Went to the range today and shot my new AR.  Winny white box ammo and some mags that I cannot tell who the manuf. is.

Anyway--on a specific mag I had several failures to feed and the bolt was still an inch from being completely closed.

I am wondering if this is the result of Winchester white box 55gr. and/or a bad mag.

On the mags:

These are steel 30 rdrs that 'look' 99% like the Brit mags, but have a gray coating on them and nothing on the floor plate.  Anybody know?

Quoted: I am wondering if this is the result of Winchester white box 55gr. and/or a bad mag.

I will tell you this, I had some orlites and some cheapo ricos for mags and they all caused problems, and for a long time I hated my AR and was going to sell it. Then I bought some USGI,Colt, & Bushy mags and they work flawless and I'm happier than a pig in shit with it, and it's now my goto rifle. So order a mag from bushy or check to find some cheap USGI's. They make all the difference in the world.

eta:spelling fix

JHill, how many times had you used that magazine before?  If the answer is "few to never", empty the mag, then take a ruler and cycle the follower about 2 dozen times.  This will "seat" the sides of the follower against the mag's walls and make it move much more smoothly.  Remember that the Brit mags are brand new and their sides are still rough from their parkerizing - this helps wear down the high spots.

If we had gotten these mags used from the U.K. instead of brand-new surplus, we wouldn't have this problem.