Ruger XR, XR3-RED & New Model grip frames.
There is considerable confusion relative to the factory nomenclature used to identify the different generations of grip frames used on the Ruger single action revolvers.
The XR3 was the original grip frame casting that replicated the Colt single action size and shape. This grip frame is typically found on early flat top Blackhawk and Single Six revolvers.
The XR3-RED grip frame was the last grip frame used on the three screw Blackhawk and Single-Six models. The RED stands for redesigned and indicates that the shape and dimensions of the grip frame mold where changed from the original XR3 mold.
The XR3-RED grip frame is no longer available as a replacement part. A point of interest is that the grip frames from the Ruger Old Army, CB00300, #780-000-115 blue and KCB00300, #780-000-394 stainless steel, are effectively XR3-RED style grip frames and may be used as replacements for same.
With the redesign of the Blackhawk action in to what is now called the New Model the trigger return spring was changed. This change no longer required the return spring and plunger formally required in the XR3-RED grip frame. The New Model grip frame eliminates the hole for the trigger return spring and plunger hole that is found in the XR3-RED grip frame. The New Model grip frame (for the Blackhawk, Vaquero and Single-Six) is designated as XR00300.
Frequently the XR00300 grip frame is mistakenly referred to as the XR3-RED grip frame. This is not technically correct although the contour of the XR3-RED and XR00300 grip frames are the same and will use the same grip panels.