M&P 15R Fail to Fire Question

[DevinLSU]

I am new to the forum and to my M&P 15R and need some help. I bought a 1080 Round Can of Surplus Russian 5.45x39 ammunition. Features a Steel core 53grn full copper plated steel jacketed bullet, lacquer coated steel case, and berdan primer. It seems that every 4th or 5th shot fails to fire. I can see the primer has been struck. Any ideas on how to fix this? I greatly appreciate your input.

Thanks!

 

[Breechloader]

Do you try to fire them again and they work?
I mean if there is a dent in the primer then it seems it should have fired if it was good.
Bad ammo or a light strike by the firing pin.

 

[DevinLSU]

I did not try to fire them again. The puzzling thing is not every round fails to fire, just every 4th or 5th.

 

[Nathan Forrest]

You might try taking the bolt apart and cleaning out the firing pin channel w/ pipe cleaners. Maybe its gunked up .