NM grip frame adaption to use on an old model:
It's a piece of cake, a fairly easy swap. I put steel Ruger NM steel grip frames on many of my OMs. (and OM grip frames on NMs). Here's a couple of OMs with NM steel grips frames:
Notice the ears on this birdshead around the hammer still need to be fitted to the main frame:
New grip frames carbon steel or stainless steel from Ruger will come in the rough, and are a lot of work to fit to your gun, then you'll have to get it blued or polish the stainless GF. Best way to get a NM GF and grips is to buy a used 'take off' either blue or stainless; post a 'Want To Buy' in this forum's classifieds, or search ebay and Gunbroker.
Power Customs does make a 2 piece (like a Colt) for about $200 and they are top quality. I have used them. There are no modifications or any other parts needed (except Colt grips) to go on an OM. But they are not ready to just screw on, they take final match fitting to your OM main frame, and they'll need to be blued, or polished if you choose the stainless version which is $30 more.
In general: All Ruger SA grip frames including SBH Dragoon, Old Army, Bisley and Birdshead (excluding Bearcats of course) will interchange from the standpoint of the screw pattern from Single Six to Super BH, Old Model to New Model, and even NM to OM.
The hammer, all the screws, mainspring/spring seat/strut, and pins can be transferred over from your OM Grip Frame.
But if you want a Bisley hammer, you'll need a Clements or Powers Custom Bisley custom OM hammer.
THE ONLY ADAPTATION NEEDED FOR A NEW MODEL GRIP FRAME TO AN OLD MODEL IS THE TRIGGER AND RETURN SPRING, AND THERE ARE 3 OPTIONS:
1. You can use the NM trigger return spring on old model guns with a Clements adapter trigger. This is the easiest way and the trigger is wide to fit the wide trigger slot in all NM grip frames. This is required if you want a Bisley trigger.
You'll also need the NM grip frame trigger return spring and both pins to use a Clements trigger.
___________________________Clements adapter triggers are the center two_________________________
OM trigger__________________standard____&____Bisley w/over travel stop__________________NM Bisley
They are $65 and are a 'drop in'. http://www.clementscustomguns.com/
2. Another option is to use your OM trigger and return spring/plunger. Or the OM Super BH/Ruger old army wide triggers to fill the wide slot in the NM GF, but hard to find and $55 or more if you do. And you'll need one of the adapter methods below:
You can make the simple aluminum adapter above 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. The very easiest swap is a Ruger Old Army steel or SS old model style grip frame already designed for the old model trigger 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.
