Remove the SA notch on a SP101 hammer

[ammo dave]

I have a SP101 that I would like to convert to DAO only. I found a hammer and removed the spur and now I would like to remove the SA notch on the hammer.
There is a tiny notch on the front toe of the hammer (arrow on my pic below). Do I just stone that off to eliminate the SA mode? I asked this question on the Ruger forum but got no useful responses. Hammers are hard to come by, can anyone help?SP101 hammer.jpg

[44 AMP]

I understand the arguments pro and con for bobbing/dehorning the hammer, I've never understood the reasoning behind converting a DA revolver into DAO.

If you don't like the SA feature, simply don't use it.

Do be aware that if your gun goes back to Ruger for ANY reason, they will remove your customized parts (and probably throw them away) and return the gun to factory original configuration before returning it. That has been their policy for some time now.

[ammo dave]

It's possible to engage the SA notch on a spurless hammer but difficult to safely decock the hammer without a spur. I want to remove the SA notch. Anyone know how to do that?

[tangolima]

The hammer looks already bobbed. One would need tool to cock it for SA. I wouldn't bother. You op insisted, I have more than one way to knock it out.

-TL

Sent from my SM-N960U using Tapatalk

[tangolima]

Originally Posted by ammo dave

It's possible to engage the SA notch on a spurless hammer but difficult to safely decock the hammer without a spur. I want to remove the SA notch. Anyone know how to do that?

Putting a finger or bottom of your palm between the cocked hammer and frame.

-TL

Sent from my SM-N960U using Tapatalk

[ammo dave]

tangolima please share your method(s) for removing the SA notch.

[tangolima]

Originally Posted by ammo dave

tangolima please share your method(s) for removing the SA notch.

Please PM me.

-TL

Sent from my SM-N960U using Tapatalk

[ammo dave]

I've asked this question on several forums but apparently no one know how to do this.

[Jim Watson]

That is the full cock notch. I think that if you file it off, the SA will be gone.
But a slip of the hand, you might get into the toe of the hammer and impair the DA.
I saw a Smith that an Expert Genius had mucked up attempting a DAO conversion.
As tango says, if you don't cock it, you don't have to decock it.

[tangolima]

Originally Posted by ammo dave

I've asked this question on several forums but apparently no one know how to do this.

PM replied.

One more time and I will keep my mouth shut; I wouldn't do it if I were you.

-TL

Sent from my SM-N960U using Tapatalk

[WmMunny]

Just 2ondering-- if you cut off the hammer spur, does the hammer's reduced weight/mass reduce the force and therefore the reliability of the primer strike?

[Jim Watson]

I know a guy who bobbed a Taurus hammer and got misfires. He crammed in a S&W spring and got it going.

[Don P]

Just 2ondering-- if you cut off the hammer spur, does the hammer's reduced weight/mass reduce the force and therefore the reliability of the primer strike?

No, when I removed the spur on my GP-100 it weighed about 6 grains which had no effect on primer strikes. The force of the hammer strike comes from the hammer spring

[Dfariswheel]

There's a school of thought that a lighter hammer gives faster strike and increased ignition.

In any case, converting most revolvers in general and the Ruger SP-101 in particular to DAO is not rocket science, and it ain't risking Armageddon.
Just grind away the single action ledge on the hammer and done.

[Unclenick]

Ignition is dependent on the energy with which the firing pin strike occurs. The military measures it by dropping a weight onto a firing pin already in contact with a primed case that points down. The weight in pounds times the distance fallen is the work and energy value (both in lb-in, in that instance). For a firearm, they have steel anvils that look like a chamber headspace gauge except for a blind hole where the primer pocket in a cartridge case would be. A calibrated copper pellet is placed in the blind hole, and the depth of the firing pin indentation they get on it is used to indicate the energy of the firing pin strike.

In the case of your revolver, there is kinetic energy in the hammer mass, the equivalent of half the spring's mass, plus the potential energy in the tension on the spring, and all three add up to affect the impact energy of the firing pin.

Whether lowering hammer mass improves or degrades the total energy depends on the spring's strength and mass, as well as the hammer's. Either can happen, depending on the combination. The key is how much speed is added to the hammer by lightening it. Kinetic energy goes up as the square of velocity, so if you cut the hammer mass in half and its speed increases by a factor of 1.414 (the square root of 2), you have no net difference in the hammer's energy. However, the spring has to accelerate its own mass as well as the hammer's, and if that is great enough in comparison to the hammer's mass, it may not be able to get the hammer to speed up that much. Additionally, the transfer of energy from the spring to the firing pin is an event in which there is initial energy transfer followed by the momentum in the spring's mass compressing it forward a little before it bounces back to settle in the fired state. The portion of its energy transfer that is delayed in delivery that way cannot be counted on to make a reliable contribution to getting the primer lit up.

So, it's messy.


Ammo Dave,

If you file off the small full-cock hammer hook, as shown on the right below, the sear nose will no longer have any place to catch. I am not recommending you do this. YOU MAKE ALTERATIONS AT YOUR OWN RISK, INCLUDING THAT THIS OR OTHER ALTERATIONS MAY CAUSE ISSUES THAT REQUIRE FACTORY SERVICE TO REPAIR AND MAKE SAFE. NEITHER THE BOARD NOR THE POSTER WILL ASSUME ANY RESPONSIBILITY FOR THE OUTCOME OF THIS ALTERATION. In this instance, I am having a bit of trouble envisioning why this is safer than leaving it alone. When decocking an exposed hammer, I put my weak hand thumb between the hammer and the frame to catch a slip, and ease it out of the way after the hammer is far enough forward not to be likely to be able to get up enough speed to have the energy to fire a round (gun still pointed in a safe direction, of course). But it's your gun

[mehavey]

As briefly mentioned above -- once you've removed the spur as shown in the OP's Post #1,
how would you be able to pull/get the gun into SA condition (i.e. "cocked") ever again?

And if double action were then the only operation possible, how would any single-action
notch ever come into play again -- even it it still existed?

At that point, why do anything else to the hammer?
(just curious)

[Jim Watson]

once you've removed the spur as shown in the OP's Post #1,
how would you be able to pull/get the gun into SA condition (i.e. "cocked") ever again?

You start the hammer back by pulling the trigger part way, then kind of hook your thumb over the top of the hammer and pull it on back to full cock.

Now when John Henry Fitzgerald was mutilating Colts by cutting out the triggerguard and cutting off the hammer spur, he checkered the top of the hammer to allow cocking.

[mehavey]

start the hammer back by pulling the trigger part way, then kind of hook
your thumb over the top of the hammer and pull it on back to full cock.

Why (after going to the trouble of cutting the hammer spur off
for default double action) would anyone ever do that?

(he asks.... )

[4V50 Gary]

It's easy enouugh to file down the SA notch on a hammer. LAPD used to do this to all their revolvers and my brother bought a duty revolver from a widow whose husband retired from there. I bought a new hammer and restored the SA feature.

I wouldn't do file down the SA notch though. If you want DA, just use the DA and train with it. We were never allowed to SA our revovers in training and I'm grateful for have trained on DA.