That's an easy swap, but here's some relative info from my tutorial:
#1. NM HAMMER CHANGES and BASE SIZES:
Hammer changes are a drop in for any New Model, but pre 2005 designed hammers have a cosmetic issue on any gun or grip frame newer than 1998. And it's always an issue on the NVs and new Flat Tops, because they are the only models whose hammers have the newer large base.
The SBH and standard hammers in the regular Blackhawks, original Vaqueros, and Single sixes don't fit well in newer than 1998 guns and grip frames because their hammers are all of the old design with bases that are the small size. And if you file the grip frame ears to fit a pre 1998 main frame, the new hammer and the original hammer will both look better.
If I have to 'dress' down the grip frame ears to match cyl frame I always dress them flush with the hammer base.
If you have a blue gun you have to do some cold blue touchup though. And Ruger is not making any more blue hammers or triggers, all the new blue guns come with stainless Hs & Ts.
To simplify production in about 1997, Ruger increased the height of the standard cylinder frame mating surfaces on both sides of the hammer ~1/16” to match the Bisley model frame ears so any style grip frame could be assembled to any main frame. Therefore the ears on all other standard grip frames after 1997 had to be made ~ 1/16” taller as well. But Ruger has only enlarged the hammer base to match the taller grip frame ears on the newly designed hammers introduced since 2005 such as the New Vaq standard ‘long horn’ and Montado hammers, and the NM Flat Top Blackhawk hammers, and the .327 Single Seven hammers.
All other hammers designed prior to 2005 used on current model guns are small base and do not match the post 1997 tall eared grip frames. Some people don’t mind. If I install a small base hammer in a post 1997 gun, I fit the grip frame ears to the hammer. I also have to do this every time I install post 1997 grip frame such as the N Vaq and Flat Top XR3 size steel grip frames or XRE-RED size steel grip frames on pre 1997 New Models or on Old Model Rugers.
The result is that the SBH hammer base doesn't fill the slot in a post 1998 grip frame.
Mike Campbell photo.
Right hand hammer is after c. 2005 up to current production with large base 1.122” – 1.130” (Flat Top and New Vaquero only).
Mike Campbell photo.
The top small base hammer 1.071” – 1.076” predates the c. 2005 large base new hammer designs. Measured on the centerline of the two large holes from back of hammer base to over the full cock notch.
The hammer underneath is a new Flat Top Blackhawk with large base 1.122” – 1.130” and narrow shank.
Mike Campbell photo.
Ruger's change to narrower shank hammers (except Montado hammers) coincides with the larger base hammers that fit the grip frame ears we only see on those newly designed hammers for the New Vaqs and the 1st anniversary new mid-size flat tops introduced in 2005. And the 2006 and later mid frame and large frame flat tops which in my opinion are much better looking. I know of no other reason for it other than the improved looks. For many years I was relieving the shanks by hand.
http://www.rugerforum.com/phpBB3/viewtopic.php?f=3&t=213730&p=2136804#p2136804
NOTE: I usually take about 1/16" off the back of the old design hammer shank below the spur because they stick out from the frame recoil shield too far for my taste, but don't go too far or the hammer plunger/spring hole will be exposed.
Hammers with a U notch in the upper hammer face appeared on some hammers when Ruger began to make new model mid-frames as near as I can tell. Hammers with the notch will function properly in the two different frame sizes.
But if the upper front extension of the replacement hammer face is longer than necessary, it will not clear the firing pin when the trigger is not being pulled and the transfer bar is in the lowered position. You will see the firing pin protrude into the cyl window. If that's the case, the extension on the hammer should be relieved at the lower edge. It can be filed straight across, the u shape is not needed.
#2. MY SHORTCUT FOR REMOVING JUST HAMMER and/or PAWL:
Recognize, you do not need to hassle with the PESKY LOADING GATE SPRING, pull the trigger pin, OR trigger/transfer bar JUST to remove the hammer and pawl. Once you remove the grip frame, the hammer pin is the only other part you need to remove. After that, just pull the hammer back and all the way down, then depress the hammer plunger in the base of the hammer with a small tipped screwdriver to clear the trigger extension where the transfer bar connects to it. Let the hammer & pawl fall out. Reinstall the hammer and pawl back in the same way they came out. Push the plunger in by pushing it against the trigger extension just like you did with the tip of the small screwdriver, and the hammer will slip by the trigger extension. Piece o’ cake.
Occasionally a hammer change that just barely cocks is because it's hitting the back of the slot in the grip frame. I have had to slightly lengthen the slot with a few file strokes.
If either the trigger or hammer pin are snug fits, after they’re removed the first time, it’s the opportunity to polish them so they’re slip fits to put back in and remove the next time.
TIPS FOR INSTALLING GRIP FRAMES:
Install all five screws but do not cinch them tight. Align the grip frame edges flush with the cyl frame by tapping with the butt of a plastic handled screw driver. Tighten one trigger guard screw, then front screw and then one ear screw. Then tighten them all. Check for ease of hammer movement to be sure it's not rubbing on grip frame ears.
NOTE: While you have the grip frame off, it's always good to examine the upper end of all the grip frame blind screw holes for thread shavings that weren't cleaned out from the factory and get crammed in there by the screws.
Also check the two trigger guard screw holes where they are exposed by the milling cut if your grip frame has the two projections that go into the main frame (the New Vaquero and New FT BH guns no longer have these projections and milling cuts). Almost always there will be a huge flat 'roll-over’ burr in each hole from the milling cuts that expose the holes. If they are present they generally cause the 1st 1/8" of removing those two screws to take extra effort to unscrew. You'll need to break off the burrs and pick them out with a dental pick or equivalent tool.
#3. AFTER CHANGING HAMMERS IN NEW MODELS:
The first thing to check is the transfer bar clearance with hammer for reliable firing pin function. When swapping hammers between two guns, it often helps To swap transfer bars as well for proper ignition and to insure the safety feature still works correctly.
TO TEST HAMMER/TRANSFER BAR FOR MISS-FIRES:
With hammer fully cocked, press on the transfer bar to extend the firing pin and observe how far thru the recoil shield it protrudes. Now keep the trigger pulled back, drop the hammer and observe the firing pin again. If firing pin protrudes the same amount, you’re good to go. If it doesn't protrude the same amount, you need to remove just enough metal from the top face of the hammer nose so the transfer bar is pushed tight against the firing pin and the frame. If you remove too much, the transfer bar will not perform its safety function and will be pinched. Also make sure hammer has no friction or contact with grip frame ears around its base to slow its fall and you may have miss-fires; another potential issue when making hammer changes.
IF TRIGGER DOESN”T RETURN, TRANSFER BAR IS PINCHED AND SAFETY IS NOT WORKING:
If the transfer bar is hanging up under the hammer face, since it's connected to the trigger, it prevents the trigger from returning. The transfer bar is slightly too thick. If both ends of the trigger return spring are connected (under the grips), or even if you have only one leg of the spring connected it should pull down the transfer bar if it's the correct thickness. When this happens, the transfer bar safety function will not work. If the gun were dropped, a live round in the chamber under the hammer will fire.
This is not uncommon however, and it's a very simple fix. File the second step of the hammer face, counting from the top, just a bit until the bar no longer hangs up. Don't take too much off or you'll have miss-fires. If that happens file a little more off the top step of the hammer.
IF YOU HAD TO MODIFY HAMMER NOSE:
At the range, double check the safety function by loading a live round in the next chamber to cycle under the hammer, point down range, cock the hammer, hold with thumb, release the trigger to uncock the hammer, take finger off trigger and release your thumb to let the hammer fall. The round will not fire if safety transfer bar is functioning correctly.
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