Keep the shotgun if you can, but a muzzleloader is all I use for deer hunting besides bow. A good muzzleloader can be had for a good price. CVA, Thompson Center and Traditions all have some great deals out there for under $250. Pay attention to the rifling though. I wouldn't get anything less than a 1:28 twist rifling. I personally have a CVA Apollo with the 1:28 twist and I love it. I got it 12 years ago and added a 3x-9 Simmons scope. I haven't even picked up a shotgun for deer hunting since then. The 870 would be nice to have on hand though for other hunting purposes.