Cause the bullets bounce off the armor of the ones over 220 lbs.

No! but thats the point at which I would avoid a high shoulder shot. With a novice I want them to be able to take the first reasonable shot. On a big deer, I'm not taking a high shoulder shot with anyting lighter than 117/120 gr class of bullet, IMHO anything smaller doesn't give you enough margin.

If you have to ask, then 80 yards.

I think the rule of thumb is it takes 900ftlbs to effectively kill a deer so at whatever distance your particular round drains down to 900ftlbs is the number.

The effective range of a .243 is 343yds. This is with the original Winchester ammo that is lacking with quality. I'd bet anything a Remington or a Hornady would get 375 minimum. The effective range is when the bullets energy in foot/pounds falls below 1000. You make the call where to shoot with that energy. I would personally say a neck shot, because that is the equivalent of a .223 a 50yds.

I've killed many a deer with my 243 up to 200 yds. I also have a 270 and a 30-06 but I like shooting the 243 . It is very accurate too and a very fast bullet. I have 2 243's, a browning and a weatherby. The weatherby will out shoot the browning and day of the week and twice on sunday.

TSX bullets... no worries

I wouldn't hesitate out to 300, especially with a monometal bullet. Physics is not your friend as you get beyond that.

What is an example of a mono metal bullet and what is the significance of it NP?

Dad shot a bull elk in Colorado with a .243, I don't know why everyone thinks you need to shoot a slug at something to kill it!

lots of deer have been killed with a .22 but that doesent make it anywhere close to ideal.

For worst case scenario.

Barnes TSX and several others. Will hold together and penetrate better which helps a lot with the smaller bullets for medium sized game.

Shot placement + sectional density + energy at X distance = kill

Eh?

Moose good formula.

A lot of new hunters never get the first part Shot placement

Based on your skill.