I'd keep the box in tact, and not use any ammo from that box or any other box with the same lot number. Contact Magtech and let them know what you discovered. I've had issues with their ammo in the past (got a box of squibs). They're really easy to work with. They sent me a box with a pre-addressed UPS shipping label. I packed up the offending boxes of ammo into the box they provided, took it to UPS, filled out a bunch of forms after answering a bunch of questions and that was it. About 2 weeks later I received a letter in the mail thanking me for bringing a "production issue" to their attention along with a letter to take to my local gun shop to pick up replacement ammo. When I got to the gun shop, the owner told me that he got a call from Magtech giving him a heads up that I was coming by. They replaced all of my ammo (5 boxes of various calibers) and authorized me to pick up 2 more boxes of the ammo of my choice.
Things happen when products are mass produced. Even with various stages of CQ, some defects are bound to slip by. I'm glad that Magtech took responsibility for what happened and made things right. Considering that things could have been a lot worse (bulged barrel, blown up gun, etc.), a few boxes of ammo is a small price to pay for them. Replacing my ammo and hooking me up with a couple of extra boxes may have been a minor expense to them, but made a HUGE impact on how I perceive them as a company and how they do business. I've had similar experiences with CCI Blazer. Different problem, but similar customer service experience.
Hope all goes well and you get the issue settled.
gf