The 45/70 is one of my favorites to hunt with.On deer size game a 300 grain round will plant any deer.There is plenty of factory ammo for sale and different power ranges.Remington 405 grain are some of the lower end while the buffalo bore and garrett being the upper end.(they should only be shot in a modern firearms)This question is ask all the time and to answer it very easy -- that round almost elimanated the buffalo so on deer its a snap.The 38/40 I have no experince with but I am sure you can find ammo.