do you have a european muzzleloader? the threading on my tc whitemountain carbine is exactly 1/4 28 national fine with a 85% fit. if you have a euro gun, it will prolly have m6x1 fine threading, which means its about .2362'' x 25.4tpi. if you are still using the original nipple, it will have that 25.4 tpi thread which you shouldnt mix with your newly tapped 28 tpi gun. the bright side is that you tapped you gun to the american standard nipple, not a euro thread so you can just go out and buy a nipple for a tc.