Hypodermic Tubing Sizes

Since .50 cal is .5" divide .5 by 48 for 1/48th scale which comes to an inside diameter of .010" which would be 22 gauge hypodermic tubing.
I think the heavy-walled stuff from SmallParts.com would be best as it has a thicker wall and looks more realistic. http://www.smallparts.com/components/
For 1/35 scale it would be .5" divided by 35 which comes to an inside diameter of .014" which would be closest to 21 gauge hypodermic tubing.
This stuff is fairly hard as it is stainless steel,but it cuts great with a Dremel tool with an emery cutting wheel on it. Wear your safety glasses though!
There is no way to drill the air cooling vents in the tubing though.
If you want that kind of realism then you need to buy some of the aftermarket machine guns that they sell.

Mike

Awesome! Thanks Mike. I'm going to give this a shot on my next project. I hate when guns have that plastic look, so hopefully this will help.

~ Garth

Try this site if you are interested in barrels with the cooling jackets.

http://www.karaya.ceti.pl/eng/eng2.html

I've used their 1/48 scale barrels and highly recommend them. I'd pass on thier resin bodies however, unless they've drastically improved their molds. I use the kit gun bodies.

50 caliber

Caliber/Scale
.50/72=.0069 29 or 30 gauge
.50/48=.0104 26 or 27 gauge
.50/32=.0156 24 or 25 gauge
.50/24=.0208 21 or 22 gauge
.50/18=.0277 19 gauge

So as not to forget the metric guns, 20mm
The list I have has all the sizes in inches, you can either convert the size now or after you do the scale conversion, I'll do it now to keep it easy
20mm / 25.4mm per inch = .787 inches

Caliber/Scale
.787/72=.0109 26 or 27 gauge
.787/48=.0164 24 or 25 gauge
.787/32=.0246 20 gauge
.787/24=.0328 19 gauge
.787/18=.0437 17 or 18 gauge

The math is the same and very easy, just divide the nominal bore diameter (.50, .30, 20mm, 30mm) by the scale (72,48,32) and you've got it.

There was also a question regarding the calculations being for the bore diameter, in the past when this question came up, most of the time, the person was wondering what the proper inside diameter (ID) of the tube was, you could calculate based on outside diameter (OD) of the gun, but since I don't have a chart of the OD's of various guns, I find it easier to calculate by nominal ID.

For example, assuming a 50 caliber gun has a 1/4" wall thickness in real life, this would make the OD of the gun approx. 1" in real life.

And as an example, we'll use 1/48th scale
1/48= .0208 OD Which is a 25 gauge tube, and does jive with the calculations above.

If the wall diameter in real life is 3/8", then .5+.375+.375=1.25

1.25/48=.026 OD, a 23 gauge tube with an ID of .013, which is close