Half-cock On Sti Not Holding. Why?

[Jack Suber]

Got another question for y'all. Today, my son and I were trying to get one more practice session in before the A6. I make it a habit of checking his pistol (making sure safeties work, etc.) before I let him shoot it. He shoots an old STI of mine, with a Koenig hammer and EGW sear. The set-up has AT LEAST 20K rounds through it. Today, I noticed that the half-cock is not working. If the half-cock is engaged, I can squeeze the trigger (with normal tension) and the hammer will fall off of half-cock. I know this isn't supposed to happen. So, now I am trying to figure out why? For the life of me I can't see where any of the parts are worn excessively. I tried a new disconnector, trigger, but it still happens. I even tried a different hammer (used though) and it still happened. What am I missing? I have spent the last few hours trying to identify the cause and can not. I did shoot the gun and tested to see if the hammer followed and it seemed to function OK. Should I let him shoot it until I get the problem worked out? We leave for the A6 Friday morning so I need to get it squared away before then. Any ideas? Is it possible for the grip to get worn to the point to where internals don't fit the way they should? When the top end is off I can watch the trigger engage the disconnect and the hammer then falls from half-cock to fully down.

On another note - George at EGW received my broken sear (earlier post) and checked it out. He pointed out some peening on the sear face that appears to have been done by the half cock hook on the hammer - probably caused by my over-travel screw being in to far. I noticed this mark before I sent it too him. Anyway, even though the broken sear was well used, he sent me a replacement. Thats customer service. Thanks, George.

[shred]

Some hammers don't have a 'captive' half-cock notch and will do that. In theory there isn't enough energy in the half hammer-fall to set off a primer.

[Jack Suber]

Whew! It ain't as bad as I thought. George at EGW gave me a test. He told me to make sure the gun was unloaded and "and then do it again" . Then he said to knock the gun out of battery with my hand. If the sear engages the half-cock, I am OK. Well, it did. So, I was worrying for nothing. Funny thing is that when I do this test, I can't make the hammer fall off of half-cock. It will only do it when I cock it manually. Oh well. At least it is OK to shoot. Thanks for the feedback, Shred.

[Crusher]

As far as I know (and have seen) the Koenig hammer does NOT have a captive half cock notch, all can be released from the halfcock by pressing the trigger.

[lynn jones]

check the screws that hold the frame to the grip. sometimes they loosen up and will cause problems.

lynn

[Bigbadaboom]

Sometimes the hammers half-cock notch will not "capture" the sear nose completely when cocking the gun, but will when the hammer falls outside of propper sequence. Looking at the attached photo you can see the arrow pointing to the spot where the sear nose will catch during the cocking action. This is why you can pull the trigger and activate the hammer. When the hammer falls out of sequence the sear nose falls into the full notch and will not allow the hammer to fall during trigger pull. This is all due to hammer pivot direction. When cocking the hammer it is rotating up and when you feel the half-cock notch engage you stop prior to allowing the half-cock notch center nose to pass the sear nose causing the sear to hold the hammer by the outside edges that the arrow is pointing to. If you cock the hammer farther so that the sear nose will pass the notch center nose thus allowing the sear nose to fall back into the half-cock notch completely the hammer will not fall when the trigger is pulled.

I really hope that my explaination comes across well

[bountyhunter]

Sometimes the hammers half-cock notch will not "capture" the sear nose completely when cocking the gun, but will when the hammer falls outside of propper sequence.

If you look at the half cock notch on some hammers, there is intentionally a "lip" at the front edge to help capture the tip of the sear. But even with that, it may still be possible to pull the trigger hard enough to get the sear to go by it and let the hammer fall. BTW, don't do it because you are dragging the sear face across that ridged edge which is not good for it.

On some, there is no lip so the sear will pull easily by as you press the trigger.

The half cock notch is simply required to catch the hammer as it falls, either due to a person "thumbing it down" carelessly or if the hammer sets on the full cock notch and gets "jarred loose" when the slide hits the frame going into battery (which can happen if the trigger job is screwed up). The latter is called hammer follow and is quite common. Without the half cock notch, it would cause full auto fire.

Sounds like your gun is working OK.

[Josh Biondi]

Sometime in past time I got the same trouble and it happened because the sear nose was a little bit short because it was worked incorrectly and it engaged the hammer half hook too shortly. Infact if you pull the trigger with the hammer on half cock and observe it attetly you can see that the trigger go back for a little. If the sear noise that engage the hammer half hook is really short the hammer will go down. If you wanna try change the sear with a new one and the problem will be solve!

However if the sear capture the hammer when it fall down if you dont pull the trigger the sear will work correctly because its the safety job which the sear must do in the half hook.

[Crusher]

Attached is a link to (Brownells) Koenig Low Mass hammer. While not a great angle to see the diffrence in the half-cock notch between Badaboom's pic there is no "capture" hook to prevent the hammer from being released when depressing the trigger if the hammer is on the half cock notch.

As posted before there is not enough inertia when the hammer is at half-cock to ignite the round if the trigger is depressed. So no worries as long as all saftey tests are passed.

Koenig Low Mass hammer pic

[Anthony Lombardo]

Make sure you have enough pretravel, also. Usually a min of .035

I would guess your sear may be a little short also.

[Radical Precision Designs]

Make sure you have enough pretravel, also. Usually a min of .035

I would guess your sear may be a little short also.

There has been quite a bit of "reconfiguring" since dear old Mr. Browning came up with the original design.

Todays "race rigs" are like a thorough-bred horse compared to a donkey.

The geometry of a Koenig hammer is unlike many others in the positioning and "camming" design of both the full and half cock. Additionally most race sear set-ups are closer to the minimum specs to minimize lock time, and reset time. Adjustments are possible for pre and post trigger travel in addition to the min. 0.020 for the hammer hooks. The arc and diameter of travel has been reduced to a minimum, and hammers similar to the Koenig have been designed for this reduced geometry. Some frames such as the STI have been machined also with a different clearance which does not allow enough travel/pivot of the disconnector at the upper middle point, and necessitate the disconnector to be ground some to allow trave/clearancel of the sear for the half cock. SVI have a little more clearance. This is not a defect or oversight, just a design idyosincracy. This is where matching of the parts come in handy. Sometimes when removing too much pre-travel from the trigger while using a "fat" disconnector can remove angle of engagement travel from the sear causing the described problem.

But as has been described, and as "progress" and acceptance have dictated, it is not considered a safety concern as the distance from half cock to firing pin is normally not sufficient for ignition. So long as the half cock indeed captures the "flying hammer" with the finger "off" the trigger, then the (safety portion) job of the half cock is done. The half cock was never intended to be a "safe carry option" for the 1911, and the trigger was never intended to be activated from there either ... so why are you pulling the trigger from the half cock position???? Doing so continually can indeed damage the burnished areas of the sear with hammers that have not been fully relieved of contact points similar to the original Gold Cup sear, which the Koenig mimics to some degree but not completely. Just remember that not all parts are/were created equal in spite of modern CNC manufacturing, and will not just fall in place to perfect harmony. MAKU MOZO.