Just bought a Mossberg accu mag full choke for my 835 and on the package says it can shoot most lead steel and non toxic shot but I've read that you should not shoot steel out of a full choke. This will be my first year waterfowl hunting, looking for some help, thanks.

Most manufactures recommend not shooting steel or steel substitute through the full choke.  I'd personally check with Mossberg of their recommendations. 

X2 what Siebert posted, idk of any manufacturer who recommends shooting steel through a full choke. You really need to pattern your gun, I know its a p.i.t.a. and shoulder too. You'll be surprised how different loads will open up or close down depending on ammo manufacturer. There is a great book called "Shotgunning the Art and Science" Bob Bruster I think. Anyway there are so many variables involved in how a gun actually patterns, I was amazed how differently my guns would shoot. My old Remington 1100 had a modified choke but patterned as extra full using Turkey loads and modified using light field loads, and didn't pattern buckshot at all. I had an extra full barrel that patterned improved cylinder with Turkey loads, the choke was so tight that it deformed the shot and I had to many flyers to pattern effectively. If I had tried to shoot steel thru that barrel it would have ruptured. The best pattering gun I had was a Beretta over under, it was back bored with extra long forcing cones, it was a sweet gun. I know that Mossberg's 835 is back bored and has long forcing cones, it should pattern well, but idk about steel shot thru a full choke. I know for awhile some aftermarket choke companies labeled their chokes according how they patterned instead of their actual measurement. What I mean by that is your full choke steel tube might actually measure out as a modified choke but patterns steel like a full.

What they said...... I shoot a stoeger auto and pump, and tend to use Kent most of the time. With that brand I've found that I get the best pattern with steel using my Carlson Extended Skeet Choke.

As per Mossberg's web site!

Can I shot steel shot through all barrels?

No, not all barrels. Barrels with an interchangeable Accu-Choke or Accu-Mag tube system, YES (with proper tubes installed)

http://www.mossberg.com/customer-service/faqs/