FP block vs cocked hammer and light trigger

[TiroFijo]

Gentlemen,

I understand how the FP block works when the hammer is at rest.

When the hammer is cocked, the FP block is out of the way, but it is supposed to "reset" faster than the hammer fall if you don't keep pulling the trigger. For example, the hammer is cocked and you drop the gun.

How light can you go with the SA trigger pull (and rebound spring) and still keep the FP reset faster than the hammer fall?
Is there any trick to keep this delicate balance?
Does lightening the mainspring also delays the hammer fall and gives a light rebound spring more time to reset the block?
Are super light SA triggers inherently unsafe if you drop a cocked gun?
How can you test the FP function in this case?

Thanks in advance

 

[WR Moore]

The block is powered by the rebound spring. You're getting into dangerous territory here. Before you reduce spring pressures that much, you've got a single action pull that's UNSAFE FOR ANY USE!!!!

I'm not referring to drop safety, I'm referring to anyone handling the weapon, under any circumstances whatever. You need to define your terms about what weights you're referring to. If you want 'thought controlled trigger' get a free pistol or a TC Contender. The TC uses a set type trigger that can safely be reduced to near nothing.

To check the function of the safety block, verify unloaded weapon and no ammo in the same room. Recheck the weapon. Then, with the empty weapon cocked, place a dowel rod or pencil down the barrel to rest against the breech face. At that point, holding the hammer, pull the trigger and allow the hammer to move forward slightly. Release the trigger, then the hammer. If the dowel/pencil isn't launched, the safety block intercepted the hammer. Note: you'll need a 5/16" (8mm) dowel assuming you have a .38 caliber weapon.

Second note: you can reduce a S&W revolver to very close to 1 kg single action and still have the safety block function as designed. However, this involves delicate work beyond simple spring changes. BUT DOES NOT INVOLVE TOUCHING THE SINGLE ACTION SEAR SURFACES! 1.5-2 kg would probably be better for most usage. The reader assumes all liability with respect to my comments.

 

[TiroFijo]

Thanks a lot,

I was not thinking about ultra light triggers, and not planning to work on my revolvers just now. The question was of a technical nature to better understand the innards.I don't plan to cut coils or put an ultra light rebound spring.

A 1.5 - 2.0 kg SA trigger pull is 3.3-4.4 lbs, and most S&W revolvers I've seen come from the factory just like that. I was asking how much below 3.3 lbs can you go, and the modifications involved, and still have a flawlessly working FP block.

In the test you mention: "holding the hammer, pull the trigger and allow the hammer to move forward slightly. Release the trigger, then the hammer." It seems to me that if I drop a cocked revolver the hammer is back, and if the hammer slips the SA sear both hammer AND trigger start the forward race at exactly the same time, so it seems this test won't duplicate this event.

 

[scooter123]

I've done some testing and the rebound spring actually has very little effect on the Double Action trigger pull but a rather distinct effect on the Single Action trigger weight. However, the range of that effect is limited. Typically a brand new S&W with the factory 16 lbs. rebound spring will have a SA break of 4.5 lbs. out of the box and level out at 4.0 lbs. after it's been fired around 500 to 1000 times in single action. Swap in a 14 lbs. rebound spring on a revolver with some use on it and the SA break will end up just a hint over 3.0 lbs. Go to a 12 lbs. rebound spring and you'll see the SA break drop to just a hair over 2.5 lbs. Now, there are 11 lbs. rebound springs available but I've found that the 12 lbs. springs are a bit borderline for a reliable and useful reset, on some "tight" actions the trigger won't reset and on most the trigger reset is slow enough to impede rapid fire. I also don't like triggers lighter than 3 lbs. in either a rifle or handgun, so my standard choice for a rebound spring is the 14 lbs. spring.

In order to get the single action trigger below 2.5 lbs. you have to use a procedure that I consider outdated and unwise. That is you have to stone the sear on the trigger to what I call an "assist angle" so that the sear notch on the hammer is effectively sliding downhill. Do that and you can produce a single action break as light as you desire, even down to a foolish 1/4 lbs. The problem with doing this is twofold. First, you place all of the wear on the sear surface on the hammer on the very tip of the sear, so it time that hammer will develop Push Off. Second, IMO anyone who takes a handgun trigger below 2 lbs is an IDIOT. Super light triggers are an invitation to an unintended discharge and can be dangerous in poorly disciplined hands.

 

[armorer951]

Modifying in the way Scooter cautions about also creates HUGE liability issues for the gun owner. Such practices are unnecessary and inherently unsafe, and cannot be defended in court.

 

[TiroFijo]

Excellent information, thanks.

I'm specially interested not only in a safe trigger were the SA sear catches the hammer in a secure way, but I also want to keep the FP fully operative even in the event when the gun is dropped with the hammer cocked.

There is a sort of "race" forward between hammer and FP block when the hammer is cocked, the trigger is not held to the rear by the finger, and for some reason (a drop, knock, etc.) the cocked hammer slips the SA sear.

If everything else is still stock, will a 14 lbs rebound spring still yield a safe, fast resetting FP block in the event that a cocked gun is dropped, as described above?

Does lightening the mainspring also delays the hammer fall and gives a lighter rebound spring more time to reset the FP block?

Do S&W SA sear/hammer engagement geometry, as it comes from the factory, has (using 1911 terminology) a "neutral" angle, or positive (in this case the sear has to move back the hammer a little bit while rotating)? I agree a negative angle would be an accident waiting to happen.

 

[armorer951]

hammer block, etc

Notwithstanding the importance of the hammer block, the primary safety preventing accidental discharge is the relationship between the hammer seat on the rebound and the rebound seat on the bottom of the hammer. When at rest the hammer is prevented from moving into battery by this "seat" on the rebound. This seat also interceeds if the weapon is dropped. In this scenario, both the hammer and the trigger race forward. In a properly tuned revolver, the trigger and rebound slide reach this resting point first, impeeding the travel of the hammer forward into the frame, and prohibiting the hammer nose or FP from striking the primer. This is one reason why maintaining proper spring tension and set up is so very important.

 

[WR Moore]

Thanks a lot,
In the test you mention: "holding the hammer, pull the trigger and allow the hammer to move forward slightly. Release the trigger, then the hammer." It seems to me that if I drop a cocked revolver the hammer is back, and if the hammer slips the SA sear both hammer AND trigger start the forward race at exactly the same time, so it seems this test won't duplicate this event.

What you state is true. However, you have to disengage the hammer & trigger sear to produce the condition that concerns you without the risk of damaging things. While this test gives the hammer a slight head start, it does verify the proper operation of both the safety block and the interface between the hammer & rebound slide the last gent mentioned. It's what amounts to a worst case scenario.

I will also quibble with Scooters comment that the trigger return/rebound spring has little effect upon double action.

 

[TiroFijo]

WR Moore, can the "hammer cocked, gun dropped, hammer escapes the SA sear" scenario be replicated by simply tapping the trigger on a cocked gun? In normal shooting the finger keeps the trigger (and FP block) to the rear, but it seems to me that if I just quicky and gently tap on the trigger the "race forward" of both hammer and rebound slide+FP block will more closely replicate what happens in the scenario mentioned.

 

[armorer951]

You can test proper/safe operation by cocking the gun SA and then tapping the trigger face with a pencil....be sure to check that the weapon is empty and pointed in a safe direction.

 

[TiroFijo]

Notwithstanding the importance of the hammer block, the primary safety preventing accidental discharge is the relationship between the hammer seat on the rebound and the rebound seat on the bottom of the hammer. When at rest the hammer is prevented from moving into battery by this "seat" on the rebound. This seat also interceeds if the weapon is dropped. In this scenario, both the hammer and the trigger race forward. In a properly tuned revolver, the trigger and rebound slide reach this resting point first, impeeding the travel of the hammer forward into the frame, and prohibiting the hammer nose or FP from striking the primer. This is one reason why maintaining proper spring tension and set up is so very important.

Thanks, it is precisely the balance of rebound slide spring force vs everything else what I'm trying to find out:

How light can you go on the rebound slide spring, all other things kept the same, as comes from the factory? Do we all agree on Scooter123 suggestion of 14 lbs as a minimum?

Does a weaker mainspring (or lower tensioned) makes for a slower hammer fall, perhaps enough to allow an even lighter rebound spring and still keep the FP block resetting faster than the hammer fall?

Are there any other tricks involved in having a sub 3 lbs SA trigger and still keep the FP bock fully functional? This last question is mostly of academical nature, since I don't plan to do it.

Thank you all for your patience with me, gentlemen

 

[WR Moore]

How light can you go on the rebound slide spring, all other things kept the same, as comes from the factory? Do we all agree on Scooter123 suggestion of 14 lbs as a minimum?

Not really sure. The factory used to teach armorers that 1 1/2 coils could be taken from the trigger return spring without affecting anything. I used to use a process I'm not going to describe further to shorten factory springs to a length I found acceptable by experimentation. Wolff spring packs supply a selection of reduced power springs that can be used on a try and see basis.

Does a weaker mainspring (or lower tensioned) makes for a slower hammer fall, perhaps enough to allow an even lighter rebound spring and still keep the FP block resetting faster than the hammer fall?

In short, yes. The factory suggestion was to not back the strain screw out more than 1/2 a turn. Obviously, a whole bunch of people have done more than that.

Are there any other tricks involved in having a sub 3 lbs SA trigger and still keep the FP bock fully functional? This last question is mostly of academical nature, since I don't plan to do it.
Thank you all for your patience with me, gentlemen

Yep, but for liability and proprietary process reasons I'm not getting more specific. I worked primarily to reduce DA pull, all SA reduction was a side benefit.

 

[tomcatt51]

Maybe someone can enlighten me.

I understood the hammer block was added to prevent an impact on the hammer (hammer forward) from forcing it forward causing an AD. Without the hammer block this can be done but requires damaging the gun for it to occur.

The rebound slide has always been there to prevent the "slips off the sear" discharge.

"Bump" the trigger (hammer cocked) and the rebound slide (and the trigger) "races" the hammer forward and the rebound slide is supposed to prevent the hammer from moving fully forward. The rebound slide does this without benefit of the hammer block. If the rebound slide doesn't get forward before the hammer, the hammer block doesn't get moved into a position to do anything either.

Centennials (no exposed hammer) don't have the "extra" hammer block. They rely soley on the rebound slide.

Am I missing something?

Yes, I'm familiar with the Navy "dropped gun" incident that resulted in adding the hammer block.

 

[WR Moore]

The Centenial also doesn't have an exposed hammer. Therefore, it couldn't have the hammer forced through the interference with the rebound slide. Also, there's no single action capability.

Looking at the Brownell S&W part list, the hammer block has been discontinued from the factory.

 

[tomcatt51]

Looking at the Brownell S&W part list, the hammer block has been discontinued from the factory.

True. Guess I won't be able to replace my "broken" ones.