couple of questions

Best Surface-to-Air in '70s is a toss-up.

Best P(k) probably from Talos--but, luckily, we have no engagement data to base that upon.

Terrier probably wins from a reliability standpoint (Terrie becomes the Standard later on, in a generic sort of sense).

Next best is probably one of the 5" 54 DP mounts--although those are really just follow-ons from the 'best WWII AAA" weapon, the 1946 3"50 DP.

By 1970, the best anti-air weapon is a squadron of F-4J or the same quantity of F-8.

All naval rifles have tapered barrels--the 16" 50cal are no exception; and those have a lot of taper, along with some "steps" in the profile.

For sources, you can always look to some of the 1/720 kits for those big barrels, even the turrets, as long as you do not get caught up in the turret shapes.

cheers i cant find any real cheap bits i might have a look for some smaller 250 scale guns and made turrets

Straight pipe will not be too good.  Barrels are easy enough to come by. eBay is usually a good place to buy $5 junk kits.

full aa defence really so all of em :)

country doesnt really matter

turret face is fine at 700 scale will it even be noticable if i use a straight pipe?

long range, medium range or short range aa weapon? what country? at the muzzle of the 16" or against the turret face?