Sipedon

I have a supernova, and am shooting 12 gauge hornady 2 3/4" slugs through it. No matter how I hold the gun (pulling the slide back, pushing it forward, not touching it) the action opens between 3/4"-fully (and ejects the shell at times) upon firing.Is this normal? I've pulled back on the slide and dry-fired the gun and the slide stays locked until I relieve the reverse pressure. So it APPEARS to be functioning properly. Any input?