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AR trigger assembly question

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https://sigforum.com/eve/forums/a/tpc/f/630601935/m/7480006854

July 05, 2019, 07:39 PM
PHPaul
AR trigger assembly question
So, I broke down and bought myself an EBR. A used DTI AR15 to be precise.

So far, I'm liking it a lot, but there's one rather odd problem: Every now and then (maybe once in 20 rounds) it will Fail to Fire on the first round in a magazine. The trigger pull feels the same and the sound of the hammer hitting the firing pin is the same, but no boom.

If I rack the bolt, ejecting the first round and feeding the second, it fires as normal and will empty the magazine without another misfire. The ejected round shows no strike on the primer and fires the next time it's chambered.

I'm inserting the magazine on a closed bolt, loading the first round by pulling back on the charging handle and letting the bolt drop via the spring and then thumping the forward assist with the heel of my hand.

I have noticed that the trigger pull is "soft" for lack of a better term but the let-off seems crisp. Trigger effort is noticeably less than my grandson's AR.

It's been thoroughly cleaned and lubed. I've cleaned probably 100 M-16's using the Navy 3M Maintenance Requirement Card (when I worked for Lockheed as a contract armorer) so I'm pretty confident in my methods for cleaning and lubing.

I'm thinking I might want to replace the hammer spring.

Anything else I should be looking at?



Be careful when following the masses. Sometimes the M is silent.
July 05, 2019, 08:00 PM
ARMT Guy
quote:
Originally posted by PHPaul:
So, I broke down and bought myself an EBR. A used DTI AR15 to be precise.

So far, I'm liking it a lot, but there's one rather odd problem: Every now and then (maybe once in 20 rounds) it will Fail to Fire on the first round in a magazine. The trigger pull feels the same and the sound of the hammer hitting the firing pin is the same, but no boom.

If I rack the bolt, ejecting the first round and feeding the second, it fires as normal and will empty the magazine without another misfire. The ejected round shows no strike on the primer and fires the next time it's chambered.

I'm inserting the magazine on a closed bolt, loading the first round by pulling back on the charging handle and letting the bolt drop via the spring and then thumping the forward assist with the heel of my hand.

I have noticed that the trigger pull is "soft" for lack of a better term but the let-off seems crisp. Trigger effort is noticeably less than my grandson's AR.

It's been thoroughly cleaned and lubed. I've cleaned probably 100 M-16's using the Navy 3M Maintenance Requirement Card (when I worked for Lockheed as a contract armorer) so I'm pretty confident in my methods for cleaning and lubing.

I'm thinking I might want to replace the hammer spring.

Anything else I should be looking at?



You're on the right course with replacing the hammer spring.

Check the firing pin tip, ( for damage ) and the flared base at the opposite end of the firing pin, ( for carbon build up ) too.

You mentioned that it was used. Bought from a friend? Bought from a gun shop? Curious about what's know about how well, ( or poorly ) the previous owner maintained and how much it was used.



"Also I heard the voice of the Lord saying who shall I send, and who will go for us? Then said I, here am I, send me."



July 05, 2019, 11:06 PM
LDD
Who put this AR together? It's used so there's another possible explanation for which the solution is cheaper than replacing the hammer spring.

I've seen people install the hammer spring in incorrectly, with the legs under the trigger pin, instead of on top of it. This will result in light primer strikes. In effect, the spring is not being compressed hard enough so it doesn't spring back with the same force and the hammer doesn't have enough kinetic energy when released, to cause a correct primer strike.
July 06, 2019, 05:17 AM
PHPaul


I believe it's installed correctly, yes?

Used from a dealer. Visual inspection of exterior, barrel, rifling and chamber didn't show anything indicating abuse or neglect.

It hadn't been cleaned before being put on the rack tho. Not disgustingly dirty, but a lot of carbon on the small end of the bolt and around the gas rings.



Pin appears to be okay.



Be careful when following the masses. Sometimes the M is silent.
July 06, 2019, 06:13 AM
Dwill104
The hammer spring is installed backwards in the photo above. The side legs need to come back from the underside of the spring, not the top, and the legs for the loop behind the hammer need to come from the front of the spring, not the rear.



July 06, 2019, 08:04 AM
PHPaul
Ah. I wondered about that.

Thanks VERY much!

EDIT: Fixed. According to the provided picture, they had the pin in backwards as well. Now I'm going to have to go test fire it. Darn... Razz



Be careful when following the masses. Sometimes the M is silent.
July 06, 2019, 11:19 AM
Dwill104
quote:
Originally posted by PHPaul:
Ah. I wondered about that.

Thanks VERY much!

EDIT: Fixed. According to the provided picture, they had the pin in backwards as well. Now I'm going to have to go test fire it. Darn... Razz


No problem. The side that the outer groove on the hammer pin goes on doesn’t really matter. The spring inside the hammer engages the groove in the middle of the hammer pin. Usually the hammer and trigger pins are the same and the outer groove(s) are for when the pin is used for the trigger pin.