Or is it a case of asking 'how long is a piece of string?'
Q: What is the maximum killing range for a 100 grain .243 bullet? What distance is it before the bullet runs out of energy to kill the beast humanely?
A: The simple answer is that the maximum range at which you should shoot is that at which you can guarantee your bullet will land within a couple of inches of your point of aim.
In other words, the range at which the rifle will shoot a four inch group.
Most modern rifles will do that at 300 yards – but not when they are attached to someone who has crawled 50 yards along a ditch and forced a gap in the hedge to get a clear shot while lying awkwardly across a protruding root, a piece of barbed wire and an empty oil drum.
That may reduce the ethical range to well under 100 yards. You are the best judge of this.
Producing a clean kill
Now we should address the part of the question which refers to the maximum range at which a truly aimed bullet is capable of producing a clean kill, and that depends on two additional factors.
First of all the amount of energy required needs to be considered and then, what type of bullet will expand and deform so as to apply that energy to the target animal at the reduced velocity of long range.
The question of energy has been hotly debated ever since we discovered how to calculate it and I’m afraid I regard the whole business as being, under hunting conditions, so much pseudoscientific clap-trap.
However, since your 100 grain .243 bullet is still carrying nearly 1000 ft/ lbs of energy at 400 yards, I don’t really think you need to worry about energy.
Then there’s bullet performance, which depends on the bullet’s construction and on its impact velocity.
It must expand vigorously at the longest range while not disintegrating at the shortest. Such bullets do exist – but they are expensive.
The .243 calibre is a user-friendly cartridge for shooting deer, mostly roe, and perhaps the occasional fox at ranges out…
Deer stalking: Is .243 calibre too small for anything other than roe deer and foxes?
Alternative options to the .243
If it all sounds confusing, then you could try something in .30, .33 or .35 calibre. In one stroke this will remove most of your concerns about the .243. Something that’s certainly worth experimenting with.