AR Two Stage Trigger Mechanically Safer than Single Stage?

[Ethan Verity]

In searching the internet, I don't think this point has been brought up before. It seems to me that most two-stage AR triggers are mechanically safer than single-stage triggers.

The single stage trigger has one sear engagement surface, and if it were to ever fail for some reason the gun would fully drop the hammer. Whereas most two-stage triggers have the primary 'two-stage' sear engagement, with the addition of a single-stage style sear engagement surface that is never actually used. If, for whatever reason, the two-stage sear were to break, the hammer would be caught by the secondary single stage sear to prevent a full hammer drop. I posted a picture below with the primary sear engagements circled in red, and pointed out the secondary single-stage sear on the two-stage trigger.


It's along the same lines as the firing pin block safety in a modern striker handgun; that second 'back up' if the sear were to ever fail. Personally, I like this design. I prefer to keep a round chambered in my defensive rifle, and chose the two stage trigger for this perceived added mechanical security benefit. I also like the feel of the two stage trigger.

 

[Slamfire]

Yes. It is a better trigger mechanism.

This is one of the finest service rifle trigger mechanism ever made. I don't know if it originated with John Garand, but here it is.



an original M14 trigger group



The same type of mechanism is found in the AK47, but that does not mean it was not independently invented.

I remember the early days of the NM AR15, and only one decent two stage trigger was on the market, the Milazzo-Krieger Trigger. Which had a fatal flaw, the sear adjusting screw would always break loose and the second stage would not hold the hammer hooks. The guys trying to hone their service rifle trigger mechanisms, sure they could achieve a fine trigger pull, but that military trigger always, and I mean always wore, and the rifles would go full auto. The original military trigger is simply not as a good design for a fine trigger pull, and it wears. A good Garand trigger will last forever, basically.

I was able to buy Armalite two stage triggers that were properly set up on my first NM AR15. The trigger weight has not changed, the final pull is excellent, and it has never malfunctioned due to wear.

 

[mcb]

I like two stage triggers in my AR also but for the trigger pull not the perceived safety aspect. I have put enough rounds through AR's and even broken a few fire controls in my time (abuse not normal use) I have never had the secondary sear do anything for me despite those failures. Buy quality fire controls that do what you want (single vs two stage) and don't sweet the rest. The number one most likely thing to fail in the fire control is the hammer spring.

 

[Demi-human]

Single (stages) for life!

I don’t like to move my glass rods a quarter inch before they break…

 

[Armorer 101]

If you keep your trigger finger off the trigger until ready to fire, it really does not matter one little bit.

 

[taliv]

The Xtreme (cg jackson) triggers I used on my bolt guns also had two sears with engagement that could be set separately.

In the case of light weight bolt gun triggers it makes sense. In the case of heavy AR15 triggers I don’t think it offers much since sear engagement isn’t adjustable.

 

[Steve S.]

I have a TS trigger on my Anschufz .22 - I am not sure that it is a safer mechanism but I do like the take-up before the release - it is like the final prep to settle in before the shot breaks .

 

[Varminterror]

If, for whatever reason, the two-stage sear were to break,

I’m not terribly convinced this is a valid failure mode to be analyzed. So the perceived redundancy is likely nothing more than well-wishing.

 

[mcb]

I’m not terribly convinced this is a valid failure mode to be analyzed. So the perceived redundancy is likely nothing more than well-wishing.

I have seen the sear/disconnector leg break off a DPMS two stage and the gun doubled when the hammer followed but then stopped on the third round hammer down. The "secondary" sear might have stopped a runway but hammer follows rarely run away and the shooter rarely react fast enough to stop the gun before it stops itself.

 

[Varminterror]

hammer follows rarely run away and the shooter rarely react fast enough to stop the gun before it stops itself.

This is largely my point. The failure mode is rare enough as it is, and the result isn’t machine gun fire to be stopped by the “secondary sear.”

Honestly, shooting and installing two stage triggers for over 20yrs, I’ve looked at that notch as a price nuisance, an extra step in production for which I’d honestly rather not have to pay in the purchase price. Not an up-feature in design, in my perspective.

 

[bihj]

I believe that if you look closely at the picture of the single stage trigger, in the area that has been circled, you will see a 'second sear'.
Kinda makes your whole argument irrelevant.

 

[mcb]

This is largely my point. The failure mode is rare enough as it is, and the result isn’t machine gun fire to be stopped by the “secondary sear.”

Honestly, shooting and installing two stage triggers for over 20yrs, I’ve looked at that notch as a price nuisance, an extra step in production for which I’d honestly rather not have to pay in the purchase price. Not an up-feature in design, in my perspective.

Agreed. The only reason for that vestigial feature in most two stage triggers is to ensure you can't put the selector to the safe position with the hammer down. If you allow that to happen the sear on the hammer can't get by the seat hook on the trigger and bad things can happen. Breaks parts and jams bolt carriers.

 

[Ethan Verity]

I believe that if you look closely at the picture of the single stage trigger, in the area that has been circled, you will see a 'second sear'.
Kinda makes your whole argument irrelevant.

I only see one sear in the area I circled, not two.

I have seen the sear/disconnector leg break off a DPMS two stage and the gun doubled when the hammer followed but then stopped on the third round hammer down. The "secondary" sear might have stopped a runway but hammer follows rarely run away and the shooter rarely react fast enough to stop the gun before it stops itself.

Interesting. But I was thinking this would help make the gun safer if the sear breaks when it's not being fired... less so if the sear breaks when the trigger is back. Just like the hammer pin block on a modern striker fired pistol will stop the firing pin if the sear breaks when the trigger is forward (not firing, but maybe dropped or something). Is the two stage more drop safe? Maybe it doesn't make a difference, I don't know.

 

[bihj]

I only see one sear in the area I circled, not two.

 

[bihj]

In the first picture the hammer is fully cocked (exposing the 'second sear). The second picture shows the hammer not fully cocked and the 'second sear', within the circle, is somewhat hidden behind the spring.

 

[Ethan Verity]

In the first picture the hammer is fully cocked (exposing the 'second sear). The second picture shows the hammer not fully cocked and the 'second sear', within the circle, is somewhat hidden behind the spring.

Ah, I understand what you're thinking now. But no, the single stage only has that one sear as circled, there is not one hiding behind the spring. Both hammers in the original picture are fully cocked for that design of trigger.

A disassembled single stage for reference, pictured here, clearly shows the single sear.

 

[bihj]

Please explain why the second trigger isn't fully cocked on the same sear as the first (which would fully expose the other notch)

 

[Ethan Verity]

Please explain why the second trigger isn't fully cocked on the same sear as the first (which would fully expose the other notch)

This video (not mine) does a great job of explaining how both the single, and two stage AR triggers work.

 

[Varminterror]

In the first picture the hammer is fully cocked (exposing the 'second sear). The second picture shows the hammer not fully cocked and the 'second sear', within the circle, is somewhat hidden behind the spring.

Those pictures are different fire control groups altogether.

The single stage trigger only has one sear, while a two stage could have a redundant secondary sear, as described by the OP.

 

[Ethan Verity]

If you keep your trigger finger off the trigger until ready to fire, it really does not matter one little bit.

My post is about the possibility of one fire control group potentially being safer if a mechanical failure of the sear were to happen, perhaps from a hard drop, wear, or metal fatigue... trigger discipline is irrelevant to this point.

 

[Varminterror]

My post is about the possibility of one fire control group potentially being safer if a mechanical failure of the sear were to happen, perhaps from a hard drop, wear, or metal fatigue... trigger discipline is irrelevant to this point.

The ONLY relevant failure mode which could cause a top-mounted 2 stage sear to break is metal fatigue or materials issue (inclusion fracture, embrittlement, etc).

The end result would be doubling or an AD during charging. Effectively, a single unintended round will fire when the hammer is released by the fracture, then the hammer will follow the carrier and stall the rifle for subsequent shots. Functionally, a drop which dislodges the trigger to have slipped the sear will also have dislodged far enough to slip the safety block notch which you’re considering as a secondary sear. Quite literally, the “secondary sear” has to clear before the primary sear, else the secondary would risk catching the hammer as it breaks from the primary.

Wear to the primary sear is possible for any design - however, again, if the primary slips in a 2 stage (opposed to a fracture failure described above), it will have moved the trigger sufficiently far during the slip that the secondary notch would also be defeated. In that case, baby’s goin’ loud until it stops slipping or the mag is empty, as it will with any design which wears its way into a negative angle sear engagement.