It has been demonstrated a number of times that a soft lead tip bullet will not ignite the next in a mag tube. It is just a myth, but many shooters would rather believe a myth than admit they are wrong even when shown the truth. When intentionally ignited in a tube by a striker nothing happens, it doesn't rupture the tube and certainly would not blow up a gun. Cartridges do not explode like in the movies, the case just ruptures releasing the gas, leaving a little soot, and a split case. Excitement over.
As Galaxieman said, you don't need pointed bullets in a lever gun, anyway. The round nose and flat points are better killers at lever gun velocities. And the sharp pointed shape doesn't help much until ranges exceed 300 or more yards. Everyone "knows" that a lever gun will not kill game at ranges beyond 100 yards so it's a moot point.