I flew to Nevada last summer with 11 firearms in one case (double sided rifle case) via Delta - Honestly though, I have to recommend against it - When I got to my destination, my gun case (one of two checked bags) was missing, and it took two days for the airline to find it. When they finally did find it I received it with the handle broken off, two of the latches missing and one hinge broken. The case had tool marks that showed that somebody had attempted to get into the case. Fortunately everything inside the case was intact and unmolested.
On discussing the issue with Delta, I was given a $25 voucher for my next flight which I ripped to shreds and handed back to the executive politely. I canceled my return ticket with Delta and flew home via American Airlines and had no problems.