Rifle issues

[Seafarinman]

I have an M4 type rifle that I built a few months back using a DPMS lower and parts kit from http://www.blackthorneproducts.com that I have put around 200 rounds through. I was using an old 5 rd mag, and shooting Silver Bear and Wolf ammo today. I was having some stovepipe jams that I can attribute to my magazine. I was shocked when my rifle fired 2 rounds (Wolf) at one time. I cleared the weapon, and pulled the top upper off, and noticed that there is some deformation on the lower receiver around the buffer retainer which seems to indicate that the buffer had been coming forward with a lot of force. This is my 4th AR15, and the 3rd one that I have built, but I don't remember ever seeing that sort of damage to the lower. Could that have caused the rifle to fire the 2 rounds? The weapon has stock AR trigger parts in it and I did not modify them at all. Could they be worn out already? I did function check and I noticed that if I hold the trigger down and pull the charging handle the trigger will lock and I need to pull the charging handle again to reset it. Seems normal to me. The only changes to the rifle besides the ammo was a new RRA M4 stock, and a Troy Industries Medeival muzzle brake yesterday.

http://i11.photobucket.com/albums/a176/seafarinman/100_0682.jpg

[markm]

Is the receiver extension (buffer tube) holding the retaining pin in? Or is it just the buffer itself?

It's hard to tell. Maybe the pic is just a little deceptive. But it looks like the receiver extension isn't threaded in far enough to cover the buffer retainer.

The carrier should stop the buffer from striking the retainer at all. In other words when you close your upper half onto your lower it should take the tension off of the retaining pin. The retaining pin ONLY should hold the buffer when the upper comes appart from the lower.

[Seafarinman]

Is the receiver extension (buffer tube) holding the retaining pin in? Or is it just the buffer itself?

It's hard to tell. Maybe the pic is just a little deceptive. But it looks like the receiver extension isn't threaded in far enough to cover the buffer retainer.

The carrier should stop the buffer from striking the retainer at all. In other words when you close your upper half onto your lower it should take the tension off of the retaining pin. The retaining pin ONLY should hold the buffer when the upper comes appart from the lower.

I checked it and the buffer retainer is itself retained by the buffer tube. Everything fits in accordance with your quoted post.

[Iraqgunz]

demi,

I thought the same thing as well when I saw the picture.

Seafarinman- When you say fired (2) rounds I assume you mean that it went into "auto" mode and fired (2) rounds when you pulled the trigger? If so, check the following;

1. Do you have a 3 position select-fire selector lever or a semi-only? If you have a 3 pos. select-fire then the weapon can fire in auto without a sear.

2. Possible worn or defective disconnector/ spring.

[Seafarinman]

demi,

I thought the same thing as well when I saw the picture.

Seafarinman- When you say fired (2) rounds I assume you mean that it went into "auto" mode and fired (2) rounds when you pulled the trigger? If so, check the following;

1. Do you have a 3 position select-fire selector lever or a semi-only? If you have a 3 pos. select-fire then the weapon can fire in auto without a sear.

2. Possible worn or defective disconnector/ spring.


I have only regular AR parts in my rifle, and I am shocked that they could be worn out after only around 200-300 rounds. I guess that I will take out the parts today and inspect them. I will post the pictures later today.
This only happened once yesterday, but I had a similar occurence 10 years ago with a Daewoo DR-200 that I had installed an Ace skeleton stock and pistol grip on. To make it legal the stock included a "US made" AR15 fire control group. For some reason the parts would somehow fire multiple rounds at any time. It was unpredictable. So I sold the rifle to a gunshop and bought my first AR, a Bushmaster.

[Robb Jensen]

It does look like you can get one more revolution of the receiver extension on the lower.

[Seafarinman]

It does look like you can get one more revolution of the receiver extension on the lower.

You can't see it in the picture, but the receiver extension is screwed in all the way until it is touching the post of the buffer retainer.

[markm]

I have only regular AR parts in my rifle, and I am shocked that they could be worn out after only around 200-300 rounds.

If the parts are out of spec, they'll beat each other up in a very short time. I've had it happen to me in the past.

[markm]

Based on some info in this thread:

https://www.m4carbine.net/showthread.php?t=16859

I'd guess that your buffer detent hole is drilled in the WRONG location.

I think I'd shitcan that lower and buy something else.