“There is no law in Colorado to register semi-autos and all mags owned prior to the law are grandfathered. I bought a bunch of 20 and 30 rd mags right before the law took effect.”
Reminds me of what I did in NJ. A friend and I used to go to gun shows in Pennsylvania quite often after Gov. James (”Flim Flam”) Florio shoved an “assault weapon” ban down our throats, including a ban on ANY mags (pre- or post-ban) over 15 rounds. We bought PLENTY of 20- and 30-round AR mags. I never used them in NJ, but when my wife and I left (escaped, really) 15 years ago, I remarked to her (after we passed the “Welcome to Delaware” sign), “Now you won’t have to bail me out of jail.” She was shocked, and asked why, and I explained the law to her. She asked how many I had, and I said, “Well, 18 inches behind my ass is roughly 200 years’ worth in Rahway State Prison.” She turned white and took about 30 seconds to ask if Texas had any laws like that. I told her, “No, Texas is in America.” Thankfully it still is, and I can buy whatever I want that I can afford.
Nothing at all unless they were date stamped like the ones I bought and the date was post-ban. I simply didn't want to wait and since traveling is out of the question for me for the foreseeable future I wanted to have them shipped to me. The pre-ban date stamp should work in my favor too if things go sideways for me. ;-)
We're working here to restore Colorado to America and managed to get part way back.