I'm having a machine shop make me a few various parts for my glock that will have medium to high wear. What kind of metal should i have them use?
Sorry I can't really answer your question, but why?
There are hundreds of Glock distributors online that will sell you Factory parts for a few bucks. Are these custom parts that you're trying to enhance your Glock with?
Just realize that when you install these machine shop parts that will completely void your Glock warranty. I don't know if even Glock, the king of Great customer service, would back up there product if it had home made parts in it.
I'd call up Glock and ask them about the quality of the steel used or head over to GlockTalk.com if you don't get what you need here. There are a lot of knowledgeable guys over there.
And if you are a competent gun smith/designer, my appoligies.