I also own a 1300 Black Shadow and mine does the exact thing your described. If you read some more literature on the 1300 you will find the gun is designed to do this for a quick follow up shot. It is almost like a cross between a semi-auto and a pump. If I remember the information I found that describes this dealt with the rotary bolt feature. This is perfectly normal with this gun. I bought an Undertaker choke and am shooting 3" Winchester supreme's Double XX's #6's and getting 50+ pellets in the head kill zone at 30 yards. It did a great job last year on the PA bird I killed.