[bob1nelson]

on a series 70 or 80 1911 45, when replacing the barrel is there any 'fitting' that needs to be done? [prolly a stupid question, i know]

 

[dfariswheel]

This depends on the barrel.
You can buy "drop in" barrels that usually drop right in a Colt with normally no fitting needed.

If you step up to a Match type barrel fitting is needed, or if your gun has a fitted barrel bushing even a standard barrel may need fitting.

Usually as long as you're installing a name brand barrel in a Colt and it's a drop in type, you should be able to just install it.
If you buy a cheap or "no name" barrel or have a non-Colt gun you may have to do some fitting even with a standard barrel.