An NK would make it a 1996 manufacture. I could be wrong on this, but I think they had transfer bars in this year. Your description of a vertical bar makes me think you have a transfer bar. Those rifles that do not have one only have the hammer to push on the firing pin and should have a half cock position. The transfer bar should fall out of the way when the trigger is not pulled back. If it is staying in the up position it will push out the firing pin when the hammer is down. If it is staying in the up position at all times, it will push the firing pin out. Being in the out position, the extractor will rub against it, possibly wearing it down or breaking off the tip or even bending it. I think your frame should be OK to take a 45-70 barrel, but I would call first just to make sure. There seems to be some thing going on with the transfer bar and it more than likely has damaged the firing pin. When you send it in, they should be able to fix it for you, but you can get parts and fix it your self too. Good Luck and Good Shooting