Only one would be the fancy flex tip ammo. The only successful traditional style pointed tip round in a tube magazine was 8mm Lebel, and that is solely because of the taper and the groove cut into the base to catch the point. Otherwise you are just risking detonation for no good reason.
Remember Firearms Instructors are like the guys you meet behind the gun store counters, they maybe knowledgeable, but more times than not they aren't. Another thing to consider is you can't know everything. I know a fair bit about milsurps (always more to learn, but I have a good general grasp), I couldn't tell you much about black rifles, hunting rifles, shotguns, modern pistols and revolvers, or rimfires. Its all about knowing when to say you don't know. That is the difference between someone you can use as a expert or someone that spews nonsense.