What's a two-stage trigger?


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Blackbeard
August 6, 2007, 09:05 PM
As the proud owner of a new RRA carbine, I've noticed that the brochure and several posts mention its "two-stage match trigger". I was hoping someone could explain to this newbie what that is.

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hksw
August 6, 2007, 09:53 PM
The trigger has two portions that can be felt during its travel when being depressed. In both cases, the trigger is under pressure from a spring (first stage) and, depending on the trigger, the striker or sear and some times also a second spring (second stage).

The first stage usually has a much longer travel than the second stage. The first stage is normally called take-up (and some other synonyms) but should not be confused with slack. Slack is just loose play in the trigger that isn't seeing any pressure from a spring or any other forces. For some adjustable triggers, the pull weight can be adjusted as well as length of travel (pre-travel).

At the end of the first stage, you'll experience a definite stop. This is the beginning of the second stage. It works essentially like a single stage trigger from here on. What you normally would experience with a single stage is the same. There may be creep, there may be overtravel, etc. Normally, folks would usually adjust to remove as much creep as possible without compromising safety. Also, second stage pull weight (and for some adjustable triggers, overtravel) is adjusted to shooter preferences.

Taking-up the first stage and stopping at the second before sending the round is known as staging the trigger.

cracked butt
August 7, 2007, 12:32 AM
The reasoning behind a 2-stage trigger is that you get the safety of having a long heavier trigger pull on the first stage but still retain the advantage of a light crisp trigger break on the 2nd stage.

SaMx
August 7, 2007, 12:36 AM
the other guys have it right, you have a longer take up, then you can just go POP! and fire. Some people like them, some don't.

thegriz
August 7, 2007, 12:56 AM
I have a 2 stage trigger on my mauser. It's nice for long shots. You squeeze until you feel the 2nd stage. Then just the tiniest pressure and boom. There's less risk of moving your aimpoint when pulling the trigger. It's not so great for quick shots.

GunTech
August 7, 2007, 02:24 AM
Two stage it typical in semi-auto rifles - particularly with match triggers. You need enough engagement of the sear to prevent it from 'bumping off' as the bolt slams home. You can reduce the weight of the pull by streading it iover distance - just like a lever, the longer the moment arm, the less the weight.

As a compromise, you dived the weight of the pull over two stages. The long, first stage prepps the sear, so that a short, relatively crisp second stage releases the sear. The alternative is is to have a relatively heavy singe stage with a short pull, or a very long one with a lighter pull.

Caimlas
August 7, 2007, 03:27 AM
By my understanding, a traditional trigger (single stage) has a single tension all the way through the trigger pull, whether it's heavy or light. Examples would be the SKS platform (an example of a crappy trigger) or a 1911 (a much better trigger).

A two-stage trigger, on the other hand, has some loose take-up followed by a crisp break.

Caimlas
August 7, 2007, 03:30 AM
The reasoning behind a 2-stage trigger is that you get the safety of having a long heavier trigger pull on the first stage but still retain the advantage of a light crisp trigger break on the 2nd stage.

I think you're confusing double action/single action and single action with double stage and single stage... There is no added safety with a double stage trigger, as the first stage is usually lighter instead of heavier, as is the case with a DA/SA trigger.

taliv
August 7, 2007, 03:52 AM
i don't think it's for safety, but he's right about the first stage being heavier.

for example, the adjustment range on the geiselle is
* First Stage: 3.2 to 5 pounds (4 pounds nominal)
* Second Stage: 0.5 to 1.5 pounds

JohnBT
August 7, 2007, 08:52 AM
My RRA Tactical Entry (or is it Entry Tactical) has a long light first stage and a heavier clean & crisp second stage. I don't know how it's supposed to be, but it's a great trigger for my purposes.

IIRC, it measured about 2# for the first stage and 3.25# or 3.5# for the second. If I was at home I'd stick the Lyman guage on it again to be sure of the numbers.

John

GunTech
August 7, 2007, 09:59 AM
Caimlas,

Technically, to be a two stage trigger, both stages involve unloading the sear. What you describe is called 'slack' and is just a loose trigger. A Mauser K96 has a two stage trigger. If you look at the trigger, you will notice a 'lump' that changes the mechanical advantage so that the first part of take-up - the first stage - moves the trigger into a position close to disengage over a long, but relatively light pull. Once the leverage changes, the final pull has less leverage, but shorter travel.

As an analogy, imagine that we want to protect our castle by putting a boulder up on the hill overlooking the road in. We don't really want it right on the edge of the cliff, because then it might fall accidentally. So we put it back from the edge. But we need to get it right up to the edge if it looks like we might need it, so that with only a little effort is needed to push it over. So we keep a big lever near the boulder. In an emergency, the lever is used to ge the boulder into 'firing position' (first stage) so that with just a small push, the bould can be forced over the cliff (second stage).

I'm not sure if the above analogy works, but basically, you will always have a certain load on the sear. In the case of the above Mauser K98, you have to hold back the force of the striker. And you must do it with enough sear engagement that you can't accidentaly but the sear off. Let's say that this requires 12 pounds of total force. Utilizing levers, we can either spread that force over a long distance - a light long pull, or use a shorter distance and a heavier pull. The less movement of the trigger, typically the less change to effect aim. But a short pull would be a heavy one.

Or, if you are really clever, you divide the pull into two stages. In the first stage, you have a long pull that eliminated say 9 of the 12 pounds. At this point the leverage changes so you have less mechanical advantage. But you only have 3 pounds to overcome, so even thoug you have much less leverage (and thus les trigger movement) the total force requires is much less. A 12 pound trigger has become a 9 pounds plus 3 pounds, with the first part spread over a lot of movement, and the crtical last few pounds is short and crisp

Clear as mud?

GoRon
August 7, 2007, 10:31 AM
I always wondered why the RRA triggers were called two stage.

My RRA has a lighter pull or "take up" then you feel resistance with a clean break to fire.

Actually the Chip McCormick on my other AR is the same. Lighter take up with a definite point where more pressure induces a clean break and boom.

The single stage RRA I have has no take up and a heaver trigger pull. There is also some creep before it breaks. Same thing with my buddies single stage Bushmaster.

Father Knows Best
August 7, 2007, 11:00 AM
GunTech, that's the best explanation of a two stage trigger I have ever seen.

BigG
August 7, 2007, 11:23 AM
I personally do not see any advantage from the point of the shooter for a two stage trigger. I also do not agree that there is a leverage difference that distinguishes the two stage trigger. Some may have it but it generally just means a long initial take up and then you get to the "real" trigger pull that releases the striker.

I do see that management of an army of ill trained people going around with their fingers on the trigger might make for less negligent discharges. The 2 stage trigger goes back to the old military triggers like on the German Mauser. You can use the gun under all conditions - in freezing weather, with gloves on, whenever. You have to make a conscious effort to pull the trigger far enough to make the gun discharge. At least, that is my reasoning.

The SIG automatics have a two stage trigger, long take up and then you get to the "real" trigger pull. YMMV

Mr White
August 7, 2007, 11:35 AM
There is a huge advantage to having a 2 stage trigger for competition shooting.

NRA rules state that a service rifle trigger can have no less than 4.5# of pull. A single stage 4.5# trigger would be heavy enough to effect accuracy, but if you set your takeup stage to 4#, and your break stage to .5#, you squeeze the takeup until it stops. Once you get used to your trigger, this becomes very easy to feel. Then, once you're settled and exhaled and your sight picture is what you want, and you're against the 2nd stage, that last little squeeze fires the shot. There's no movement of the gun, and hardly any effort is needed to squeeze that last .5# when you're already squeezing 4# on the takeup.

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