I started looking into anodizing and found that there are several types.  Does anyone know what type Bushmaster, Oly Arms and Colt use?

Hard Anodize (MIL-A-8625E, Type III, Class 1 & 2)

It *must* specify Type III (there is also a Type I and II).

For information on types and classes, try this page:

[url]http://www.techplate.com/hard_anodize.htm[/url]

And this one, which is not the milspec:

[url]http://www.techplate.com/anodize.htm[/url]

Apparently it is now MIL-A-8625F (instead of E), must have been updated some time ago.

Please note that I am not saying which type Bushy and Oly use, only that this is the milspec. If they claim to be milspec, this is it, otherwise it's one of the others (I, IB, II, etc).