If you have to beat it out anyway, check the case for lengthwise scratches. I was at the range on Thursday playing with mine, and another fellow a few benches down was having the same problem no matter what he set his gas to. He asked me what I was doing different and it turned out pretty much nothing.
We plucked one of his spent cases and it had very visible lengthwise scratches. I "happened to have" a penlight on me (because I keep one in my range bag) and we removed the receiver cover/bolt/carrier and took a look inside. His chamber was horribly pitted, I would say beyond any hope of re-polishing. His was a "Wholesale Sports Special" - no one had even given it a passing glance pulling it out of the crate.
It happens. Sometimes the arsenals didn't do much in the way of refurb - just a basic clean and dunk in cosmo before packing them away.
For a decent chamber brush, I find a 12guage bore brush works well. Clean it, scrub it down, take a look.
If the chamber is fine, then yah - it's the gas setting. If I set mine too low or turn it off, then it's out with the rubber mallet to beat the charging handle to extract.