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Installing a Half-Cock Hammer in an Old Model Ruger® Vaquero®
by Roy Seifert

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Disclaimer:  This article is for entertainment only and is not to be used in lieu of a qualified gunsmith.  Please defer all firearms work to a qualified gunsmith.  Any loads mentioned in this article are my loads for my guns and have been carefully worked up using established guidelines and special tools.  The author assumes no responsibility or liability for use of these loads, or use or misuse of this article.  Please note that I am not a professional gunsmith, just a shooting enthusiast and hobbyist, as well as a tinkerer.  This article explains work that I performed to my guns without the assistance of a qualified gunsmith.  Some procedures described in this article require special tools and cannot/should not be performed without them.

Warning:  Disassembling and tinkering with your firearm may void the warranty.  I claim no responsibility for use or misuse of this article.  Again, this article is for entertainment purposes only!

Tools and firearms are the trademark/service mark or registered trademark of their respective manufacturers.

It’s probably been over seven years since I’ve participated in a Cowboy Action Shooting™ match.  Being laid-off from work and gaining enough weight that my outfits and leather no longer fit certainly had something to do with it.  I also lost my long-time shooting partners; one moved 100 miles away, another one only shoots IPSC now, and the third had some serious financial setbacks that caused him to have to sell all of his guns!

Well, I’ve been gainfully employed for over five years now, I’m starting to lose weight, and my friend who moved away, Lone Star, is now retired and wants to start cowboy shooting again.  (If only the price of gas would come down!)  So it’s time to dust off the ol’ shootin’ irons and get back into the game.

I have two stainless steel old-model, large-frame Ruger Vaqueros in .45 Long Colt with 5 1/2“ barrels that I decided to modify as follows to make them more cowboy match friendly:

  • Install a free-spin pawl – this allows the cylinder to rotate freely forward or backward which makes loading and reloading quick and easy.
  • Install a half-cock hammer – this allows the chambers in the cylinder to align properly with the loading gate, allows recovery from the dreaded skipped round if the hammer misses the full cock position, and gives the cool extra click when cocking the hammer similar to a Colt single-action revolver.

These “improvements” required installing one new part, the half-cock hammer, and modifying three factory parts, pawl, trigger, and transfer bar, in order to function correctly

The Dreaded Skipped Round
The dreaded skipped round is caused by the following sequence of events:

  1. The shooter cocks the hammer with the off hand.
  2. When the gun fires recoil causes the “plow-share” grip to rotate in the shooting hand.  The heavier the load, the more pronounced is the rotation.
  3. Eventually the gun rotates enough so the web of the shooting hand prevents the hammer from locking back into the fully cocked position.  However, the cylinder has already rotated so the next live round is in firing position.
  4. The cocking thumb releases the hammer, but because it did not lock back into the fully cocked position it moves forward with not quite enough force to fire the round.  Because the hammer falls completely forward it resets the action.
  5. The shooter repositions the shooting hand so the hammer can be fully cocked.  Because the action was reset by the slipped hammer, cocking the hammer rotates the live round that did not get fired out of position and the next live round moves into firing position.  The shooter just skipped a round.
  6. The shooter now has to cycle the action five times to find and fire the missed round causing a delay “on the clock”.

I eliminated this problem by training myself to hold the gun with my little finger hanging below the grip.  This prevented the gun from rotating in my hand under recoil and avoided the skipped round problem.  Installing a hammer with a half-cock notch would not eliminate this problem, but it would prevent skipping a round because if the hammer slipped it would fall on the half-cock notch instead of completely forward so the action would not be reset.  If I cocked the hammer again it would not bypass the live round.  By the way, this only works if I don’t keep the trigger pressed, which I don’t.

Speaking with the Grand Master Himself
When the new hammers arrived I found they were incorrectly packaged with instructions for a Ruger 10/22 trigger guard so I called Power Custom Inc. to see if I could get the correct instructions faxed or emailed out to me.  I called on a Saturday and lo and behold, I spoke with Ron Power himself.  I already knew what had to be done for modifications, but Ron gave me some additional tips:

  1. Be sure to mill the top of the trigger sear engagement surface, not the bottom.  Also be sure the trigger fits into the half-cock notch or it will break off the front of the notch.
  2. Lengthen the notch in the transfer bar by 0.090 – 0.100”, I chose the middle of 0.095”.  He said to use a file, but that a carbide mill would work.
  3. Once the gun is reassembled make sure I can fully cock the gun for all six chambers using a gentle pull of the hammer.  If not, I would need to shorten the bottom tooth of the pawl until I could perform this.  His suggestion for filing this tooth was to remove the cylinder, cock the gun so the pawl is protruding into the frame, then place a punch behind the pawl to hold it in place.
  4. His last suggestion was to ensure the hammer plunger slipped off of the cylinder latch with the hammer about 1/8“ away from the frame.  Adjust this by filing the rear of the cylinder latch.

Complete Disassembly and Cleaning
Before beginning this project I made sure my revolvers were unloaded and completely disassembled each gun.  Refer to my article Ruger® Single-Action Revolver Disassembly/Reassembly and Spring Replacement.  I did one revolver at a time so I wouldn’t get the parts mixed up.  I used Q-tips and cleaning solvent to get soot out of all the nooks and crannies inside the frame.  You’d be amazed how much soot gets into the internals of the revolver!  I shoot light loads which don’t allow the brass cartridge case to expand to completely seal the chamber which causes some blowback of burning gasses.  When I decided not to shoot cowboy matches for awhile I disassembled and thoroughly cleaned each revolver before putting it away, so my revolvers were already clean, but it doesn’t hurt to go over everything again.

Making a Free Spin Pawl


The pawl is the small arm that is connected to the hammer and has two teeth; one at the top and one in the middle.  The pawl is held against the cylinder ratchet by the pawl spring and plunger.  When the loading gate is open the top tooth of the pawl allows the cylinder to rotate in only one direction.  When the cylinder is rotated clockwise the top tooth slips over each tooth of the cylinder ratchet giving the audible click. 

If the cylinder is rotated counter-clockwise a tooth of the cylinder ratchet presses against the top tooth of the pawl and prevents the cylinder from rotating backwards any farther.  Unfortunately, with the old-model Vaquero, when the cylinder is stopped against the pawl a chamber is not properly aligned with the loading gate for loading and unloading as you can see in the above figure.

As the hammer is pulled to the rear the cylinder latch (other manufacturers call this the bolt) drops down into the frame thereby unlocking the cylinder and allowing it to rotate.  The cylinder latch is the flat, half-round piece of metal that protrudes from the inside bottom of the frame.  It mates with a notch cut into the cylinder and prevents the cylinder from rotating when the gun is fired.  The top tooth of the pawl engages a tooth on the cylinder ratchet and causes the cylinder to start to rotate.  When the cylinder begins to rotate the cylinder latch moves back into the raised position and drags against the cylinder causing what some consider to be the unsightly “drag ring” on the cylinder.  As the cylinder rotates the bottom tooth of the pawl engages the next tooth on the ratchet and allows the cylinder to continue rotation until the cylinder latch locks the cylinder in place.  The teeth on the pawl control the timing of the cylinder and are fitted at the factory.

Before modifying the factory pawls on my two Vaqueros I wanted to test to make sure the half-cock hammer would function with the modified pawl.  I have a Ruger Bisley Blackhawk® that has my modified free-spin pawl.  With the loading gate closed (you can’t cock the hammer if the loading gate is open) I pulled the hammer back just enough so the cylinder latch dropped down into the frame thereby unlocking the cylinder.  With the hammer partially pulled back and the cylinder latch in the down position I was able to rotate the cylinder in only one direction as indicated by the audible clicks of the hand slipping over the ratchet.  When I rotated the cylinder backwards against the pawl I noticed that a chamber was properly aligned with the loading gate as it would be if the half-cock hammer was installed.  Ok, because this functioned properly I can modify my factory pawls.

After further analysis I determined that the modified pawl had to function correctly or the gun wouldn’t cycle!  The modified pawl does not contact the cylinder ratchet when the hammer is down, but it still has to contact the ratchet to start the cylinder rotating during the cocking cycle; refer to the above figure.

I marked the top of the pawl with a blue marker and with the hammer down and loading gate open, rotated the cylinder counter-clockwise a few times until it was stopped by the pawl.  This left a mark on the top of the pawl which told me how much metal to remove. 

By filing the top tooth at an angle it no longer contacted the cylinder ratchet and allowed the cylinder to rotate freely in either direction.  I made sure I removed just enough metal so the cylinder ratchet no longer made contact with the pawl.  If I removed too much metal the cylinder may not rotate, and/or may not contact the ratchet with the new hammer in the half-cock position.  Because I left about 1/16” it still functioned correctly when the hammer was cocked.  Refer to my article Making a Free Spin Pawl for a Ruger® Single-Action Revolver.  I have successfully performed this modification to a number of Ruger single-action revolvers. 

Once I installed the half-cock hammer, with the hammer in the half-cock position, the free spin pawl was raised just enough so that if I moved the cylinder backwards, it caught on the top tooth of the pawl with a chamber properly aligned with the loading gate as seen in the above figure. 

Modifying the Trigger
Power Custom sells the entire drop-in half-cock hammer kit that includes the half-cock hammer, modified trigger, and Wolff spring kit.  This kit is available from MidwayUSA as product # 345935.  Both of my Vaqueros already had a Wolff spring kit installed, and I knew I could successfully modify the trigger myself with my mill, so I decided just to purchase the half-cock hammer from MidwayUSA product # 439111.  MidwayUSA doesn’t stock this part so they special-ordered it for me.  This not only saved me some money, but gave me some additional gunsmithing work to perform.

The factory trigger comes with a very large sear engagement surface; too large to fit into the half-cock notch of the new hammer.  The half-cock notch measured a little over 0.050” so I would need to leave that much or a little less.  I not only needed to remove the top of the engagement surface, but I also needed to grind a little metal off of the bottom to allow the trigger to fit around the curve of the new hammer and seat into the half-cock notch as shown in the above figure.

I placed the trigger in my milling vise at the proper angle and used a 1/4” square end bit to remove the metal.  I could have used a file to remove the metal, but the milling machine insured my work was flat and square.  Then I took a small grinding stone and my high-speed rotary tool and ground a slight radius on the bottom; just enough so the trigger would fit into the half-cock notch.

The Power Custom Series 1 Stoning Fixture that I purchased from MidwayUSA product # 743549 has two holes in the top where I can set the hammer and trigger pins and see the relationship of the hammer to the trigger.  This is how I discovered that I needed to grind a radius in the bottom of the trigger.  Notice the inset in the above figure; the trigger is blocked from seating completely into the half-cock notch by the rounded shape of the full-cock notch.  By grinding a radius in the trigger where the hammer is touching the trigger will seat fully into the half-cock notch.

After I finished milling and grinding I removed any burrs and polished the surfaces.  I then installed the RSA adaptor I purchased from MidwayUSA product #765339 into my Power Custom Series 1 Stoning Fixture and honed the sear engagement surface.  I used ceramic sticks to polish the engagement surface that I purchased from Brownells, stock #080-721-621WB, the black one for coarse polishing, and the white one for final polishing.  Ceramic stones use water as the cutting agent, not oil.  I marked the engagement surface with a blue marker to ensure I was polishing it square and flat.

Modifying the Transfer Bar

The transfer bar is a safety feature of the Ruger single-action revolvers which allows the gun to be carried safely with all six chambers loaded.  With the hammer down, the transfer bar sits down out of the way of the hammer and firing pin.  When the hammer is cocked the trigger moves to the rear lifting the transfer bar up to cover the firing pin.  When the trigger is pulled to the rear the transfer bar stays in the up position, the hammer falls striking the transfer bar which transfers the hammer’s energy to the firing pin and ignites the primer of the loaded cartridge. 

The transfer bar has a notch cut into it.  When the loading gate is open the half-round protrusion at the end of the pivot pin rotates into that notch and blocks the transfer bar which prevents the hammer from being cocked.  This defeats the purpose of the half-cock hammer!  I followed Ron Power's instructions to modify the transfer bar to increase the length of the notch.  Now the hammer would not be blocked and could be placed in the half-cock position with the loading gate open.

Following Ron’s suggestions I marked the factory transfer bar with a blue marker, set my calipers to 0.095” as shown in the above figure, then scored the transfer bar to show where I needed to mill.

I put the transfer bar into my milling vise and used a 3/32” ball-end bit to remove the metal.  The ball-end bit left a radiused corner at the base of the cut which should prevent cracking.  A square-end bit would leave a sharp corner which could crack over time.

Installing the Half-Cock Hammer

Installing the new half-cock hammer was a simple matter of replacing the factory hammer, and reassembling the gun.  I made sure everything was properly lubricated before reassembly. 

First I tested the free-spin pawl by opening the loading gate and spinning the cylinder in both directions.  Then I closed the loading gate and fully cocked the hammer.  The extra click I heard as the trigger passed over the half-cock notch did sound pretty cool!  I measured trigger pull at 2 1/2 pounds, and let off was crisp and clean with no creep or drag.

All 6 chambers locked up, but the hammer was a bit tight.  I wanted just a little bit of play, so again following Ron’s directions, I removed a few thousandths from the bottom tooth until there was just a small amount of forward and backward play in the hammer when fully cocked.

Next I pulled the hammer back into the half-cock position and opened the loading gate.  I rotated the cylinder forward (clockwise) and heard the familiar clicks as the cylinder ratchet moved over the top tooth of the pawl.  I moved the cylinder backwards (counter-clockwise) until it stopped and sure enough a chamber was aligned with the loading notch in the frame.

Finally, I wanted to simulate the dreaded skipped round.  With my shooting hand held high on the grip and my finger off the trigger I pulled the hammer back until it hit the web of my hand and wouldn’t go any farther.  I let the hammer slip off my thumb and the half-cock notch caught it, but since the hammer didn’t completely fall, the action didn’t reset.  I was able to re-cock the hammer and the cylinder did not rotate so I didn’t bypass the chamber.  Even though I grip the gun with my little finger below the grip, it’s nice to have this feature as a backup.

While I had both revolvers apart I slugged the barrel and measured the chamber throats in the cylinders.  Both revolvers suffered from the typical Ruger big-bore problems:

  • The barrels slugged 0.451” but each had a constriction under the barrel threads
  • The chamber throats measured 0.4495” – 0.450”

Essentially I would have had a 0.452” bullet swaged down to 0.450” or less depending on the amount of barrel constriction, wobbling down a 0.451” barrel; not exactly a great recipe for accuracy!  I opened up the chamber throats to 0.452” and removed the constriction by hand-lapping the barrel.  Refer to my article Accurizing the Ruger® Single-Action Revolver.

So now the question is; which method do I use to load and unload the revolver?  I put the hammer in the half-cock position for normal loading and unloading.  I do the Colt loading sequence of load one chamber, skip one chamber, and then load the other four.  After loading the fifth round I close the loading gate, pull the hammer all the way back, then carefully drop the hammer over the empty chamber.

When loading under the clock I open the loading gate allowing the cylinder to free spin, load one round, rotate the cylinder counter-clockwise 2 chamber positions, then close the loading gate.  When I cock the hammer the loaded round moves into the firing position.

So why didn’t I just mill a half-cock notch into the existing hammer?  There is not enough metal on the front of the factory hammer to mill out the notch.  I would either have had to add metal to the front of the hammer and then mill the notch, or purchase a new hammer which was the better solution for me.

A special thanks to Ron Power for his suggestions to ensure my installation of his half-cock hammers went smoothly.  Thanks to him both of my Vaqueros are ready for competition.


   © Copyright 2012 Roy Seifert.