Can somebody explain to me what just happened?

[harmonic]

I took my brand new Performance Center S&W M&P 15 in 5.56 cal with 20 inch stainless varmint barrel to the range today. I was shooting Federal factory ammo.

I loaded four rounds into the mag.

First shot. "Bang! Wham! Kerchunk!" I thought, "Man, this thing is as wild as my mini 30 (which ejected spent cases into the next time zone)."

Second shot. "Bang! Wham! Kerchunk!"

Third shot. No third shot. I looked down and the bolt was locked back w/an empty mag.

I had just fired two two shot bursts.

It happened once more in the second mag. I tightened my grip and executed a more positive trigger pull. But I was able to finish the session without any more two shot bursts.

What happened?

 

[WardenWolf]

Welcome to bump firing. Recoil, combined with your hold caused you to move the trigger just enough to fire it again. It's called bump firing. Many people do it on purpose because it's like legal full auto that requires skill.

 

[TexasRifleman]

Yep, sounds like bump firing.

The first time my wife shot my AR she did the same thing, which is why I only put 2 rounds each in the first 10 or 12 mags she shot.

Pretty common for new shooters, the light weight of the AR can make you relax on the grip sometimes.

 

[gvnwst]

What Mike the Wolf said. A few match triggers take care of this, mine locks the hammer back to i have to completly release it before firing. makes bump firing hard. Unless i am just doing it wrong.....
It usually takes pratice to do what you are doing! Feel good that you learned to do it early on!

 

[harmonic]

Well, I'll be. Now I bet I couldn't do it again if I tried.

 

[Kind of Blued]

Just for giggles, go make sure you have a disconnector.

I'm serious.

 

[taliv]

interesting theory
i'll admit i would not have have guessed that

my initial thought was same as blued's. bad disconnector

 

[ravonaf]

Question from a newbie. How do you make 100% sure it was a bump fire and not a malfunction. From what I understand a malfunctioning semi-auto can land you in prison.

 

[hadmanysons]

I've gone through about 100 round on my AR-15 trying to get a good feel for bump firing and now i'll do it even when i'm not trying to or WANT to. I've taught myself how to hold that way that it will bump fire when i'm trying to sight something in. Really annoying.

 

[benEzra]

Question from a newbie. How do you make 100% sure it was a bump fire and not a malfunction. From what I understand a malfunctioning semi-auto can land you in prison.

Two things.

To rule out a sticking firing pin causing slamfires (hazardous), field strip the rifle and make sure the firing pin moves freely back and forth. If it gets stuck in the forward position, it could cause a slamfire, which is hazardous.

As a quick check for trigger group problems, make triple sure the magazine well AND chamber are EMPTY, then lower the bolt on the empty chamber, point the rifle in a SAFE direction, and pull the trigger and hold the trigger back. The hammer will fall with a click. Still holding the trigger back, grab the charging handle with your other hand and cycle the action; the hammer should not fall. Release the trigger, and you should hear a click as the trigger resets, hammer still back. Pull the trigger again (still pointed in a safe direction), and the hammer should fall again. Repeat a few times. If the hammer falls while the action is being cycled with the trigger held back, the trigger group is defective, big time.

IMO, if the rifle ever does it again, contact S&W. Both slamfires and hammers falling when they're not supposed to are indicative of serious problems, if in fact this was a mechanical failure.

 

[harmonic]

How do you make 100% sure it was a bump fire and not a malfunction.

Well, I'm checking the disconnector. You take the upper off the lower. With the hammer cocked, put your thumb in front of the hammer and pull the trigger. It will release the hammer into your thumb. Lower the hammer while continuing to hold back the trigger. Then with the trigger still depressed, pull the hammer back again. The hammer should lock into place. Mine does. If it doesn't lock into place, then there's a problem with the disconnector.

 

[harmonic]

To rule out a sticking firing pin causing slamfires (hazardous), field strip the rifle and make sure the firing pin moves freely back and forth. If it gets stuck in the forward position, it could cause a slamfire, which is hazardous.

That's the next thing I've got to check.

I'm hoping it was my grip, though. I was shooting off a bench rest, non shooting hand folded back underneath the butt stock, very light grip. Kind of like you might shoot a target 22 in long range competition.

I did that with a 30-06 bolt action once, and wound up with a crescent split in my forehead.

 

[Coronach]

Query:

Were you firing from the bench? I find ARs and AKs very easy to double when you're shooting from a rest. While checking out the FCG and the BCG are not bad ideas, I'll bet this is what happened.

Mike

 

[Coronach]

AH! We simulposted. You bump-fired it.

Mike

 

[SwampWolf]

A two-stage trigger should pretty much obviate "bump firing", even with a light pull "match trigger". Unless you linger too much on the trigger and are applying any pressure. My advice is to make certain you disengage your finger from the trigger after each shot.

 

[W.E.G.]

Work on kung-fu grip.