Not how I wanted my day at the range to end

[The Swamp Fox]

I took 150 rounds with to sight in my AR9 with the new vortex strike fire I bought for it. On round 149 the screws that hold the key onto my BCG were sheared in half causing a major malfunction and putting the rifle out of commission.

A little background on the rifle. It's a build I did about 5-6 years ago before Glock mag lowers were a thing. I used a billet upper and lower set with a mag block to accept stick mags. The BCG is a Yankee Hill 9mm with the weight in the rear. I was running a heavy 9mm specific buffer and buffer spring. Today I was shooting 115 grain Winchester white box ammo from Walmart.

Anybody ever see anything like this?

 

[pirate]

I don't think I have ever seen the gas key fasteners shear off like that. Come loose and cause issues yes but both shearing off is bizarre. Wonder if the maker used grade 8 fasteners.

 

[Slacker]

Happens all the time with Kaw Valley 9mm BCG. I'm sure it happens with other brands also.

 

[JBoyette]

Typical,

Nothing new gater grip the screws and use harden screws.

 

[The Swamp Fox]

Typical,

Nothing new gater grip the screws and use harden screws.

Good thinking.

I wonder if a stiffer spring or heavier buffer would help too?

 

[JBoyette]

Nope.

Think about this.

The rifle is recoiled operated. The "gas key" is a alinement tool riding inside the charging handle.

I would look at the clearance of the charging handle stem

Also does the billet lower have one of the dumb ass tighting screws to "remove" slop between the upper / lower?

 

[Tim]

Happened to my PSA bolt a while back. Looks like exactly the same failure.

 

[The Swamp Fox]

Also does the billet lower have one of the dumb ass tighting screws to "remove" slop between the upper / lower?

It does not. What am I looking for on the charging handle?

I thought if I could reduce the amount of force on the key what when it comes back it wouldn't be so hard on the screws. When it malfunctioned the key fell down in front of the BCG preventing it from returning to battery.

 

[JBoyette]

Just clearance.

Check the stem on the inside. See if you have rub marks towards the (handle) side on the inside. If so flip it over as see if you have marks.

You can play with springs and weights. If you think it will slow it down.

John