Feeding problem with poly side folder

[md10mm]

I was out shooting on Sat. I was using that EG plastic core ammo green case head stamped 05/86. Well i load 30rds and my gun would fire one, eject, load one, but then you squzed the trigger and nothing. I ejected the bullet and there a very light hit on the primer.this happened on about 25 of 50 rds.
I put a clip of wolf HP and had no problems.
I was using a early P.T. side folder wich has never gave me problems before.
Is it my gun or the ammo????????
Brad

[China Sports]

Sounds to me like the plastic core ammo is the problem. EG Made this for urban use, but the weapon was known to not function totally reliably with the plastic core ammo.