Use anything you want; the material doesn't matter. As far as deforming, if you have to drive your pins out with a hammer you have the WAY too tight. I can push all of the pins in on my guns with my thumb and a little pressure, I push them out with a 1/16" punch and slight hand pressure as well.
On my last build the gun started shooting poorly, I checked the pins and found that I had to drive the front pin out with a hammer, it wasn't that way when I finished the gun. I suspect the barrel settled back into the breech just a hair after a bunch of shooting and changed the relationship between the lug and pin hole. I re-drilled the pin hole and slotted the lug a little more, I could push the pin in with my finger again and the accuracy came back.
On my last build the gun started shooting poorly, I checked the pins and found that I had to drive the front pin out with a hammer, it wasn't that way when I finished the gun. I suspect the barrel settled back into the breech just a hair after a bunch of shooting and changed the relationship between the lug and pin hole. I re-drilled the pin hole and slotted the lug a little more, I could push the pin in with my finger again and the accuracy came back.
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