The internal lock was deleted in 2012.
Use a Ruger Bearcat spring seat for a Lock by-pass:
I used to make titanium lock bypass seats for sale:
One day back in 2007 I figured out that there's a $2.00 Ruger part that will work as a lock bypass! I realized that the spring seat in my Bearcat is the longest seat made for the Ruger single actions, go figure!! And it just bridges the gap in the grip frames with internal lock! That's all I use now.
The beauty of it is that a temporary pin used to hold the spring compressed when gun is disassembled, sits in the groove in the top of the Bearcat seat and the bottom end of the strut goes thru the seat just like it would in the lock. The Bearcat spring seat is the easiest swap there is. After cocking the hammer, a disassembly pin is inserted into the strut hole above the seat just like the lock, therefore the spring doesn't need to be dismounted from the strut.
In fact you don't even need to remove the grip frame! In all the other Ruger SAs, the pin is inserted below the seat and it's captured on the strut with the spring. Just place the Bearcat seat on the strut below the spring and pin, and insert together into the grip frame and onto the two shelves. Now cock the hammer, remove the spring retaining pin, and drop the hammer.
The seat doesn't overhang the gap very much on either side but it does work and I've been using these for several years on several guns.
If you want, you can file a small shelf on either side of the gap in the grip frame to insure it doesn't slip out.
File the two little shelf notches, one on each edge of the gap where the lock was, with the distance between the notches the same as the Bearcat seat length. The notches create a shelf for each end of the Bearcat seat to fit down into. That way it can't move forward or backward and fall into the gap where the lock was.
Brownells #780-000-948AK $2.12, OM Serial # Above 93-00000, and NM:
http://www.brownells.com/handgun-parts/frame-parts/mainspring-parts/mainsprings/mainspring-seat-sku780000948-11856-28534.aspx?sku=780000948
Or order direct from Ruger, part # PR5.
Bearcat seat pic in a Bearcat grip frame here: http://www.gunblast.com/images/Hamm_Ruger-SA-GripFrames/Dsc00106.jpg
Tip: use the 25 coils spring and strut that came with the lock and you don't have to dismount and remount the spring, because the temporary take down pin is inserted above the Bearcat seat like with the lock! Makes for a much better hammer pull and trigger pull, especially on the single six frames with less leverage due to the shorter hammer. Much easier for the grandkids too. Also, the shorter strut and 25 coil spring can be used with any standard grip frame that was not originally equipped with the lock, as long as you use the Bearcat spring seat. And you won't need to file the notches either.