I have not owned a 243 or a 6MM Remington in many years, but I did own both at one time and I killed deer with them. I have seen a lot of deer, antelope a handful of elk and one moose killed with 243s and having been a hunter as well as a guide on and off for the last 40 + years I can say with certainty that a 253 with a good bullet is a wonderful deer and antelope rifle. In the hands of an expert hunter and a good marksman, it's antiquity killed most game in North America.
Because I no longer have a 6MM bore rifle I am a bit out of touch with what is available in factory loads but one I have seen used in the last 8-10 years with excellent results is the Federal Fusion.
If I ever get another I will probably simply load the old 100 grain Nosler Partition that I used 30 years ago. Or I may try a Barnes X or GMX by Hornady or any of the good bonded core bullets made today.
Others here may have better and more timely info for you, but as far as feeling nervous about the caliber, you have no reason to.
Be assured, a good 243 is just fine as a deer rifle. What is available today is even better then most ammo and bullets available in the 70s-80 when I used the 243 and 6MM Remington, and they were both good then.
They are better today then ever.
