I know this topic has been hashed over before, but it seems like most have just muddied the waters. For the sake of simplicity we will limit this discussion to the Single Six, Blackhawk and Vaquero guns, eliminating for the most part the Super Blackhawk/Dragoon, Bisley and birds head grip frames.
So let's start at the beginning:
The Single Six was introduced in 1953. The grip frame was made to mimic that of the original Colt's. They were made of aluminum and were given the part # XR3.
The Blackhawk was introduced two years later and had the same XR3 aluminum grip frame.
Fast forward to 1963, Ruger redesigned the grip angle of the Blackhawk and Single Six, the frames were still made from aluminum, but now carried the part # XR3-RED (RED for redesigned).
The Ruger Old Army Black Powder revolvers used the same XR3-RED grip frame.
Fast forward another 10 years, in 1973 Ruger redesigned the trigger mechanism on all their Single Action guns (save for the Bearcat). The new design was called the "New Model" and included a transfer bar safety system. The redesign also added different springs and pins to the grip frame. It is important to note that the internal trigger & hammer parts do not interchange (with a few exceptions) with the old model guns.
The redesign also included a different trigger return spring. The coil spring and plunger design were replaced with a wound leaf style spring the pivoted on a pin and had an additional pin for the spring "ears" to pry against. See the pictures below:
The New Models also included a grip frame mounted spring & plunger for the cylinder lock (also notice the area behind the trigger is now open).
The grip angle and grip panels between the XR3-RED old model and the new model are the same but the part # changed to XR3N-RED, eventually it was shortened to XR3N. The "N" is for New model.
As far as I know there is no part number difference between the steel and aluminum grip frames. Most people prefer the steel ones, for better balance and easier refinishing, so care must be taken when ordering a new one to ensure you get the one you want.
So we have one grip frame for the New Model Blackhawks, Vaqueros and Single Sixes in Aluminum or Steel: XR3N and two grip frames for the old model: the XR3 (aluminum only) and the XR3-RED (aluminum only) depending on when the gun was made. The only difference between the XR3 & XR3-RED (old model) is the grip angle, therefore the grip panels will not interchange between them.
With the introduction of the New Vaquero in 2006, the XR3 grip frame was brought back, only now in steel exclusively. (we are talking about the redesigned Vaquero, made after 2005)
The newer XR3 grip frames on the New Vaquero & 50th Anniversary Blackhawk are the same dimensions as the old model Blackhawks & Single Sixes XR3, but they feature the trigger return pins and springs of the new model. In addition the grip panel locator pins are not in the same place as the ones on the old XR3 frames. So while they have the same profile as the original pre-1963 grip frames, the grip panels will not interchange.
What's more, some new grip frames (both XR3N & XR3) have received the new trigger locks. Ruger changed the thickness of the grip frames on some of the guns. If you have one of these guns you will need to do some research if you are planning a swap or installing aftermarket grip panels. The main spring was also shortened by two coils. So keep that in mind if you are looking for aftermarket springs.
One last thing regarding the New Vaqueros, they came with the free spin pawl (allowing the cylinder to spin both directions). The grip frames have a relief cut in the trigger guard area (see below) any older grip frame being put on one of these guns will need the same material removed.
Here is a breakdown of the models and years
Old Model 1953 - 1962 = XR3 in Aluminum only
Old Model 1963 - 1972 = XR3-RED in Aluminum only
New Model 1973 - current = XR3N-RED (or XR3N) in Steel & Aluminum (now painted instead of anodized)
Original Vaquero 1993- 2005 = XR3N in Steel only
New Vaquero & 50th Anniversary Blackhawk, 2006 - current = XR3 (with grip locator pins in a different location) in Steel.
and a different matrix, this one provided by "Hondo44" on the Ruger Forum (www.rugerforum.com)
Blue steel GFs:
All New Model Blackhawk flat top and New Vaqueros (XR3 size).
All Super Blackhawks: XR3-RED size on short barrels (the 7.5" & 10" barrels still have the dragoon style.)
All original full-size Vaqueros & .32 Mag Vaq. style Single Sixs had the XR3-RED size
Old Army beginning 1985.
Aluminum alloy grip frames:
All blue single sixes (22 and 32) except the 32 Mag Vaq style and Bisley 22s & 32s.
All full size New Model Blackhawks (not the mid-size 50th NM Blackhawk flat tops or the Bisley Blackhawks.)
All Old Models Blackhawks (pre 1973) except Super BH.
Old Army pre-1985.
So the big question: Can you use an old model grip frame on a new model gun and vice versa?
Answer: The short answer is yes:
To use an old model grip frame on a new model gun you will need to remove material behind the trigger and add provisions for the trigger return spring. You may be able to file or grind the boss off of the new model trigger so it will work with the old model return spring, but I have never seen this done, so I don't know if it will work.
You will also need to add the spring and plunger for the cylinder lock (see picture below).
Here are two cutaway illustrations from the Ruger New Model Blackhawk manual that shows the parts and how they fit togther:
This conversion rarely happens as old model grip frames were all aluminum (and scarce) and the New Model aluminum & steel frames are available new from Ruger and other retailers as well as the used market.
Here is a modification done to an old Colt frame to make provisions for a new model style trigger return spring:
A more popular swap is to use a new model grip frame on an old model gun. To do so you simply need to add provisions for the coil type trigger return spring.
Remember the old model used a coil spring and plunger for the trigger return.
This is an example of a block built from aluminum to house the old model spring and plunger, fitted in a New Model style grip frame. Notice the red circles showing the New Model trigger spring provisions. The front hole will be used to anchor the block for the old model coil spring
There is another alternative, pick up one of these custom triggers from Clements Custom Guns. It is an old model trigger, with an added boss to work with the new model return spring. The Clement's trigger is on the left, stock old model trigger is on the right
The last thing to cover is the grip frame screws. I discovered this tidbit while working on my old model Blackhawk project (look for that post later this month).
Ruger left us clues in the part numbers which help us identify which screws are the same and which ones would be different.
part numbers for the Old Model screws were:
Front: R-17 (one required)
Rear: R-18 (two required)
Bottom: R-19 (two required)
The New Model part numbers are (underline added by me):
Front: XR01700 (one required)
Rear: XR01800 (two required)
Bottom: XR01900 (one required)
Bottom Pivot Lock: XR01901(one required)
Only one of the screws is different, see the picture below from my Old Model project, it came with two sets of grip screws, which is good, because I needed two of the bottom screws but I wont need any of the pivot lock screws.
I hope that clears it up.....
Ruger Forum .net
Chisel & Plane Workshop
Clements Custom Guns
Sharps40 on Firearms Talk
Hondo44 on Rugerforum.com
CLC Custom Grips