remington 1100 problem

I had that problem too on a well used 1100. I'm also curious as to what the problem is.

After trying different types of ammo, I came to the conclusion that it's some kind of spring failure.Luckily, I was able to return the shotgun to the gunshop I bought it at.

Sounds like a shell release or shell interceptor problem.
Either the release or the interceptor is impacted with old crud, or is worn or broken.

Here's an exploded view of the 1100.
http://www.again.net/~steve/ipb-remington-1100.html

The parts to check are the feed latch part 42, or the interceptor part 59.

These parts "time" the release of shells from the magazine. If one has a problem, the gun will allow two shells to be fed from the magazine.

Remington will repair it for a reasonable charge.