Glad to get you stirred up. It's a great gun. You'll see other posts on this forum about people using the 1858 for Elk and other big game.
I only use the battle sights. 60 yards or less I have to aim low, 65 - 125 I put it right on, 130 - 175 yards I aim a just a couple of inches high. This year hopefully I will have time to target practice at 200 - 300 yards. It does haves some quirks I am working on also. It shoots better fouled than squeeky clean. My first shot is really off (snipers zero it's called), so I load the gun with a usual hunting load but instead of a bullet I use a cloth patch and fire. This also has insured me of no misfires later when I take my first shot at a deer. Mine likes to shoot to the left also, so I use a little kentucky windage.
Last year was my first year using it. First shot at 150 yards it vaporized the left lung and went cleanly thru the heart and right lung and exited the deer. The nice sized doe ran about 25 yards and died before she hit the ground. The next deer I shot at was another doe, this time she was running instead of standing at about the same yardage (my dad was with me this time cause he wanted to see what this "gun can do"). I hit her in the back quarter at the hip, the bullet travelled down the entire femur (leg bone) and exited around the knee. She ran by 2 other guys with shotguns (75 yards or less)and they missed all of their shots! She ran about 75 yards and died. I turned everyone in our 20 man hunting party into muzzleloader beleivers after that.
This year I was in my treestand (with a cousin from Indiana, who wanted to see what this "gun can do".) I shot a 4 pointer at 60 yards in the head ( I was aiming for the chest, but got a little excited opening morning and pulled back when i fired), dead before it hit the ground. He's a beleiver now too. My second deer was from the same treestand about 10 yards from the buck and I forgot to aim a little low and hit her clean thru the neck and she was dead before she hit the ground also. The power of the 58 is unreal. All of my shots have passed thru the animal, even the head shot (came out its ear). I have a 50 caliber Hawkins too and compared to my 58 it is like a bb gun. That gun is collecting a lot of dust too.
It's a fun gun to target shoot with too. They are 9 + lbs, so it absorbs a lot of the recoil and everyone (shotgun hunters) are surprised how little it kicks compared to a centerfire gun.
It can get heavy carrying it on deer drives, but its worth it.