MIM
No one has addressed this in this thread so I will. They are not really cast parts. MIM stands for Metallic Injection Molded. The powdered metal is mixed with a polymer to create a "slurry" that is then injection molded at fairly low temperatures. The part comes out of the mold 20% oversize. They are then heat treated, and this high heat removes the polymer and reduces the size of the part to what it is supposed to be. The result is extremely consistant parts; one to the other. Much more so than the forged parts. This allows the guns to be assembled with much less labor and less handwork and makes them more consistant gun to gun. along with the computer machining of the frames, this allows more consistant distances between the frame pins that hold the parts in the action of the revolver, and along with the more consistant hammers and triggers, they come closer to dropping in with little or no fitting.
The above is per S&W.
They started with MIM parts in the auto pistols, and one of the first parts was the disconnector in the 9mm series. They were originally a stamped part with a seperate cross pin pressed in. Then they went to an all plastic disconnector. neither of these were really satisfactory, and the MIM part solved the problems. Another early MIM part in the auto pistols was the trigger bar. The original forged ones were the ones that used to break. They went to MIM on the draw bars and were able to put radiused corners on the inside where the draw bar goes around the magazine, (the sharp corners was where they used to break) and this fixed the draw bar breaking. Most people did not even know they had MIM parts in their guns, and it did not really come to light until they did the revolver hammers and triggers and since they were so obvious, it was out.
The MIM process allows such precision, that S&W tried doing a J frame 38 with the barrel and frame in one piece, and they could even have it come out of the heat treat with the rifling in place! Imagine one solid piece with no screw in barrel. The problem was, with a large and long part like that, they tended to warp in the heat treat process, and as they were not able to get past that, they dropped the idea and have kept it to smaller parts.
The MIM parts are a little different than the forged parts so they could be molded. The triggers no longer require the cross pins the forged ones had to have to hold the hand spring and all of this saves labor and keeps costs down. In my opinion, the MIM parts are just as good as the forged ones. The forged parts were prettier. Also, I see no sign of case hardening on the MIM parts. They are case colored but I believe them to be equally hard all the way through.................
Louie
. Cut your MIM to bob the hammer and cut it and try the punch test, same on any part.
