Man Wildturkey I am usually not one to keep things inside so here goes. I believe you are saying you were deer hunting with slugs using a 21 shotgun barrel with just a bead front sight. Am I correct? If that's the case then IMO you shouldn't even have been hunting deer with it unless you were using buckshot AND buckshot was legal.
There is simply too much error using that kind of set up and we owe it to the game to make a humane kill. Yes even rifle shooters make errant shots as well as bow hunters. But to do this with a shotgun without sights is just wrong in so many ways.
And to make it worse is you already have the optics to put on the gun and didn't want to "waste" the money sighting it in. Now you went and wasted a perfectly good animal. Sorry but that is just despicable to me. I'm sorry you lost the buck. More for the buck than for you however.
Next time use sights.