I know, I know: it's been five years! But there have also been refinements - to virtually all the (ultimately 4x) part(s) in this little set - to provide major improvements:
Click on Image for FULL RES
The accurized barbette (top, left), widened to 550-scale (though Airfix' barbettes were already too narrow even for their own, nominally 600-scale turrets), now has been hollowed to an eccentric oval - permitting slight fore-or-aft repositioning (with the thinnest wall making contact) or, alternatively, perfect centering (with the widest wall contacting), as desired - over the Airfix barbettes without any need to remove them.
Gun barrels, originally just kyped straight from the Airfix Suffolk's 8-inchers as being "close enough", are now being redone right - starting with browsing for more accurate 6-inch bore diameters among Revell's 570-scale DKM 5.9-inchers: from their Bismarck (bottom, left) and Scharnhorst (bottom, twin- and single guns on sprues).
Theoretically, such 5.9-inchers at 1:570 should scale to 5.7-inchers at 1:550 ([550/570] x 5.9 = 5.7). However theory immediately goes out the window upon observation first that neither of the Revell twin-turrets are identical - nor also are any of the gun barrel types. Bismarck's are notably thicker than Scharnhorst's twins, which in turn appear slightly thicker than the single-barrels (with all flash removed), which latter achieve the the best- and very close match with a drawing (not shown) of the RN Twin-6incher in 550-scale.
Therefore - given that the above should look, at 550-scale, like only 5.7-inchers, and the finest of the lot and already look like a full 6 inches - virtually all these Revell guns must be oversized. Thus, a probable additional use for the new barrels developed here, will be to refine/accurize the Revell DKM twins (especially Bismarck's) when the time comes…
In any case, our RN Twin-6inch Turret accordingly will now have its gunports refined/accurized, and given far better mountings for the new guns - utilizing a turret base (top, right), which may currently look a bit rough, but should clean/finish up very nicely, and quickly.
So, stay tuned - for some serious progress - very close to completion, here...