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View Full Version : My First AR Build-----Does'nt work!


New2guns
09-27-2010, 11:16 PM
Thought I would troll for some tips. I bought this lower to justify paying another DROS fee. I no longer buy rifles one at a time, too expensive.
Anyway built this Aeroprecision lower and put an M4 16" upper on it. Everything functions as expected. Four types of mags tried same result.
I think it might be refered to as a "short stroking" but not sure. I am truely new to guns.
scenario:
load, charge, fire. Second trigger pull nada.
Charge, fire, trigger pull, nada
Charge, fire 2 rounds out one pull
charge, fire, trigger pull nada
Charge, fire, trigger pull, nada
Charge, fire 3 rounds out one pull.

I weighed the buffer tube compared to my friends same weight. Same spring length. Stripped the bolt, cleaned piston rings etc and it opperates smoother but have not taken it to check it out yet.
!. Why would it "short stroke"? Gas block plugged?
2. Why would it fire three rounds with one pull? (definately not bump fired):confused:

The hammer is not notched as is my Ruger.
Just looking for some ideas so I can check them out on the next shooting trip.
All parts are brand new. Using a M4 heavy barrel still direct impingment

Thanks

U5512
09-27-2010, 11:22 PM
Have you tried different magazines?

SixPointEight
09-27-2010, 11:22 PM
Did you install the lpk or buy it assembled? Recheck the fcg springs, it's a common cause of doubles from what I hear.

Have you tried different magazines?

You sir...are a failure.

bjl333
09-27-2010, 11:23 PM
new or used upper ??

bjl333
09-27-2010, 11:24 PM
new or used upper ??

sounds like the gas is not going back to cycle the bolt.

EDIT: not a gas issue. trigger group issue.

SixPointEight
09-27-2010, 11:26 PM
sounds like the gas is not going back to cycle the bolt.

It sounds a bit like a short stroke, but why the doubling then?

OP the rounds that ejected when you racked it, were they fired cases or unfired rounds?

bjl333
09-27-2010, 11:28 PM
It sounds a bit like a short stroke, but why the doubling then?

OP the rounds that ejected when you racked it, were they fired cases or unfired rounds?

something in the fire control group... get someone to look at it.

New2guns
09-27-2010, 11:35 PM
something in the fire control group... get someone to look at it.

This sounds to be the case, I will go through it again. I used the AR15.com assemble sheet.

JT1989, No rounds chambered on the short stroke so nothing ejected

SixPointEight
09-27-2010, 11:37 PM
So it's cycling enough to eject but not chamber. When it does chamber it doubles?

Ammo type?

bjl333
09-27-2010, 11:40 PM
So it's cycling enough to eject but not chamber. When it does chamber it doubles?

Ammo type?

The hammer could be partly loose and hanging up the bolt, or freeing the bolt for the doubling/tripling.

bjl333
09-27-2010, 11:41 PM
hahaha ... JT, N2g got you bugged now. Just go over and tear his AR apart !!! :eek:

SixPointEight
09-27-2010, 11:46 PM
hahaha ... JT, N2g got you bugged now. Just go over and tear his AR apart !!! :eek:
I just realized he's in Sac too lol

New2guns
09-27-2010, 11:47 PM
So it's cycling enough to eject but not chamber. When it does chamber it doubles?

Ammo type?

Ammo is annealed case brass and ball with green coded primers staked (MKE 04)

The times it did chamber a new cartridge it fired it

SixPointEight
09-27-2010, 11:52 PM
Ammo is annealed case brass and ball with green coded primers staked (MKE 04)

The times it did chamber a new cartridge it fired it

I'm down to a WAG. So my stab at it is two things combined. The ammo sounds like it's milsurp, so shouldn't be underpowered. Could be too heavy of a buffer, but it sounds like it's a regular carbine buffer.

Could be underlubed causing the short stroke, and a spring installed wrong to cause the doubling.

stphnman20
09-27-2010, 11:55 PM
I think you installed the hammer/spring backwards.

New2guns
09-27-2010, 11:55 PM
The hammer could be partly loose and hanging up the bolt, or freeing the bolt for the doubling/tripling.

OK I just tried it while holding the trigger and the hammer will follow the bolt back if holding the trigger. So I must have something assembled wrong. The sear should lock the hammer even with the trigger held. Right/

stphnman20
09-27-2010, 11:57 PM
Ammo is annealed case brass and ball with green coded primers staked (MKE 04)

The times it did chamber a new cartridge it fired it
Yup sound like your hammer spring is backwards.

SixPointEight
09-27-2010, 11:57 PM
OK I just tried it while holding the trigger and the hammer will follow the bolt back if holding the trigger. So I must have something assembled wrong. The sear should lock the hammer even with the trigger held. Right/

Yes it absolutely should. Another poster mentioned the hammer spring being backwards. Common, and known to cause doubling.

Fix the spring, then we'll work on the short stroking

New2guns
09-27-2010, 11:57 PM
It is past my bedtime so I will redo this tomorrow and follow up.
Thanks you guys.
Jim

SJgunguy24
09-28-2010, 12:02 AM
I think you installed the hammer/spring backwards.

100% this is your answer. If the gun was short stroking there would be no follow up shot at all. The BCG would not travel enough to strip the next round.

New2guns
09-28-2010, 9:33 PM
100% this is your answer. If the gun was short stroking there would be no follow up shot at all. The BCG would not travel enough to strip the next round.

Took my two AR's and placed them side by side to compare.
The Aeroprecision and generic LPK were assembled correctly by comparing the Ruger SR556 lower to it. Hammers are slightly different but assembly matches exactly. They were both function tested the same and react exactly the same so AR15.com instructions seem to be correct. SR556 buffer spring is about one inch longer than the TAPCO buffer spring weights are basiclly only a gram difference. I have two more rifles to assemble so when they get here I will compare parts. It hasn't been fired sine I cleaned the piston rings on the brand new bolt but since doing so the bolt opperates much smoother. So will have to wait and see.
I am converting this rifle to gas piston but want to verify the operation in normal mode before doing so.
This may be just simply a new phenomenon rather than an anomaly. It is just such a pain in the arse to go shoot since the closet range is 35 miles away.
Anyway, thanks for the suggestions.

drs2714
09-28-2010, 9:41 PM
Check your disconnector/spring?

Jerkdog
09-28-2010, 9:57 PM
Where in Sac are you? Call Sacramento Black Rifle in Rocklin and ask if you can bring in your lower to have them double check the LPK install (I'd leave the upper at home). Buy a couple of Pmags for their trouble.

Also check for uneven wear inside the buffer tube - the buffer or spring could be hanging up on something, or the buffer tube could be slightly out of spec.

If you have access to another upper - swap that with the upper you're running right now. If the same prob's come up, you know it's something with your lower for sure. Good luck.

saber
09-28-2010, 10:01 PM
I have had that exact same issue and it was a disconnector spring upside down. You have to completely take the trigger group apart to see if it is installed correctly.

Google upside down disconnector spring and you will a ton of posts about it.

New2guns
09-28-2010, 10:19 PM
I have had that exact same issue and it was a disconnector spring upside down. You have to completely take the trigger group apart to see if it is installed correctly.

Google upside down disconnector spring and you will a ton of posts about it.

Thanks you guys, I will check this out.

dieselpower
09-28-2010, 10:29 PM
wow it took 22 post to say disconnector spring...you guys are slipping.

#1 cause of double taps on a newly assembled lower = upside down disconnecter spring. The fat end goes into the trigger troth.

New2guns
09-28-2010, 11:16 PM
OK you guys, don't laugh at me on this thing. This is my first build. I dissasembled it to find NO disconnect spring. I have since found it and installed it and seems to function test good. I was lucky to have saved the mag button and spring as that is where I found the disconnect spring. All fixed.
Thank you so much for all the help and guidence. You guys rock

NorCalRedneck
09-29-2010, 1:12 AM
Thanks for this post. I just happened to be reading this after I assembled my first lower and it clicked in my head that I put that spring in backwards. Just took it apart and fixed it in no time.

keson
09-29-2010, 1:25 AM
Glad you fixed the problem yourself :)

JTROKS
09-29-2010, 7:38 AM
OK you guys, don't laugh at me on this thing. This is my first build. I dissasembled it to find NO disconnect spring. I have since found it and installed it and seems to function test good. I was lucky to have saved the mag button and spring as that is where I found the disconnect spring. All fixed.
Thank you so much for all the help and guidence. You guys rock

Thanks for this post. I just happened to be reading this after I assembled my first lower and it clicked in my head that I put that spring in backwards. Just took it apart and fixed it in no time.

:)








:D:D









:rofl2::rofl2::rofl2:





I remember back in the mid 90s when I assembled my second lower I did the same thing.

Wherryj
09-29-2010, 9:03 AM
Courtesy of M4carbine.net.

http://i759.photobucket.com/albums/xx238/wherryj/AR15-HammerSpringInstall.jpg

dfletcher
09-29-2010, 9:11 AM
OK you guys, don't laugh at me on this thing. This is my first build. I dissasembled it to find NO disconnect spring. I have since found it and installed it and seems to function test good. I was lucky to have saved the mag button and spring as that is where I found the disconnect spring. All fixed.
Thank you so much for all the help and guidence. You guys rock

Just FYI - the disconnector spring and bolt hold open spring look quite a bit alike. The BHO spring is a consistent diameter coil top to bottom while the disconnector spring is slightly pyramid shaped. Most manufacturers color a coil or two on the diconnector spring and it seats inside the trigger wide end down.

If you happened to put the disconnector spring inside the BHO hole and it works I'd just leave it there and buy another one for the disconnector, no sense pounding out the pin if it works.

Rogu3
09-29-2010, 9:19 AM
random thought...firing pin issues?

hypnoman
09-29-2010, 10:15 AM
OK you guys, don't laugh at me on this thing. This is my first build. I dissasembled it to find NO disconnect spring. I have since found it and installed it and seems to function test good. I was lucky to have saved the mag button and spring as that is where I found the disconnect spring. All fixed.
Thank you so much for all the help and guidence. You guys rock

I will do my first build (hopefully) soon . . . and I am glad to read this!!

I will approach it cautiously and remember the pain others have suffered along this path and respect the lessons your learned . . .

Omega13device
09-29-2010, 4:10 PM
Don't forget to lube the BCG. A wet AR is a happy AR.

vta
09-29-2010, 4:19 PM
disconnector spring is exactly what I was thinking all along. It's easy to forget that if you are not paying attention while assemblying the fcg.

goober
09-29-2010, 4:28 PM
Check your disconnector/spring?

I have had that exact same issue and it was a disconnector spring upside down. You have to completely take the trigger group apart to see if it is installed correctly.

Google upside down disconnector spring and you will a ton of posts about it.

Thanks you guys, I will check this out.

wow it took 22 post to say disconnector spring...you guys are slipping.

#1 cause of double taps on a newly assembled lower = upside down disconnecter spring. The fat end goes into the trigger troth.

OK you guys, don't laugh at me on this thing. This is my first build. I dissasembled it to find NO disconnect spring. I have since found it and installed it and seems to function test good. I was lucky to have saved the mag button and spring as that is where I found the disconnect spring. All fixed.
Thank you so much for all the help and guidence. You guys rock

lol :rolleyes:
good for drs2714 & saber for FINALLY throwing out the correct diagnosis.
as dieselpower noted, this was the OBVIOUS place to look first.
sheez. :rolleyes:
anyway, glad the OP got his AR sorted.

bearj
09-29-2010, 6:03 PM
wow, no spring, this is why i will never buy a used gun! lol

xibunkrlilkidsx
09-29-2010, 6:20 PM
Don't forget to lube the BCG. A wet AR is a happy AR.

giggity.


such simple steps sometimes. Uusally having spare aprts when your done is a bad clue that something is a miss.

Shady
09-29-2010, 6:25 PM
it refuses to fire because you keep calling it a build