somebody gave me an old stevens 620 12 ga. i planned on having the 30 inch barrel cut down to 18 1/2 inches . it seems to be a very solid gun for home defense. i dont understand the loading process. the slide has to be back to load the rnds? i have never used a shotgun that operated like this. is this normal? wasnt there a riot version of this gun? did it operate the same way? is this gun up to the job ?