Originally Posted by B Jordan
Any reason why I can't make a recoil lug out of some ground tool steel for an xp I tried making one out of a Ptg lug but it was too hard and had trouble breaking the small carbide drill bits I had ..just drilling the holes was thinking about making a 1/2 " thick lug and not hardening it ....any thought on grade of steel? Do I need to get it reground if I do decide to harden it? Different Ideas ? It's going to be a 7mm wsm with a brake
here's a couple options you might be interested in.
* buy a piece of 4150 pretreat steel in a ground finish. It's prehardened steel, but also still machineable. You can get it in 1/8th" steps from as thin as .250" (it actually has about .020" extra stock on each face). The hardness spec is 28-32RC, and probably plenty good enough. This stuff is very strong steel. If you go this route, I recommend the stuff that Baldwin Steel sells (out of PA.). It just seems to machine better. Plus if you desire, you can have the recoil lug nitride hardened. I'll cover pit falls on these two steels later.
* O-1 gauge stock is the other way. Not as strong as the 4150, but machines very well. Also easy to come by. You can buy it in just about every size from 1/32" to well over an inch thick.
* every now and then you can run across 4350 pretreat steel in a ground finish. I think this might be a little better than the 4150, but the 4150 will probably be a lot easier to find, and easier yet to machine. I have seen A2 and D1 and D2 plate in a ground finish, but you'll end up paying a lot more. Not exactly the best to machine unless your setup to do it. A2 hardens very well, and changes very little if you by quality steel.
Now for the pit falls (you know there has to be some). The ground finish steel may or may not change a little on you as you machine (4150 & 4350). You'll mostly see this in the flatness, but even then it won't be more than .005". I have seen generic batches of it shrink (and some lots even grow) during nitride, but this is not all that common with the better brands. Expect the O-1 & O-6 gauge stock to move all over the place during heat treat and a draw back. Also have the parts x-rayed for cracks around the bore area. You'll have to grind this one back to being flat and the metal will shrink during heat treat.
A2 won't change size much at all. But doesn't machine as well. Heat may be a problem as it's air hardening steel (I really like this stuff). Has a tendency to work harden during machining, unless your on top of your game. D2 is even worse! There is also the "S" series, and this would make the best recoil lug in my book, but even harder to work with. If you find some S-5 or S-3 (never machined S-3), you got the good stuff. But a regular S.O.B. to work with. In a regular machine shop, they can do it without too much trouble. But for a guy at home, I'd say "no."
Now if you go the 4150 route, have it nitrided with a .025" case. This will come in extremely ridged, and be very strong. When you get it back from nitride, I'd either lap it flat, or stone it flat (won't change very much). If by chance you have access to a wire EDM, then simply drill a quarter inch hole thru the bore area. Then wire out the shape and bore (do four or five of them at once). There is no tool pressure, so the steel stays flat. This same method works well with all the others I might add, and you never have to deal with work hardening in the steel.