I bought Mosin twice, but couldn't see why you like it so much. The damage is not as great as SVD and DSR-1.
Yap ! I noticed that too. He took a different path no my second playthrough (I completed my second round, was able to defeat Liquid Ocelot without dying ;-) )
Damage? It's a tranquilizer sniper. There are only two tranq guns - the MK and the Moisin. For non-killing sprees it's essential. One shot to the head and they are asleep. One shot anywhere on the body and they asleep within 10 seconds.
And why would you buy it twice? lol...once is enough for however many times you want to play through the game.