Just to explain the "Ratio thing", in layman's terms:
The c:b ratio refers to the ratio of VOLUME between your chamber and barrel. The "ideal" ratio for a propane-powered gun is .8:1 (the chamber is 80% of the volume of the barrel), 1.1-1.5:1 is better for hairspray guns.
It's easiest to calculate the volume of your barrel and then figure out the appropriate chamber size to match, rather than calc the chamber first.
For instance, let's just take your 5 ft x 1.5" barrel...
First we need to calculate the volume of a cylinder 1.5" wide x 5 ft (60"). Here's a very helpful little tool for that: http://www.online-calculators.co.uk/vol ... volume.php
So to use that calc, we'll put in a radius of .75 and a height of 60, inches, which yields us 106 cubic inches of volume.
So, if we want a .8:1 ratio, we need an ~85ci chamber. For a 1:1 ratio, we'd obviously need a ~106ci chamber, and for a 1.5:1 ratio, we'd need a ~160ci chamber. (I rounded all those numbers up to the nearest cubic inch, btw).
If you wanted to use 4" pipe for the chamber....
For a .8:1 ratio, we'd need a 4" x 6.75" chamber.
For a 1:1 ratio, we'd need a 4" x 8.5" chamber.
For a 1.5:1 ratio, we'd need a 4" x 12.75" chamber.
You can use that calculator tool I gave you a link for to figure out the proper ratios for other sizes of pipe, too.
If you're going to use propane, go for .8:1 - 1:1. If you're going to use aerosol fuels, go for 1:1 - 1.5:1.
Having a chamber that's too big for the barrel, within reasonable limits, won't decrease performance, it will just "waste" the extra power being produced by the chamber (basically, if your chamber is too big, the barrel simply can't harness all of the energy being put out by the chamber, and thus the "extra" power is wasted as noise and heat). So it's better to go for a too-high C:B ratio than too low. I use 1.5:1 for most of my combustion guns.
Hope that helps.