I did a couple as the Panther Coelian Flakzwilling 44 but replaced the resin barrels made in the same way as the Super Coelian guns.
Here are a few shots of the turrets with the replacement metal barrels for both the Coelian and Super Coelian.
I made the barrels by using lengths of normal domestic pins cut to the required length (snipping off the head and point with pliers). The muzzle pieces I cut from a length of tubing I had from a model shop. I cut the pieces off with a junior hacksaw as a saw makes sure the tube is not squashed. It then needs to be filed to be flat at each end (given the pieces are small the exposed end needs to be filed before cutting a piece off then it is glued on the end of the pin piece with the newly cut end showing so it can then be filed more easily). The tricky bit is drilling into the resin to glue in the new metal barrels - it just needs the right size drill bit and a very slow careful drilling action making sure the bit starts out in the centre of the resin part of the barrel as it is not that much thicker than the pin.
A couple of comparison shots of the Panther Coelian Flakzwilling 44 with the original resin barrels and with the replacement metal barrels. The resin barrels are slightly wonky but also rather fragile so I am much happier with the metal replacements.
In case of interest, links to my other experimental and prototype tank posts:
T28 super heavy tank (USA)
M6A2E1 heavy tank
Boarhound armoured car (Shapeways)
TOG 2 heavy tank
T44/ 85 (full platoon)
Prototype Tiger 1, Ausf H2
Dicker Max and Sturer Emil
Panzer VII Löwe (Lion)
JgPz E 75 "Jagd Panther II"
Panther Coelian Flakzwilling 44
E75 standard tank (Tiger III)
For an easy way to see all my WW2 posts check out the WW2 Summary page.