Typical AR sear engagement?

[boing]

My Bushmaster carbine has a lousy trigger, with severe creep. I can feel the trigger slip substantially before the hammer falls, which ruins any deliberate trigger pull for a precise shot. The wear on the trigger surface indicates about 0.075" of sear engagement. That seems like a lot, but I don't know what's normal for a basic AR.

I don't want a "match grade" trigger in this gun. I want rugged & reliable "mil-spec" parts, if a reasonable trigger pull can be had using them (preferably without having a gunsmith work-over the existing parts.)

I have a RRA match trigger in my A1 clone, and while it's a fine trigger for target/plinking, it already seems to be going a little quirky (reset failures), and it's hardly been shot. I want reliability first in my carbine, and I'm wondering if a simple trigger swap might bring the trigger pull up to par? The wear on the hammer surface seems relatively even, so I think the problem lies mainly with the trigger.

 

[Chris Rhines]

I don't want a "match grade" trigger in this gun. I want rugged & reliable "mil-spec" parts, if a reasonable trigger pull can be had using them (preferably without having a gunsmith work-over the existing parts.)

The creep and roughness in your trigger are caused by a combination of factors:
- fine lateral serrations in the hammer and trigger engagement surfaces.
- an excessive amount of hammer/sear engagement (75 thou is way, way too much engagement, though typical for ARs. A safe and reasonable engagement would be 0.025")
- The angle of engagement between the hammer and sear face is strongly positive.

Swapping parts will not necessarily correct all or any of those problems. You might be able to get a better trigger pull by swapping your trigger parts for other Mil-Spec components, but the odds are against you.

Your choices are either have a match trigger fitted to your rifle, have the existing parts worked over by someone competent (or do it yourself), or learn to live with the trigger as it is.

- Chris

 

[HSMITH]

I had the same thing in mine. I cut the engagement to 20 thou, dropped the positive angle to nearly nuetral and cleaned up the engagement surfaces, it made a WORLD of difference. I went from a 9-13 pound trigger pull depending on which time you pulled it, to a consistent 4 1/4 pound pull.

One part worries me, I don't have ANY facts and this is just my SWAG at what is what so bear that in mind, I am worried that the sear isn't through hardened. I think that it is case hardened, and if it is the soft metal is exposed and could cause a durability issue over the course of a couple thousand shots. If I see evidence of this I am out a couple bucks for a new sear, no biggie. At least the rifle is shootable now.

 

[BigG]

To my knowledge, there is no sear on an AR15 unless you have the fun version, then that is called an autosear. The trigger just mates up with a notch on the hammer. I think if you try to clean up the engagement you will end up with a ruined trigger of hammer shortly as the surface hardening will be removed. Another reason to buy a Colt, imho. They usually have good triggers to begin with. JMTC YMMV etc.

 

[boing]

Yes, the parts are only surface hardened. How deep the hardening goes, I don't know, but I don't want to take off 0.055" from the sear surface or hammer hook. I doubt the useable area of hardness goes anywhere near that deep.

No, there is no "sear" as such, but for the sake of conversational convenience, the engagement area of the trigger is referred to as the sear, as it serves the same function. If it has an official name other than "The Forward End of the Trigger that Engages The Hammer and Acts as a Sear", then I'd be glad to propagate it's correct usage throughout the internet.

 

[BigG]

Whatsit called?

Damfino - as Art would say. I would call it the hammer notch and the trigger nose but what do I know?

 

[swingset]

You can do wonders with just stoning the surfaces, hitting them with jeweler's rouge, and switching to a lighter hammer spring.

My trigger is not a match trigger, but it's waaaay better than stock, and it's reliable even with hard mil. primers.

 

[1911 guy]

Colt triggers

When I bought my most recent lower the gunshop guru tried to pawn a Colt off on me. The trigger was as bad or worse than any I've shot. So, I handed it back to him and asked him to order me a DPMS for half the price.
That said, the AR platform does not lend itself to phenominal triggers no matter what make.

 

[BigG]

I don't know what you call phenomenal triggers but the standard Colt trigger is just fine for me. Better than most military triggers and equal to most civilians. If you are talking about a 2 ounce let off, I guess no it's not "phenomenal" but it's phenomenal enough for me.

 

[Rockstar]

BigG: What's the pull weight of your Colt trigger? What kind of trigger pull gauge do you use?

To the guys recommending stoning; "What part of 'case hardened' don't you understand?"

 

[Raygun]

That said, the AR platform does not lend itself to phenominal triggers no matter what make.

Ever tried a Jewell trigger? I think I might classify it as phenomenal, as far as AR triggers go. Of course, the words "inexpensive" and "phenomenal" don't tend to go together. When I scrape up the dough, I'll be putting one in mine.

In the mean time, in order to deal with the excessively heavy (@ 12 lbs) and creepy pull (not sure exactly how long, but it was too long. not an AK trigger, but not much better) of a stock DPMS trigger, I filed down the hammer hook by a very small amount, polished up and dabbed a little tetra grease on the engagement surfaces. The trigger now has much less creep (probably less than 1/16th; whatever it is, it's enough to keep it from letting off when the safety is on) and it breaks very cleanly at 5 3/4 lbs. It's no target trigger, but it's just about perfect for a working man, IMO.

EDIT: Got home to test it. My worked-on trigger shows 0.055" of creep and an average of 10 pulls shows it breaking at 5.9 lbs. Anyway, it's one hell of an improvement over the stock trigger.

 

[swingset]

To the guys recommending stoning; "What part of 'case hardened' don't you understand?"

Stoning doesn't mean using a 100 grit whetstone.

A fine 1200 grit arkansas stone will only polish, it won't go through the case hardening, not even close.

If you're worried, use nothing but Jeweler's rouge on a buffing wheel and go slow. You will only remove the serrations that cause creep, not any hardening.

 

[BigG]

If you're worried, use nothing but Jeweler's rouge on a buffing wheel and go slow. You will only remove the serrations that cause creep, not any hardening.

I may have been born at night, but it wasn't last night. If you remove serrations, you remove the surface hardening. It's on the SURFACE.

 

[Derby FALs]

15-Minute Practical Trigger Job for the AR-15

 

[HSMITH]

BigG, the case hardening is at least a couple thousandths deep, light stoning won't compromise it.


My hammer and sear were Colt, and they were HORRIBLE.

 

[wanderinwalker]

The only AR triggers I have found usable out of the box have been on match rifles. Fortunately, the ones I have found unsuitable have been on other people's rifles; therefore, not my problem!

Polishing the engagement surfaces and maybe swapping for a lighter hammer spring seem to be the best ways of alleviating issues with the stock triggers. No matter who made the rifle, a box-stock AR usually needs a little TLC on the trigger group, IMO. My father has an old Colt SP-1, that you can cock the rifle, disengage the safety and literally hang the thing by the trigger shoe. It won't trip from the weight of the rifle! Ball-park guess is 8-9 pound trigger mash.

 

[Rockstar]

I've done a little polishing on the mentiioned surfaces, with excellent results. Glad that the stoning method was clarified.

 

[1911 guy]

Case hardening

Being a machinist and having done a little heat treating myself, stoning the surface will absolutely NOT take away any hardness if you deburr/stone the surface. Case hardening is done based on material type and thickness, burrs not being accounted for. The case depth will be consistent and the burrs will be somewhat harder than the finished piece due to small area of material and less conduction to the thicker parts of the metal. Stone these off and you wind up with what the factory should have given you in the first place.

 

[Gordon]

"I may have been born at night, but it wasn't last night. If you remove serrations, you remove the surface hardening. It's on the SURFACE."
I too worried about this, I wouldnt put an aftermarket trigger on my Colt AR tactical carbines. So AFTER I stoned and polished the surfaces , put in lighter springs (Wolfe), I had the polished parts Industrial Flash Hard Chromed, Then I buffed them on rouge wheel to a mirror. TW 25 grease and you have a 4 pound crisp trigger that should NEVER go down!

 

[Raygun]

Out of curiosity (and having a spare hammer spring), I followed the instructions in the link posted by Derby FALs regarding the hammer spring modification. It dropped the trigger pull weight down to a very consistent 4.25 lbs.

Thanks, Derby FALs!