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3/28/2013 10:38:23 AM EDT
So, last night, my father-in-law and I went to fire our creation for the first time.

Creation:
Thunderstreak M4 16" Mil-spec Upper
Seekins lower with DPMS LPK
Standard Magpul Stock with buffer.
Standard Magpul magazine

the Rounds, New 5.56 NATO 62gr

So, when you pull the trigger, it fires off 2 rounds.  

Thoughts?

Thanks!
3/28/2013 10:42:23 AM EDT
[#1]
Quoted:
So, last night, my father-in-law and I went to fire our creation for the first time.

Creation:
Thunderstreak M4 16" Mil-spec Upper
Seekins lower with DPMS LPK
Standard Magpul Stock with buffer.
Standard Magpul magazine

the Rounds, New 5.56 NATO 62gr

So, when you pull the trigger, it fires off 2 rounds.  

Thoughts?

Thanks!


Do you have another trigger to drop in?

3/28/2013 10:44:03 AM EDT
[#2]
Quoted:
Quoted:
So, last night, my father-in-law and I went to fire our creation for the first time.

Creation:
Thunderstreak M4 16" Mil-spec Upper
Seekins lower with DPMS LPK
Standard Magpul Stock with buffer.
Standard Magpul magazine

the Rounds, New 5.56 NATO 62gr

So, when you pull the trigger, it fires off 2 rounds.  

Thoughts?

Thanks!


Do you have another trigger to drop in?



Nope
3/28/2013 10:45:45 AM EDT
[#3]
Did you do a function check prior to firing?

Did you install the disconnector spring correctly (fat side down)?
Did you use the correct disconnector spring (not confuse it with the bolt catch spring)?
Did the trigger pin actually pass through the pin hole in the disconnector?
Did you install the trigger spring and/or hammer spring upside down?
Are the sear surfaces on the trigger, hammer and disconnector sharp and square?
Does it only double when you release reaward pressure on the trigger or when you keep holding back on the trigger during cycling?
3/28/2013 10:58:35 AM EDT
[#4]
Quoted:
Did you do a function check prior to firing?

1.Did you install the disconnector spring correctly (fat side down)?
2.Did you use the correct disconnector spring (not confuse it with the bolt catch spring)?
3.Did the trigger pin actually pass through the pin hole in the disconnector?
4.Did you install the trigger spring and/or hammer spring upside down?
5.Are the sear surfaces on the trigger, hammer and disconnector sharp and square?
6.Does it only double when you release reaward pressure on the trigger or when you keep holding back on the trigger during cycling?


Did you do a function check prior to firing? - I am assuming that you mean, did you try it out the trigger before adding live ammo.  Yes, though I didn't try pressing back on the hammer with the trigger pressed.

1. Yes, I checked that myself
2. Yes, I remember that the sorting them out.
3. Yes
4. will have to check, but am fairly certain we did it correct.  We folllowed the pictures off the ar15.com website.
5. yes, they were polished.
6. Since I wasn't the one firing, I did ask.  He said he pulled the trigger to fire, but didn't pull after it disengaged the hammer nor did he release the trigger.

Thanks for the help,
3/28/2013 11:35:20 AM EDT
[#5]
Did it cycle after the second shot and chamber a third round?  If so it's strange that it would stop firing after two rounds
3/28/2013 11:47:12 AM EDT
[#6]
Quoted:
Did it cycle after the second shot and chamber a third round?  If so it's strange that it would stop firing after two rounds


Yes, it was ready for the 3rd round.

Next time we go out, I am going to bring my lower, and my buddy's lower and see if there is a difference.

I agree it is strange... hence why I asked here.
3/28/2013 11:53:48 AM EDT
[#7]
Quoted:
Quoted:
Did you do a function check prior to firing?

1.Did you install the disconnector spring correctly (fat side down)?
2.Did you use the correct disconnector spring (not confuse it with the bolt catch spring)?
3.Did the trigger pin actually pass through the pin hole in the disconnector?
4.Did you install the trigger spring and/or hammer spring upside down?
5.Are the sear surfaces on the trigger, hammer and disconnector sharp and square?
6.Does it only double when you release reaward pressure on the trigger or when you keep holding back on the trigger during cycling?


Did you do a function check prior to firing? - I am assuming that you mean, did you try it out the trigger before adding live ammo.  Yes, though I didn't try pressing back on the hammer with the trigger pressed.

1. Yes, I checked that myself
2. Yes, I remember that the sorting them out.
3. Yes
4. will have to check, but am fairly certain we did it correct.  We folllowed the pictures off the ar15.com website.
5. yes, they were polished.
6. Since I wasn't the one firing, I did ask.  He said he pulled the trigger to fire, but didn't pull after it disengaged the hammer nor did he release the trigger.

Thanks for the help,



Function Check
3/28/2013 11:56:51 AM EDT
[#8]
Quoted:
Quoted:
Quoted:
Did you do a function check prior to firing?

1.Did you install the disconnector spring correctly (fat side down)?
2.Did you use the correct disconnector spring (not confuse it with the bolt catch spring)?
3.Did the trigger pin actually pass through the pin hole in the disconnector?
4.Did you install the trigger spring and/or hammer spring upside down?
5.Are the sear surfaces on the trigger, hammer and disconnector sharp and square?
6.Does it only double when you release reaward pressure on the trigger or when you keep holding back on the trigger during cycling?


Did you do a function check prior to firing? - I am assuming that you mean, did you try it out the trigger before adding live ammo.  Yes, though I didn't try pressing back on the hammer with the trigger pressed.

1. Yes, I checked that myself
2. Yes, I remember that the sorting them out.
3. Yes
4. will have to check, but am fairly certain we did it correct.  We folllowed the pictures off the ar15.com website.
5. yes, they were polished.
6. Since I wasn't the one firing, I did ask.  He said he pulled the trigger to fire, but didn't pull after it disengaged the hammer nor did he release the trigger.

Thanks for the help,



Function Check


Ahh, yes it passed the function test.
3/28/2013 12:04:38 PM EDT
[#9]
Quoted:
Quoted:
Did it cycle after the second shot and chamber a third round?  If so it's strange that it would stop firing after two rounds


Yes, it was ready for the 3rd round.

Next time we go out, I am going to bring my lower, and my buddy's lower and see if there is a difference.

I agree it is strange... hence why I asked here.


It sounds like this is what is happening:

Pull trigger, fire a round and action cycles, loading a new round.
Release trigger, hammer is not caught and fires a round, the action cycles and loads a new round.
It stops firing until the trigger is puleld again and the cycle repeats.
The recoil from the first round combined with relaxing the trigger finger slightly could make it appear that it is firing double, when it is actually firing the second round when the trigger is released.
A proper function check will determine if this is what is happening.

If that is the case you have either a bad disconnector or the disconnector hook on the hammer is wrong.
look for burrs on the sear surfaces, especially the disconenctor which can somethimes be a poorly machined part.
An outside chance the lower is out of spec and the distance between the trigger and hammer pin holes are just off enough to affect the sear engagement geometry.

My first AR did this and it was a bad disconnector (stamped not machined) combined with cheap internals (the sear surfaces on the trigger and hammer were actually chipping).
I have used DPMS LPKs with no problems, so I don't suspect they are as bad as I describe above, but a bad part can get through.
3/28/2013 12:06:28 PM EDT
[#10]
Quoted:


Ahh, yes it passed the function test.


You are absolutely sure that after you pull the trigger, the hammer falls, you continue backward pressure on the trigger and cycle the action, when you let the trigger return forward that the hammer does not fall?
3/28/2013 12:15:19 PM EDT
[#11]
Quoted:
Quoted:


Ahh, yes it passed the function test.


You are absolutely sure that after you pull the trigger, the hammer falls, you continue backward pressure on the trigger and cycle the action, when you let the trigger return forward that the hammer does not fall?


I will check tonight

Thanks!
3/28/2013 9:33:42 PM EDT
[#12]
backwards spring. maybe
3/28/2013 10:08:56 PM EDT
[#13]
Also,

If you are going to a range there will most likely be someone there that can help out too...

Nothing with the op...but, 75% or more people do not perform the function checks properly...especially new to the platform...reading how to perform one is like learning to fly an airplane from nothing but a book..There is a lot of feel involved...

Someone that runs ar's quite often can usually spot or feel the issue in less than 10 seconds...and 9 of thors seconds is clearing the rifle...

Yes, find a vet let them examine it and they will know what it is in a jiffy...

Bret
3/29/2013 8:04:58 AM EDT
[#14]
Quoted:
Also,

If you are going to a range there will most likely be someone there that can help out too...

Nothing with the op...but, 75% or more people do not perform the function checks properly...especially new to the platform...reading how to perform one is like learning to fly an airplane from nothing but a book..There is a lot of feel involved...

Someone that runs ar's quite often can usually spot or feel the issue in less than 10 seconds...and 9 of thors seconds is clearing the rifle...

Yes, find a vet let them examine it and they will know what it is in a jiffy...

Bret


Good idea, my FFL guy should know.. IE has more experience than me.

TY!
3/29/2013 10:02:35 AM EDT
[#15]
Maybe the disconnector spring is in backwards? The larger end should be flush against the slot in the trigger, sometimes it has a hard time fitting. The spring could be backwards thus causing it to bind and not function properly.
3/29/2013 10:20:35 AM EDT
[#16]
I had a friend that was getting double taps at the range with a new trigger.  He had to bring it back to his smith to continue tuning the trigger to get it to stop.  Not sure what was being worked on by the smith.  I guess the faces of trigger, disconnector.
First and foremost, you received the function check wisdom already.

Let's assume you discover that the function is not working correctly.  What do you do at that point?
Do you start with checking the spring configuration then go to the disconnector surface?
3/29/2013 10:33:39 AM EDT
[#17]
Quoted:
Maybe the disconnector spring is in backwards? The larger end should be flush against the slot in the trigger, sometimes it has a hard time fitting. The spring could be backwards thus causing it to bind and not function properly.


I remember putting the big side down.. and yes.. it was a bit of a bugger.
3/29/2013 10:56:12 AM EDT
[#18]
call dpms they will overnight you a new fcg  and a return ups label. they want that back   asap. trust me
3/29/2013 10:57:23 AM EDT
[#19]
Quoted:
I had a friend that was getting double taps at the range with a new trigger.  He had to bring it back to his smith to continue tuning the trigger to get it to stop.  Not sure what was being worked on by the smith.  I guess the faces of trigger, disconnector.
First and foremost, you received the function check wisdom already.

Let's assume you discover that the function is not working correctly. What do you do at that point?
Do you start with checking the spring configuration then go to the disconnector surface?


Yes,
I put the elements in my first post in a specifc order.
Always check for the simplest thing first.
In this case ensure the parts are installed correctly before assuming the parts themselves are at fault.
Then look at the internal parts before suspecting the lower itself is out of spec.
3/29/2013 6:52:59 PM EDT
[#20]
It's funny that this came up, cause I was at the range today and had my 22lr ar double fire, but I think it was caused by the ammo.
3/29/2013 8:12:49 PM EDT
[#21]
Rule number one... Double tap... ;)
4/4/2013 7:00:27 AM EDT
[#22]
Quoted:
Quoted:
Maybe the disconnector spring is in backwards? The larger end should be flush against the slot in the trigger, sometimes it has a hard time fitting. The spring could be backwards thus causing it to bind and not function properly.


I remember putting the big side down.. and yes.. it was a bit of a bugger.


SOLUTION

Well, we found out that the disconnecter was sticking in the trigger.  My FFL guy had another and it worked fine.

Thank you all for helping out.  looking at the spring helped find the problem.
4/4/2013 9:19:43 AM EDT
[#23]
good deal, glad you got it fixed
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