Replacing 1/350 5" guns to fit scale

If my calculations are correct. A 5" gun in 1/350 should be approx. .01428". Which in turn comes to 28 gauge thin wall hypodermic tubing, according to http://www.smallparts.com/products/descriptions/htx%2dtw.cfm
As for working with hypodermic tubing? You could cut with an abrasive cut off disc in a Dremel (be sure and wear safety glasses). As for attaching the tubing? You can use super glue or epoxy.
I have never built a ship model before but, if it is possible, you might try and drill out the turret, where the barrels attach and cut the tubing a little over-length. It may give a better foundation for the tubing once glued and inserted.

Best bet is just buy the L'Arsenal replacement guns.

Thanks Guys!
L'Arsenal has some nice things, but MAN are they pricey. At $19.00 just to charge with
your bank card, I'm leaning towards the small parts guys. Chopper, did you use your
conversion at 5" (inside barrel Dim)? I figured 9" diameter outside barrel Dim at .0257
Is my math correct on that?

Thanks for both inputs.

Yes, I figured ID. And yes, your math is correct.
DOH!!! I just noticed why you are questioning my figure!!! My apologies.
If you go with the thin wall tubing, you would go with the 24 gauge. The ID would be very close but, the OD would be off.
If you go with regular wall tubing, it would be 23 gauge. Then, it would be just the opposite. The ID would be off a little but, the OD would be closer.
I was looking in the wrong column when I posted earlier.

Don't worry, I'm keeping my eye on you Chopperfan. [: D]
I didn't realize they even had different wall thicknesses.
Maybe I should just go with 23 or 24 guage regular wall.

Thanks again Ron and Chopper for your suggestions.