Dating (approx) a Colt AR-15 .223 magazine

[KOPBET]

I have an aluminum 20 rd. Colt magazine with no markings other than the UI (CH) stamping on the side. Stamped, folded and welded on the spline. Has an aluminum follower and has a strong spring.

I'm guessing it would be prior to 1969 since Colt marked it CAL .223 but I have little knowledge of actual timelines.

Like this image from AR15.com:

Is it worth anything above $40?

Any help appreciated.

 

[WoodsCraft]

It looks like a commercial magazine that came with a sporter. Could be 60’s-70’s vintage

 

[Swingwing]

Check these links out. Looks like a bunch of info,

Development of the AR-15 Magazine and Photo Resource Thread - AR15.COM

Firearm Discussion and Resources from AR-15, AK-47, Handguns and more! Buy, Sell, and Trade your Firearms and Gear.

www.ar15.com

Fulton Armory FAQ: The Lowdown on AR-15/M16 Magazines