What's the point of blasting away at a fatally wounded and running deer? Every extra hole means wasted meat. A load of buckshot can destroy a hindquarter and/or perforate the guts and make field dressing much nastier than it needs to be. Deer are not THAT tough but there's no sporting arm made that will "blow one off it's feet". If you want to drop one where it stands it takes a hit to the noggin or spine. They're gonna run with a heart/lung shot no matter what. But they also usually drop within a few tens of yards. Follow up shots will likely miss or be poorly placed at best and the noise just amps up the animal's flight response. Not to mention that while you're swinging and blasting at the running deer you probably won't be able to adequately check the background for other hunters. This is why I only deer hunt during bow season.
Take one well aimed shot, sit tight and quiet, note where the deer was standing when you shot it and what direction it ran. After 15 minutes or so carefully and quietly take up the trail. If it is only wounded it should be laying down fairly nearby. That is if you didn't unleash WWIII and immediatly hoop and holler and give chase. If you are close enough to actually hit a deer with a followup shot you are more than close enough to place a single shot that will do the job. Deer are not a threat target that you need to shoot till they stop.