M16-A1 light primer strikes

[Baneblade]

I am looking for a little help with one of our department rifles. One of our M-16A1 rifles is encountering light primer strikes on full auto. It seems to be every 5 rounds or so. There is a small mark on the primer, but definately not enough to fire the round. Ammo is not the problem, the magazines are good, the gun is clean. It only occurs on full auto.

I have not had a chance to test fire it yet (we don't have an actual range) and would like some ideas of what to look for beyond the Armorer (Colt M-16/AR-15 certification) level. I have inspected the weapon and there are no obvious problems. I will tear into it today, but other than an early hammer release/timing issue I'm not sure what this would be... assuming the gun is properly cleaned.

Feel free to give me any ideas.

The rifle is a refurbished military M-16 A1 rifle purchased by my department. Serial number is around 1.5 million.

 

[rcmodel]

There is a small mark on the primer,

That sounds like a normal firing pin ding from when the round chambered.
Every chambered round will have a small ding from the floating firing pin if you don't shoot it.

Could it be it just is not catching the hammer occasionally and the hammer is following the bolt down?

Hammer or sear or spring problem probably.

rc

 

[Baneblade]

It is getting more than just the firing pin tap. It appears the hammer is releasing early, but the disconnect is holding it so that it does not just follow the bolt.

 

[redneckdan]

check the timing first.

 

[Jeremy2171]

Pull the hammer spring and ensure one of the "legs" isn't broken.

 

[Baneblade]

It was the sear spring. I had thought it was a timing issue. The spring was intact except for one small part of the leg. The piece that holds spring to the sear was broken so the sear could just flop back and forth.

Thanks for the help. At least it was an easy fix.