Trigger Sear Offset?

[Diving Gecko]

Since I am setting out to make my own handle, trigger and possibly barrel I have been trying to figure out the exact geometry of the "classic Italian trigger" and especially how much of an offset the sear lever has in the barrel.

We know that the sear pivots around a pin that sits a bit below the center line of the barrel - but what we will try to figure out in this thread is, just how much lower? And what governs it?

Also, this is a rehash of my investigation into this from my very long Mirage build-log but that was inconclusive and I thought the subject deserved its own thread in case some day, someone else comes looking for this info.

We are talking about the classic sears in this pic:

(Disregard the notes on the barrel - it's from a modification I did so a Salvi barrel would fit in a Mares handle and it was the only pic I could find showing the sear levers)

I modeled the sear as carefully as I could:

One important assumption - and I will tripple check this soon - but as far as I could measure, the top edge of the hook sits at the same height as the pivot point:

Another assumption I am making is that the sear was designed to sit horizontally when cocked (under load). Judging from some older posts by Pete, this would be ideal.

The simplest I can think of is that the old Italians intended for the sear to touch the stem of the piston tang and to have maximum engagement. Like so:

And if those assumptions are correct, then it would be the diameter of that stem that dictates the offset from center. A thicker stem would mean the sear has to sit lower in the barrel.
And it would all be as simple as the offset being half of the stem diameter.

Let me add some measurements to make that more clear:

As you can tell, I made the tang stem 4mm and the flange 8mm but here's the thing, I don't actually know if 4/8mm was the standard intended?
I don't have any old stock pistons on hand here to measure and my newer, more optimized pistons have thinner stems and flanges.

Let's for now assume that another standard stem size could be 3.5mm. Then the offset would be 1.75mm and it would look like this:

So, let me ask for a bit of help:
If any of you have some older stock Mares, Seac, ScubaPro, etc pistons and calipers on hand, could you please check the stem diameter and the flange, too? (So, the 3.5/8mm dimensions in the example pic just above).

And of course, also point out if my thinking up until now is flawed.

In a later post, I will probably get into how thinner stems and flanges on custom pistons start affecting the geometry, but doing that now would just confuse matters.
For now, I am interested in whether we can nail down the original design intent

 

[Diving Gecko]

Salvimar Predathor Piston
Let me add the first data point and it's not pretty...

I found a stock Salvimar piston. I pulled it out of a friend's Predathor that was bought around 2015.

The stem is 5mm:

The flange is 8.5mm:

But the pivot offset in the barrel is not 2.5mm. I measured it on the CNC to be very close to 2.0mm... Which means the sear would sit like this when cocked:

So, it seems we may have a tilted sear, which Pete has warned against. But at least we have a lot of engagement as the flange is quite wide.

If we want the sear to sit level in this barrel, the stem would have to be 4mm or the sear should be lowered to 2.5mm. Maybe there was a standard but at some point the piston tang design changed or the offset did and the engineers lost track?

Detour/Tiny Rant
Now, at the risk of going on another rant, the more I measure, the more I realize there's some weird stuff going on in some of these guns. I have previously stated that from what I have gathered, Salvimar and Mares are both guilty of bad o-ring groove designs. Granted, I am far from an engineer but it's my understanding that you always need "free space" in the groove for the ring to expand into.
But e.g. on Salvimar's otherwise nice Predathor barrels the o-ring groove for bulkhead is simply too narrow to allow that. It's about 1.75 which constrains the ring on the sides where it should have been free to move.
And now, I see the same on this stock piston:

At least the front groove is wider at 2.1mm which kinda starts being enough free space for a 1.78mm ring being compressed at 20%. But even if they intended to use 1.5mm rings, the metal groove is still too narrow.

The point is, if my understanding of o-ring groove design is indeed correct, there are quite a few little instances of imperfect design decisions in these guns. And perhaps the sear offset and the tilted sear is just another example of this...