AR15 Problem

[BigJon]

My AR is locking up during cycling when the bolt gets 1/2 of the way back to battery. In summary, if I hold the trigger rearward and cycle the bolt, the bolt stops on something 1/2 of theh way back to battery. It has to be some kind of mechanical interference among parts because it occures whether I'm live firing or dry firing the rifle. Here's a breakdown of the sequence of events:

During Live Fire:
1. Fire rifle.
2. Bolt goes back and eject the emptyy.
3. Bolt starts back forward, starts another round out of the mag, but then stops half way to battery. (I am still holding trigger back at this time.)

The problem occurred during live fire, and initially I thought I had a feeding issue, until the same thing happened during dry fire.

During Dry Fire:
1. Rifle unloaded, in battery, and cocked.
2. Pull the trigger, and the rifle dry-fires.
3. Without releasing the trigger, grab the charging handle, fully retract the bolt, and then let it go forward.
4. Without releasing the trigger, start allowing the bolt to go back forward.
5. Bolt goes half way home but stops half way to battery.
6. Release the charging handle.
7. Release the trigger. Bolt staysy put.
8. Grab the charging handle again and slightly retract the bolt.
9. Bolt now free to go all the way home.

This is not an intermittent problem; if I hold the trigger back and cycle the action, whether by live fire or dry fire, the bolt will lock up as described every time. Would appreciate any guidance you could give me on what's wrong.

Best,
Jon

 

[taliv]

sounds like your disconnector is jacked up.

i'm guessing if you look at your hammer, there is a little notch in the top of the face (the part that hits the firing pin)

and i'm guessing your bolt carrier doesn't have what is known as a firing pin shroud. in other words, if you look at your bolt carrier group from the bottom, you can see the last half inch or so of the firing pin

my speculation is that the flat part on the end of the firing pin is catching in the notch on the hammer as it was designed to do. otherwise, the hammer would follow the carrier as it went forward and empty your magazine in full-auto

you need to take the rifle to a qualified gunsmith and get them to fix it. if you don't have a gunsmith, you could try replacing the entire FCG

 

[LJH]

please clarify "half way", does this mean the bolt has not gotten to the barrel as in you can see the bolt face? Or half way as the bolt has touched the barrel but did not lock up?

 

[BigJon]

The former. If one looks into the port when the rifle is locked up, he'll see the front edge of bolt right in the middle of the port. In other words, in the rear half of the port you see bolt, and in the forward half of the port you see air.

 

[BigJon]

Oh, and taliv is correct: no shroud.

 

[BBBBill]

Howdy, Jon. Good to see you over here, too. Form the sound of it, TALIV has got it pegged. Do you have a stock AR trigger group? Has it been "tuned?" Is it Colt or some other known good brand?

 

[taliv]

btw, i went to high school at Jefferson Davis back in the 80s

been a long time since i was in montgomery

 

[BigJon]

Hi, BBBBill. Glad to be here. Been a member here for quite awhile, but haven't posted much because my "hobbies" got so weapon-specific if you know whata mean. . I did replace the trigger group a long time ago, but I cannot remember whose parts I used. I am 100% certain that I used good quality parts, though, because I always do no matter what I'm working on. Someone once said something that has always stuck with me - "Buy cheap, buy twice." I think, but am not certain, that the group may have been McCormick, but again, it's been so long that I just don't remember. As far a "tuning" goes, if it has been tuned, it has been only been tuned unwittingly by my inept manipulations of it.

taliv - JD, huh? Wow! Small world! C'mon back - Montgomery has really gotten progressive over the last 20 years - we actually have crepe myrtles planted in the median of the Interstate now!

Best,
Jon

 

[BigJon]

Aha! More memory is starting to return. I now remember the REASON I changed the fire-control group. The rifle was double-tapping. That was years ago.

With the rifle's history being one full of alterations, and with the upper and lower being from different manufacturers, I am getting the feeling that the best (most practical) move is for me to send it to a qualified AR 'smith (which obviously I certainly am not).

Best,
Jon

 

[taliv]

well, like i said, you can try swapping out parts (if it's a standard trigger). try swapping the disconnector first. they are a wear part. if that doesn't fix it (hold the hammer back while the trigger is pulled back) then try swapping hammer and disconnector.

if it's a 3rd party trigger, the problem could be the trigger wasn't mfg'd correctly and you might need to send it back.

just don't start grinding or sanding on anything

even if you get it partially fixed so that the bolt goes into battery, it still may not be safe to shoot. you need to perform "the function check". dry fire it and don't let go of the trigger. manually cycle the action. let go of the trigger. when you do, you should hear a "click" sound which would be the disconnector letting go of the hammer. that means it's good to go. if you don't hear that sound, it's not safe to shoot.

crepe myrtles, eh? woohoO! we're in the Deep South now!

 

[BigJon]

Thank you taliv. I have a technical book on the way, and I'll be diving into it when it gets here - figure these days, it can't hurt to know how to repair the rifle in the field if necessary.

I deeply appreciate the help, you guys. Thanks so much. I'll let you know how things turn out.

Best,
Jon

 

[Seattlefungus]

I've seen this type of malfunction in AR's. At times, firing AR can blow out a primer. It happens at times and the primer can fall into the fire control parts. I've also seen the disconnecter spring fail, (Double tap blocked hammer travel), do to hammer follow. (As the AR uses a free floating firing pin.)
A good set of spares to keep in a kit is a back-up firing pin, disconnecter with spring, take down detent spring and detent pin, firing pin retaining pin and a set of 3 gas rings. DPMS even sells a field repair kit with a lot of the parts in it. If your AR is a mix of parts, I'd make sure the bolt carrier is AR15, not M16, the same for the hammer. (Some places sold both interchangeably.) One of the things that can get you in a jam if someone on a range reports your rifle double taping in auto. (Sans~ David Oofson last May...)

 

[kolob10]

I vote for a disconnector.

 

[mister2]

I did replace the trigger group a long time ago, but I cannot remember whose parts I used.

Years back I put in a "National Match" set in a Bushy. After several hundred rounds, I noticed the same malf you described and realized the unshrouded FP head was hanging up on the top corner of the hammer.

I must have caught it just as the problem was developing because it ran fine at the range, but as I was cleaning after the last trip, the malfunction would occur when I manually cycled the bolt just before I was to put it away. If I did it with the rifle pointed down, it would return to battery, pointed up, it would hang up every time. I combined original trigger and sear with NM hammer and it functions fine.

As in many situations, I believe there is a tolerance stack-up here, where not only material wear, but variances in center-to-center distances of hammer & trigger pins may aggravate the situation.

Have you tried reinstalling the original set to see how it runs with that?

Good luck,...and it's always good to have the book.

MR2

 

[BigJon]

Just reporting back that this was an easy fix. Finally got around to tearing the AR down this morning. Discovered there was no disco spring in the gun! Made one up from some spring stock, and good to go (at least dry firing okay.)

Best,
Jon