And this is the custom part you need to make to hold the trigger plunger spring in place on your new model grip frame.
View attachment 146680
It‘s not much, I’ve seen them made from a spent .22 casing.
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you’ll need one of the adapter methods below:
You can make the simple aluminum adapter shown below to fit in the NM GF behind the old model trigger or just use a .22 LR case to hold the return spring and plunger in place.
Either will need the one NM trigger return spring retaining pin closest to the trigger shown below to hold your OM trigger return spring/plunger adapter or .22 case in place. File a small notch in the .22 case head to nest on the retaining pin.
3] Or you can use an old model trigger with a shelf soldered on the back for the NM trigger return spring and GF like the Clements adapter trigger shown above.
4] The very easiest swap is a Ruger Old Army steel or SS old model style grip frame already designed for the old model plunger and return spring. They also have a wide trigger slot. The Clements adapter trigger with the shelf for NM return spring ground off is easier and cheaper than finding an OM wide trigger.”