Pistol sear spring

[Pofoo]

I'm working on a Star Mod SS 380, which is a bastardized 1911 design. It looks like a 85% 1911 without a grip safety. It uses the slide, frame, and barrel link top end, but the fireing mechanism is different.
This one has a pretty hard trigger pull. The way it works, is that there is a coil spring in the trigger that the trigger bar is cammed off of. This acts as the trigger return spring. There is also a flat spring that runs up the back of the grip to push on the sear. Between the 2 of them, they supply the spring pressure of the trigger. I cut off a coil on the trigger spring and it now returns well with less pressure. I've stoned the hammer and the sear for a smoother and shorter release. The sear spring is about 3/8" wide by about 2 1/2" long. I've filed along the long edges and maybe removed about 1/32" of width.
This helped, but there still seems to be more than enough pressure on the sear. With a little rearward pressure on the hammer to free up the trigger, the trigger pull is still fairly stiff.
So, the question is, how much pressure is needed on the sear? Just enough to seat it against the hammer, but not too much needed to normally retain it? Once cocked, I can release the spring pressure on the sear and the hammer remains cocked. It probably wouldn't hold if the pistol was dropped, so I definitely need some continuous pressure. Right?
Next question is how to lighten a leaf spring? I don't think I want to narrow it any more, as it fits loosely in a channel in the frame. So, that leaves thinning down the thickness. I think it could be sanded or stoned? Would it be better to do the whole length or start mid way and go to the end? What would be better for long term reliability and consistent pressure?
Thanks in advance.
Here's a schismatic of a similar pistol. Sear and spring are parts #6 & #8.

https://www.gunpartscorp.com/gun-manufacturer/star/pd-auto

[ar15barrels]

There is no "right answer" to your question.
Your spring may have significantly more strength than is necessary, but you will not know until you continue reducing the force and doing drop tests by rapping the gun with a rubber or nylon hammer and trying to get the sear to trip from impact.
Once you get that far, you need to about double your force from that point for a good safety margin.

You will need a force gauge that can pull against the spring while it's installed in the gun as this will account for the spring's pre-load as well as it's rate.
You need to be measuring the actual spring force while it's installed as you go.

Get a 2nd spring to fool with so you leave the original alone.
Mess with the 2nd spring until you over-do it and have an actual measurement force to reference.
Then work on the original spring to get where you want to be.

[drmjf]

I would get a sear spring before you try any lighting of the spring. I just did a similar star. The sear was not very heavy. With the hammer pulled back it should only be about 3lbs if checked with a trigger pull gauge. I hope this helps.

Sent from my SM-N910V using Tapatalk

[ojisan]

Keep in mind that the sear spring needs to (push the sear to) catch the hammer during recoil.
There's not much time to do this, and the whole gun and the parts inside are moving around with lots of forces going in different directions.
As Randall said, you will need about twice the tension that feels right on the work bench when dry firing.

Leaf springs can often be narrowed side to side in the middle on the arms, leaving the closed and open ends the original size so fit to the gun is not affected.

[Pofoo]

OK, great. 3 good replies.
The spring IS available through Numriches.
I do have a trigger pull gauge.
Any suggestions on stoning the spring? Full length or half point to the sear end?

[saki302]

No one could answer that unless they've worked on loads of Star pistols, which most gunsmiths won't have. Get some spares and do some trial and error.

I have tuned many 1911 triggers, but I just know when the flat spring tension feels right. I couldn't tell you how many lbs it measures on the scale. I don't have the cool tools Randall has

-Dave

[MosinVirus]

Did you also work on the sear surface that contacts the sear spring and the sear spring surface that contacts the sear? Could there be interference somewhere else?

To me it sounds like there may be other areas to look at. This is purely judging from what you have listed in the post - sear and hammer engagement surfaces stoned, and trigger spring shortened.

It has been a while since I had a Star and I don't remember how thick that sear spring is, but can it be bent to relieve pressure?

[Pofoo]

OK, thanks all.
It seems, as mentioned above, that there is no absolute answer here. As there are numerous parts involved, it's a process to go through them all. I have looked and adjusted/fitted/stoned numerous parts/springs.
I THINK that the sear spring is the last major part to work on.
Upon further research, it appears that the most common way to lighten a leaf spring is to narrow it's width towards the middle while leaving both ends full width.
I didn't use a pull gauge to start, but the trigger is now much better. Less creep and lighter let off. I'll keep playing with it. I like the idea of hitting it with a rubber mallet to make sure it stays cocked.
Thanks again for all the great answers.

[ar15barrels]

I like the idea of hitting it with a rubber mallet to make sure it stays cocked.
Thanks again for all the great answers.

Strike the FRAME to cause a large vibration in the gun, not the hammer.
Make sure you do it from different directions, particularly the ones that would cause the sear to move.

[divingin]

I wouldn't stone the spring. It's a piece of sheet metal that's heat treated, and you can't tell how deep that goes. If you're going to adjust it, just overflex it slightly in the direction you need it to move. Make sure you do a good impact test before loading the pistol (those around you will appreciate it.)