Meeko,
This is from my "RUGER TIPS", may be of some help and save you time:
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#1. MODIFYING BISLEY HAMMER FOR PLOW HANDLE OR BIRDSHEAD GRIP FRAME:
Before you trace your old hammer, make sure it fits flush with the grip frame ‘ears’. If not you'll want to leave the Bisley hammer larger than the original to final fit flush with grip frame ears.
Use the hammer pivot pin to hold the original and new hammers together and scribe both sides, then grind, file, sand and re-blue (if blued), the portion you filed away.
I "hog off" most of the metal with an 1/8" x 1" Dremel course stone; hammer in a vise, or use a cutoff wheel mounted in a bench top grinder. Then true up the course grinding by 'draw filing' with a small double cut triangular file and then square up the corner. Finish with 400 grit paper wrapped around a 1/4" x 1/2" alum sanding block with flat surfaces, and re-blue with Brownells OxPho blue. That will match the factory finish which is left a bit course. For a higher polish, follow up with 800 grit and 1000 grit. Polish with a Dremel flannel wheel using white rouge made for polishing stainless steel. Then blue.
Stock Bisley hammer in rear, modified Bisley center and standard hammer in front (G2’s photo):
#2. 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, trigger OR 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. 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. Install in reverse! Piece o’ cake.
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. Almost always there will be a huge flat 'roll-over’ burr in each hole from the milling cuts that expose the holes (the New Vaquero and New FT BH guns no longer have these projections and milling cuts). 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 Model Rugers, the first thing to check is the transfer bar clearance with hammer for reliable firing pin function.
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 step of the hammer nose so the transfer bar is pushed tight against the firing pin and hammer channel. 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, 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, and 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 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 so the hammer falls. The round will not fire if safety transfer bar is functioning correctly.
#4. BISLEY TRIGGER INSTALLATION FOR PLOW HANDLE OR BIRDSHEAD GRIP FRAME:
The slot in the grip frame must be extended 5/16” and the 45 degree angle at the front of the slot replicated to install the Bisley trigger in a plow handle or birdshead GF. The best way to do this is with a cutoff wheel in a Dremel tool. Another option is to shorten the front end of the Bisley hammer to fit the existing slot.
The shorter the slot or less you take off the front top of the trigger, the further back the trigger will sit when at rest. As long as the trigger returns far enough forward to clear the hammer full cock notch. The contact of the trigger with the front of the slot dictates how far forward it will be when at rest. I now position them farther to the rear than shown on my Super Single Six above for my fat trigger finger. Although when cocked the trigger repositions far to the rear. The curved Bisley trigger is a vast improvement for my trigger control and feels like my rifles.