That tennifer/nitrocarburized finish can be hell on a tool, especially if you're not deep enough to get under the top surface and start breaking chips from under the nitrocarburization. If you're just skimming real shallow along a surface completely treated, you're just going to burn up your tool and make it worthless.
1/8" sucks, too. You need to go thicker with your first tool, imo, so you get a little better rigidity without having the toolholder so close that you can't keep air/mist pointed at it. If you NEED that smaller diameter for some features, do it after you've roughed away the hard shit. Though for all the RDS I've put on Glocks and M&Ps, I've never needed to put any really tight radius features milled into it.
What are you mounting? A specific optic, an adaptor plate, a dovetail or what?
You also should give feedrate in IPM... a % means nothing, really, because we don't know what it's a percentage -of-. What's your depth of cut? You're not trying to plunge into it, right? You're leading in from the side?