Not a lot to go on there, but at least enough to start the discussion.
Your other thread's title suggested that you thought the sear was damaged. That would not be my first suspicion, based on your description of the issue, but it should be easy enough to confirm by inspecting your sear. Any damage that would impede the travel of the ejector would be readily apparent on visual check. The sear's orientation is nearly identical when it is sitting in the safety-catch or the cock-notch, so anything it would be doing to impede the ejector should show itself in both conditions.
Assuming the sear checks out. The four most likely culprits, in my opinion, would be, in order:
1 - The operator. Don't be offended by this. The operator is the least reliable part of any quality gun. Placing false confidence in this part can easily lead the gunsmith to chase repairs of things that aren't broken. Are you positive that it is behaving differently, and are you positive that you're doing it the same way you always have?
2 - The ejector. Is it cracked or bent? Being a stamped part, it will hide minor damage (slight bends, small cracks) better than most MIM of billet parts.
3 - The sear pin. Is it bent? That would change the relative positions of the ejector and the slide, and would vary slightly with each reassembly, giving you random results after each service.
4 - The sear spring. Is the bend on the top of the left-most (op's position) leaf damaged or bent out of its original position.
The ejector is free to travel further forward when the hammer is on the safety catch than it is when the hammer is cocked. This is because of the clearance between the hammer and the sear spring. The bent end of the ejector's leaf of the sear spring bottoms out against the hammer. When the hammer is cocked, the sear spring is stopped by a portion of the hammer that is further from the axis of the hammer pin than when the hammer is on the safety-catch, so, when the hammer is cocked, the ejector cannot be pushed as far forward.
I assume most people install the slide with the hammer cocked because of the reason that you cited; it's easier to reach the ejector with the hammer out of the way. When the hammer is cocked, the ejector can just barely travel far enough to allow the slide to pass over it. This should not be a problem, unless the ejector becomes bent, cracked near its pivot hole, the pivot hole becomes enlarged, or the sear pin becomes bent. A small change in any of these dimensions could make enough of a difference to turn that barely-enough-travel into not-enough-travel.
If the ejector, sear spring, and sear pin all check out, I'd go right back to the operator again. Because of a couple peculiarities of the ejector's geometry, and since it has so little over-travel when the hammer is cocked, an almost unnoticeable difference in when and how you depress it during reassembly could make it seem like it can't be depressed enough to allow it to clear the slide.
There was a lot more information to go on, but I had the two issues separated since I didn't realize at the time how related they actually were. When Sig moved it into this one, I deleted it so this just covered this. I will post my thread I had up about fearing I bent the sear or pin, below.
1 - I am 100% positive there is an inconsistency. I used to never dry fire the gun on breakdown, simply leave the hammer back, do a basic clean with the slide off, and put it back, hammer back the entire time. Now, like I said, I have to de-cock to at least the half cocked position, or it would not be possible for the slide to be put back.
2 - Took everything apart late last night, examined the ejector and it looks fine to me. Certainly no cracks, and doesn't look bent.
3 - Sear pin is not bent as far as I can tell.
4 - Again, not as far as I can tell, but with this piece I think it would be a little harder to notice.
Thank you for the information! Explained very well. Something must be a little off and I just can't tell by looking. I am thinking maybe the sear or sear pin may have such a minute bend that I can't tell. But there is definitely a difference. It was easy to move the ejector enough for the slide to pass originally, now, I feel like I would have to put a LOT of pressure on it, and possibly break it to get it to pass without decocking.
Playing around with mine, I was able to induce two different snags that, while I was intentionally trying to do it, could easily be done by mistake.
1 - On the left side of the ejector, where the tip meets the body, there is an abrupt shoulder that can be caught on the left rail. Unintentionally biasing the ejector left while depressing it could make it seem like the ejector is at the end of its travel.
2 - On the top of the ejector, where the tip meets the body, is another abrupt angle. If the ejector is not fully depressed when the firing pin retainer tries to pass over it, that corner can hang up on the firing pin retainer. In most cases, the firing pin retainer causes the ejector to roll further downward and out of the way, but if you catch it just right, it will feel like a hard-stop. If you're holding back on the slide, while trying to depress the ejector further, the two motions end up fighting each other, making it feel like the ejector is at the end of its travel. In both cases, easing the slide forward slightly and trying again corrected it.
To see if it is an operator issue, meaning that you're doing it just slightly different than you did successfully in the past, try using a tool to depress the ejector, and depress and hold it down well in advance of the firing pin retainer reaching it.
1 - I am aware of this, that is not what is going on here. Even if I bias it right enough that it is in the channel for the hammer instead of going under the slide a half inch further back or so, it still won't go forward far enough. (mine has had a lot of play from the beginning, this is something I even contacted sig about and they looked at when the gun was in for a new tritium sight. This inconsistency started occurring after getting it back.)
2 - I can recreate that scenario as well, but again, not what I"m regularly experiencing.
Both of those scenarios, with the hammer de-cocked, I can recreate and remedy by like you said, just trying again gently. However, with the hammer cocked, no matter what, it doesn't move forward enough to let the slide pass. This is the case when using my finger, or using a pick.
Here was my other post, that at the time, I thought was unrelated. Might provide some insight into me possibly bending the sear or sear pin slightly. There is definitely something happening here, I'm no gun smith, but I fire and clean the gun regularly, and it is definitely different than it was before, whether it's related to a damaged part or not.
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After re-assembling the Main Spring, Hammer and Strut, and Hammer Pin, I did a quick function check. I realized that I couldn't get the Hammer to lock in the cocked, or half cocked position. I put a good bit of pressure on it attempting only one more time to cock the hammer. Then after nothing happened, I realized I must have done something wrong. Guess I should have examined the position of the sear better when I took it apart, as it was positioned incorrectly, so the hammer was never going to engage those grooves on the sear. Best way to explain, was instead of the sear being vertical, it was 90 degrees different, laying horizontally, so the hammer would have just been resting on top of it I believe (or maybe not, not sure how much room there would be between them).
It only took a second to realize and remedy, but I guess I'm just a little worried about the amount of pressure I put on the hammer with the sear positioned incorrectly. I can't picture or see exactly how the hammer would have been pushing on the sear when it was installed wrong, but I just want to know if it's possible I could have bent or compromised any integrity of it. It's functioning fine, I have shot it many times since, and I also leave it cocked and locked and obviously nothing has gone wrong yet...
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Nothing was mentioned about the ejector above, as I didn't know the two issues were so closely related at the time. Again, thanks for the info thus far. I'm wondering if even though I don't see any damage to the sear or pin, if I should get new ones simply to put my mind at ease. If they fix the problem then obviously something was damaged.