If it has a folding stock, a tennis racket case might work. A folding stock M1 Carbine (folded) fits in a single racket case, while a double racket case has better support for the weight and more room for accessories.
I have the LWRCI case, and used it a few weeks ago. I had two rifles I was taking through a busy public place, one in the guitar case and one in a standard rifle case. I actually made two trips so I could use the guitar case twice as no one gave it a second look. On the way out I stuffed both into the LWRCI case. It zipped closed, but is's designed for one.