So I just got done tearing apart and cleaning my knight bighorn. I noticed there is a crack in my nipple. This I second time it has happened since owning the gun. My question is do nipples just wear out and get cracks in them or does something need adjusted on my gun? I'm using knights red hot nipples if that makes any difference. Thanks
Is the hammer in your Bighorn a Universal Hammer in that it has a cone in the nose for shooting 209 primers? I believe that hammer can create abnormal wear of the nipple especially if it is dry fired. Even shooting a live load the universal hammer can abbreviate the life of a nipple.
Ya its the hammer with the cone on it. I don't ever dry fire it, I always pull the trigger and let the hammer down slowly. Is there anything I can do to fix it or just keep replacing nipples when they get cracked?
Well... that depends... If Washington allows 209's are you going to want to shoot 209's in a Red Plastic Jacket? - If that answer is yes - then you are going to want leave it as it is. But in all honesty there is not real advantage to shoot 209's versus #11 Mag Caps as an ignition source.
The
new Knight Nipples labeled -
Red Hot Replacement Muzzleloader Nipple 2 SKU: M900013 are hardened to higher degree than they have been in the past and will last longer.

The other possibility is to modify the your current hammer by removing the cone on the face of the hammer.
If you take your current hammer to a machine shop - they can mill the cone flat.

I personally would mill the cone even a bit farther than this to make sure the face is flat enough to cover the whole nipple.
You could go online - possibly Ebay or Gunbroker and find some one selling an old percussion cap hammer like this one.
https://www.ebay.com/itm/KNIGHT-MUZZLELOADER-HAMMER-ASSEMBLY/232687430832?hash=item362d406cb0:g:VvgAAOSwc6JadFJNIf you look at the picture of this hammer you can see the hammer at the nipple end has a different shape than your hammer - that indicates it is a percussion hammer. It will slide right in and replace your current hammer