Which would be the better choice for deer?

They are ballistically very close. And of course as you probably know, the bullet is the same. 243 ammo and brass is way more plentiful. I have a 243 and my buddy has a 6mm, he wishes he had the 243 for ease of ammo purchase. He does however get almost 100 fps more out of a 100 grain bullet. Whatever. Get what you want. Theyre both great,EJ

The availability of ammo for the 6 mm is limited. The 243 would be a better choice if you don’t reload...

On paper they are very close but I have had better results with the 6MM Remington. Quite a bit better.

Others on the forum have said this but here goes. The 6mm (or 244 rem) is a great heavey varmint cartridge. But it doesn't do so well with heavier bullets. As far as I know, there is no factory 6mm of over 100 grains. My 6mm shoots the 80 gr bullter beautifully but it shoots the 100 grainers very badly.
The .243 has a much better time shooting heavier bullets and there seems to be a better selection of ammo. Although I don't own a .243.
My favourite small caliber for deer is the 6.5x55 or 6.5 sweedish. 140 grainers are available and the round is usually accurate with a good ballistic coeffiecient
for what it's worth
okcmco

The 6mm (or 244 rem) is a great heavey varmint cartridge. But it doesn't do so well with heavier bullets. As far as I know, there is no factory 6mm of over 100 grains. My 6mm shoots the 80 gr bullter beautifully but it shoots the 100 grainers very badly.

There are loads in 6mm over 100gr. I shoot 105gr remington extended range flat based. I've never seen a 6mm that wont handle a heavier bullet mine shoots the same with any bullet and i shoot in it from 80-105 accuracy is always great. You may have a 244.rem which doesnt like bullets heavier than 80gr due to the rate of twist.In the 6mm rem though they corrected that and it has no trouble handling a heavier bullet. Ifind it to me alot better on deer size game over the 243.If it was me i'd pick the 6mm over the 243 any day hands down.

I think the twist problem went away about 45 years ago when the 244 was dropped and was introduced as the 6mm the next year.

If you plan to use it for predator either is fine, I'd go with the .243 because of loads availible. If for deer, I would say go with a .25-06. Flat ass shooting gun. I have a Savage and love it.

Of the two I would pick the 243. More ammo choices availible. Great caliber for deer!

Fat-Arrow

Actually, there isnt a dimes worth of difference between the two in the speed arena. You can see 100 fps difference between two rifles of the same caliber, shooting the same ammunition. If you lean toward the 6mm Remington, make sure you check the twist. Early 6mms would not stabilize heavy bullets well. The 243 was designed from day one to handle 100 grain bullets.