in every surviving Tiger, and there is no reason to think it was ever different.
But Border's metal gun barrel has three notches.
I cannot suggest why Border would put two notches in their plastic barrel and three in their metal representation of the same thing.