SIG556 Failure to Fire

[MaverickNH]

I cleaned and lubed my new SIG556 Classic, and hand-cycled the action 300 times as well. First 200rd from bag and standing went fine with 100% success.

I did an Appleseed shoot this weekend (http://www.appleseedinfo.com) and ran about 750 rd '87 SA surplus 556 NATAO through prone, sitting and standing with a DPMS M1 Garand sling loop hold and experienced failures to fire at a rate of 0-4 round in every 40rd AQT course of fire.

I pull the trigger, hear the click, no fire and cycle the bolt to eject the round. Never happen 1st round, but sometime 2 rounds in a row. Those same rounds, back in the mag, fire OK. No primer strikes visible at all on rounds that fail to fire, so not a hard primer issue.

Never seems to happen standing, but on sitting and prone when the sling tends to pull my hand to pressure on the mag. I know that can cause FTFeed, but can that cause Failures to Fire?

I'd appreciate some help troubleshooting this problem.

 

[MichaelJR]

Honestly, I didn't think I'd ever see a post about a problem with the 556.

 

[MaverickNH]

Not to mention, the front sight roll pin walked out and the drum fell off. And I only noticed that two of the three Picatinny rail hex screws fell out this morning. Maybe that's why I started missing so badly Day 2. My scope is loose. Just off the phone with SIG and they are sending new parts but I didn't get into the Failure to Fire issue.

 

[Gammon]

Not to mention, the front sight roll pin walked out and the drum fell off. And I only noticed that two of the three Picatinny rail hex screws fell out this morning. Maybe that's why I started missing so badly Day 2. My scope is loose. Just off the phone with SIG and they are sending new parts but I didn't get into the Failure to Fire issue.

This could be a dirty chamber. The fouling is preventing the round from completely chambering so the firing pin is actuall moving the round forward rather than denting the primer. Clean the barrel and try it again.

 

[whatluck]

This could be a dirty chamber. The fouling is preventing the round from completely chambering so the firing pin is actuall moving the round forward rather than denting the primer. Clean the barrel and try it again.

This. I would give that thing a good detail cleaning.

 

[Supermoto]

Is the pressure on the mag keeping the Bolt from returning completely into battery?

 

[MaverickNH]

Is the pressure on the mag keeping the Bolt from returning completely into battery?

Maybe. My struggle is to use a cuff sling hold without my wrist pushing on the mag. The SIG 556 Classic has the front sling mount on the left side by the gas port.