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Discussion Starter · #1 · (Edited)
I finally decided I love the FS2000 enough and hate the trigger pull enough to start looking for ways to do something about it. Greasing the trigger, trigger rod, and hammer group and polishing the trigger rod have limited effect. Adding Dr. Coffee’s Neu-Trigger is a good step but we all know that the real problem is the in-axis sear springs.
Short of completely redesigning the trigger mechanism and the hammer group or adding some sort of electric / pneumatic / hydraulic assist in the big open volume below the hammer group (pneumatic assist seems the most likely course there), the only solution is to change the springs.

There are a few obvious problems with cutting coils from one end of the springs, which have been discussed in other threads:
1. The spring ends no longer have closed ground ends to provide even pressure no matter how the springs rotate.

2. If the springs rotate, the Free Length may suddenly vary by as much as a coil length, if cut from the front. If cut from the back, it is possible a spring could, theoretically, rotate out of the housing, or at least attempt to. Much more likely, the affected sear leg would jam, preventing the gun from firing.

3. The Free Length is reduced, possibly compromising the sear being pushed forward enough to completely catch the hammer once released from the disconnect. This could significantly increase the chances of a butt bump Accidental Discharge, especially when combined with effects from #2.

4. Completely removing one spring produces significantly asymmetrical forces on the sear.

So I decided to try replacing the springs with ones of appropriate length, but reduced force.

Here are the results of my first round of tests.

A Lyman digital pull gauge (12 lb., 0 oz. max) was used to measure the pull and average the trials.

All springs have closed ground ends.


The modified hammer group is a Gen 2 as I could not bring myself to modify my only Gen 1 Hammer Group.


Spring #

1

2

3

4

5

6

7

8

9

10

OD (in)

0.260

0.260

0.300

0.300

0.300

0.300

0.266

0.281

0.250

0.296

ID (in)

0.196

0.196

0.240

0.240

0.236

0.236

0.196

0.209

0.190

0.220

Free Length (in)

1.125

1.125

1.130

1.130

1.130

1.130

1.160

1.190

1.160

1.130

Rate (lbs/in)

?

?

6.500

7.600

8.100

9.500

12.000

8.400

9.900

16.000

Max Load (lbs)

?

?

3.400

5.000

4.100

6.100

6.600

4.200

6.000

6.600

Solid Height (in)

0.481

0.481

0.290

0.290

0.330

0.330

0.600

0.690

0.390

0.440

Pull (lbs, oz)

8, 10

9, 9

6, 7

7, 12

7,10

9, 6

10,12

9, 7

10, 11

>12, 0

Note

1

2

3

3

4

4

5

5

4, 6

5

Notes:
1. Gen 1 Hammer Group, several hundred rounds, greased, Neu-Trigger installed, OEM springs
2. Gen 2 Hammer Group, new, no modifications, OEM springs
3. Solid height is short. When completely compressed, the hammer could rotate sufficiently to lock against the bottom of the sear carriage
4. Solid height just long enough to prevent locking
5. Solid height OK
6. ID too small. Had to hand fit to find a pair that worked

Does this compromise the safety margin of the sear hold force? I am sure it does to some extent. An unscientific slamming of the butt of the hammer group against my work table did not produce a release with spring set 3 (6lb,7oz pull) installed. Hooking my gauge, as best I could, directly onto the sear produces a pull of 7lb, 8oz (78% of triggerpull) to release the hammer with spring set #2 and 4 lb, 15oz (77% of trigger pull) to release the hammer with spring set #3. I am not planning on taking this gun with this modified hammer group on maneuvers.

I intend to test fire the gun tomorrow with the modified hammer group and spring set #3.

Further spring set tests will use spring set 3 as a center. At some point I will add the Neu-Trigger.

Anyway, first pass at some tests. Thanks for any thoughts / feedback /suggestions.

Spring Comparison Setup.jpg
 

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All of this is great information. In the end one has to wonder why FN went with the springs that it did.....Was it a design consideration or a supply consideration...

Keep uo the testing as you may just find the sweet spot everyone is looking for.
 

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All of this is great information. In the end one has to wonder why FN went with the springs that it did.....Was it a design consideration or a supply consideration...
It's a safety/liability issue, considering the fact the weapon was originally designed for the world's military's, not civilian shooters who want match trigger pull weights in military look-alike weapons.

-SS
 

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Discussion Starter · #4 ·
It's a safety/liability issue, considering the fact the weapon was originally designed for the world's military's, not civilian shooters who want match trigger pull weights in military look-alike weapons.

-SS
Sarge is, of course, correct. It's a little like buying a heavy duty truck to haul 2 tons of concrete block around the construction site and then complaining that you aren't winning stock car races with it on the weekend no matter how you tune it up. Or perhaps like complaining that your tuna just won't soar like an eagle no matter how many feathers you glue to its hide, and it doesn't swim like it used to either...
It's a bullpup, it has the inherent advantages and disadvantages of a bullpup.
You either have to pull the hammer away from the sear or push the sear away from the hammer. Pulling the hammer forward while pulling the trigger backward requires a rotating lever or a pulley system. The rotating lever gives the opportunity for mechanical force multiplication. You pull the trigger back 500 thousandths with 3 lbs of force and get 100 thousandths of forward hammer movement with 15 pounds of force. The few hammers I have looked at have fairly narrow hammer / sear engagement surfaces. You don't need a lot of movement to release the hammer. The FS2000 engagement surface is huge in comparison. That, along with the heavy springs, produces the required safety margin so that it doesn't accidentally discharge while being banged around under battlefield conditions. That was the design choice for the maximum safety using the simplest, thus least failure prone, mechanical system within the design requirements of an environmentally sealed bullpup system. You push the sear back from the hammer using a straightforward rod and sear carriage assembly with in-line springs to resist the push and return the sear to its forward position. Simple, reliable, and you can break it down in the field without unhooking mechanical linkages.
Any fiddling around with the current design reduces the safety margin and you have to accept that risk. If you are never going to subject the gun to battlefield conditions then the design parameters change and a reduced safety margin may, in the designer's judgement, be acceptable.
Short of starting from scratch and redesigning the firing system with a more complex system of non-axial safeties or some sort of force multiplier (lever, pulley, or mechanical assist), we are left with reducing the sear carriage spring force and reducing hammer / sear engagement surface friction.

I am enjoying my FS2000 for what it is (work truck / tuna) and for the, to me, elegant form. Being an engineer, I can't help but tinker with what makes it go.
 

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I've been finding this very interesting. I can't wait to see what the final results will be. Do you have access to manufacturing equipment? I have a few ideas I could bounce of you, i'm local to Columbus as well
 

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Discussion Starter · #6 ·
Quick range report from the weekend

Shot about 60 rounds with the modified hammer group. No failures. Nice smooth pull. Only "criticism" might be that with the original setup I could tell when I was getting ready to fire by a tightening of the trigger. This time my relatively indelicate finger never knew at what point it was going to fire. I hope to shoot again this weekend and will spend less effort worrying about whether it will cycle correctly and more on the feel.
 

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Discussion Starter · #7 ·
I've been finding this very interesting. I can't wait to see what the final results will be. Do you have access to manufacturing equipment? I have a few ideas I could bounce of you, i'm local to Columbus as well
I am not sure there will be a "final result". It is, as the saying goes, the journey that is important. Have your people call my people :wink: (PM me if you like).
 

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Discussion Starter · #8 ·
Anybody notice that someone from Chandler, AZ is offering a "magic" (his word) trigger lightening job for the FS2000? He is advertising it as just over 5 lbs pull. Wonder if he's replacing the springs? I had no knowledge of this prior to today, have no knowledge of what he is doing to achieve this "magic", and am not associated with him in any way, in case anyone is wondering.
 

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Anybody notice that someone from Chandler, AZ is offering a "magic" (his word) trigger lightening job for the FS2000? He is advertising it as just over 5 lbs pull. Wonder if he's replacing the springs? I had no knowledge of this prior to today, have no knowledge of what he is doing to achieve this "magic", and am not associated with him in any way, in case anyone is wondering.
Met a guy at the range today who had that trigger job. I fired his FS2K and it was smooth. Looking at the trigger group it was apparent he had replaced the springs.
 

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Discussion Starter · #11 ·
How do you switch the springs?
You have to remove the sear carriage (I am making that name up as I don't know any official name) from the hammer group boat (housing?). The original springs are under slight compression so as you slide it out they will pop off if you don't capture them. Once the carriage is out you slide the OEM springs off the arms at the rear of the carriage and slide new ones on. Reassemble and, viola (yes, I know... it's an inside joke), you have a non-regulation, potentially dangerous, hammer group.
N.B.: Modifications (such as this) that significantly alter the function of any gun should only be performed by competent personnel with proper training.
 

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Discussion Starter · #12 ·
Met a guy at the range today who had that trigger job. I fired his FS2K and it was smooth. Looking at the trigger group it was apparent he had replaced the springs.
Thanks for the information. I guess there really is nothing new under the sun.
Did it appear that any other modifications were done as part of that job?
Did the hammer group have a Neu-Trigger installed or had it been greased / oiled?

Thanks again for the report.
 

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Discussion Starter · #13 ·
Range Report using Hammer Group with #3 Spring Set

Put 90 rounds through it today. No failures. I am still surprised when it fires since I've gotten used to the feel of the original "concrete block" trigger. I let my wife fire it since she has fewer preconceived notions about it. She reports the trigger feels much lighter and does not fatigue her trigger finger. Remember, this is a new hammer group that had zero rounds on it when I started last week, so total rounds on it is under 200. Hammer group is dry, no oil, no grease. No Neu-Trigger. It feels a little gritty / jerky but I assume that will smooth out once I lubricate it and, finally, install a Neu-Trigger.
At 50 yards, with generic XM855 style ammo and light variable cross winds, shooting 6 to 8 round trials, my wife was making 2" to 3" groups using a couple of shooting bags on a piece of 3/4" plywood on a couple of sawhorses. EOTech 512 optic, no magnification. She has a better eye than I do and, like most women, better fine motor control so I let her do this sort of thing once I am sure nothing is going to go wonkie.

Pull test with the Lyman is now showing a pretty consistant 6 lb, 9 oz (-1 oz, +2 oz).

Based on these initial tests, I have a new set of springs on the way that start a little above set #3 and go down from there.

Thoughts, comments, suggestions, critiques welcome.
 

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Thanks for the information. I guess there really is nothing new under the sun.
Did it appear that any other modifications were done as part of that job?
Did the hammer group have a Neu-Trigger installed or had it been greased / oiled?

Thanks again for the report.
Can't say about the Neu-trigger as I have no idea what that is. The trigger group appeared to not have been greased / oiled.

Edit: Checked out the Neu-trigger web site and no there was none.
 

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Discussion Starter · #17 ·
Spring set #3 tests

My wife, a friend, and I worked on testing the FS2000 with the modified hammer group using the #3 spring set. No lubrication, no Neu-trigger.
The pull is a lot easier at 6 lb, 9 oz. But it definitely has a creepy, twangy feel to it that I attribute to the lack of anything to smooth the movement.

At 50 yards, my wife had the best grouping, 1.5 inches (3 MOA) for an 8 shot grouping. We were using generic 62 grain XM855 ammunition with calm winds and an EOTech 512 sight with no magnification. We were using (as before) a couple of saw horses with a 4' x 4' 3/4" piece of plywood on top and a couple of shooting bags as rests.
If anyone can tell me how good or bad this is generally, I would appreciate it.
 

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Discussion Starter · #18 · (Edited)
Next Spring Set Tests

Second round of tests. Numbers 1 and 2 are the original OEM Gen 1 and Gen 2 hammer pack tests from the original tests. Number 3 is the “winner” from the first round of tests.
The test bed modified hammer group is a Gen 2 as I could not bring myself to modify my only Gen 1 Hammer Group.

Spring #

1

2

3

11

12

13

14

15

16

17

18

19

20

OD (in)

0.260

0.260

0.300

0.300

0.300

0.300

0.296

0.240

0.250

0.240

0.300

0.300

0.240

ID (in)

0.196

0.196

0.240

0.236

0.240

0.240

0.236

0.192

0.190

0.192

0.248

0.248

0.192

Free Length (in)

1.125

1.125

1.130

1.250

1.250

1.250

1.190

1.130

1.250

1.250

1.130

1.250

1.130

Rate (lbs/in)

?

?

6.500

7.300

6.600

5.600

5.000

4.900

4.800

4.600

4.600

4.300

4.200

Max Load (lbs)

?

?

3.400

4.100

5.000

3.400

3.400

3.400

2.400

3.400

3.300

3.300

2.300

Solid Height (in)

0.481

0.481

0.290

0.360

0.330

0.330

0.390

0.280

0.750

0.300

0.230

0.240

0.280

Pull (lbs, oz)

8, 10

9, 9

6, 9

10, 6

9, 8

8, 0

6, 13

5, 10

7, 15

6, 14

5, 14

6, 9

5, 2

Note

1

2

3

3

3

3

3

3

7

3

3

3

3

Notes:

1. Gen 1 Hammer Group, several hundred rounds, greased, Neu-Trigger installed, OEM springs
2. Gen 2 Hammer Group, new, no modifications, OEM springs
3. Solid height is short. When the sear carriage is compressed, the hammer could rotate sufficiently to lock against the bottom of the sear carriage
4. Solid height just long enough to prevent locking
5. Solid height OK
6. ID too small. Had to hand fit to find a pair that worked
7. Solid height is just short enough to release hammer


Thoughts,comments, suggestions, critiques welcome.

 

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Was surfing GB and found HDD now has a all aluminum hammer for PS90/FS2000s.
 

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Was surfing GB and found HDD now has a all aluminum hammer for PS90/FS2000s.
I got two of these and the sear from purplenv and planned on t.rying to get it chromed if possible with a neu trigger to see if it helps with the trigger pull. The aluminum hammer looks just like the fs2000 hammer and is about the same weight add well, lookslike see good product. I will let you know how it turns out after I use it a few times.
 
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