I wonder if anyone can help. I bought a Model 29 back in 1980 serial no 471*** I was told by Smith & Wesson that it was a 6 1/2 ins version made in 1978. It has several barrel markings which i have not been able to identify, on the left of 44 Magnum is NP with a mark above. Under 44 Magnum 13 Tons,which i presume is the tested barrel pressure & on the right 1.28" It is an excellent revolver which has been with me many years, any help would be appreciated. I did read that after 1969 the Model 29 had 6ins instead of the 6 1/2 ins barrel.