"You can seriously just go off into the forest and shoot?"
Yes, with certain restrictions, notably regarding housing density. The forests are "multi-use," and some private property areas are included. Also, the forest rangers can close off an area for other reasons, such as when it becomes known as an informal shooting area and gun slobs bring up things like TV sets to shoot at and then don't pack their junk out with them. These places become littered with broken glass, abandoned cars, old paper targets, etc. There are also restrictions with respect to proximity to highways and the like. But basically, yes, you can just go out in the forest and shoot.
When I lived in the city of Boulder CO I used to be able to load up five test rounds, drive five minutes up Boulder Canyon into the Roosevelt National Forest, and test the loads. Then I'd drive back home, load up five more with a different powder charge, and drive back up the canyon to test those out. Rinse and repeat.
That particular area was closed because there was a 36" high-pressure domestic water line serving the city of Boulder runnng through it nearby and some schmuck shot holes in it. Prick. Ruined it for everyone else.
"Can non-residents just go buy a gun in Colorado?"
No. With retail transactions, you have to show residency --as is, I believe, asked on the 4473 form. Takes three months' worth of rent receipts, utility bills, etc, and/or a Colorado ID or DL to prove up on residency to vote, last I heard. That's the "Motor Voter" loophole, where you don't even have to prove citizenship to vote. Far more dangerous than the gun show loophole, in my opinion (see below.)
Privately, I'm not sure. I think there's something about having "reason to believe" or "knowing or should have known" the person is a non-resident or prohibited person, but basically, private transactions between eligible persons is not subject to review by the awe-thaur-it-ays. This is the so-called "gun show loophole" you hear about, because private dealers can set up a table and sell privately at gun shows without going through the NICS process. Or they can wander around the parking lot with a gun for sale, last I heard. I don't go to any gun shows anymore, anyhow.
I'm admittedly kind of muddy on those aspects of private transactions since I never sell guns.
"Does the square root of amphibians = bicycle?"
10 LET SQRT(VAL("AMPHIBIANS")) = X
20 PRINT X
>RUN
42
Pretty BASIC, eh?
(With apologies to "The Hitchhiker's Guide to the Galaxy.")
Terry, 230RN