thanks for the comments guys - the .50cal is part of the Aber etched set, which contains more parts than you shake a stick at. My .50cal doesnt even use them all because frankly you could spend a full build detailing the gun alone!
the pistol port is glued into its kit position so I guess I've fallen foul there. I can try and wrestle it out. I have pics of several t23 turrets and I still missed it

I'll pack the port itself out higher and then build up the frame with putty as suggested.
I also have to adjust the rear brushguards a little - and add a thousand little weld lines with putty. Since the pics were taken I've also drilled out the pickaxe head, which I'm surprised noone spotted

lol
watch this space...