For me, the .243 us neither fish nor fowl.
I've seen a LOT of deer lost with the .243 through the years. As such, I'd never been inclined to aquire one for myself after trading off the first one I had back in the early '70's.
This past May, I won a Stevens M200 in a pistol match and was delighted because my older brother aquired one back in the early '90's for my nephew, and he'd had excellent success with it shooting whitetails, mulies, and prararie dogs in Montana.
Fast foward to 3 weeks ago. I shot the first of 2 deer with it at the "long" range of 35yds. The deer bolted at the shot, and in the midst of 3 other deer and a small gulley between me and the first one shot, I lost track of which one I'd hit. I swung on the one I thought was "hit", and when it stopped and looked at where the others had ran off the food plot, I squeezed on it. It dropped, jumped up and ran staggering, falling and dashing out of sight.
I followed the blood trail left after the second, (failing to find blood at the site of the first shot/hit). After 300yds, the blood trail tapered off to nothing and after 2hrs I had failed to find the deer. A bit later, I walked through the food plot taking another new hunter to show him a ground blind approx 200yds further up the hollow from the food plot. While walking through the food plot I was stunned to find another fresh blood trail leading off in the direction two of the "other" deer had run. After following that trail for approx. 150yds, I found the "first" deer dead. The bullet had impacted where held. It had failed to sufficiently penetrate deeply enough through the chest after impacting the shoulder to leave an exit wound. The deer had run nearly 50yds before leaving a blood trail. The lung wound was sufficent to kill the deer, but the largest piece of the 100gr Hornady SP "Interlok" was the base that weighed 10gr.
The shot on the "second" deer was a rear-foward raking shot that took it on the last rib. No evidence of an exit wound was found so I surmise it too "blew up".
In my Game and Fish enforcement career I encountered many such instances involving either assisting hunters in locating a downed deer, or searching for one shot by poachers (hunting w/o permission, or shooting them from road or at night) where a .243 was involved.
My experience coupled with that of my brother/nephew dovetails with that of a number of other people.
This is "my" opinion.........
Like John Barsness recently noted in a "Handloader" article regarding the Speer "HotCor" bullets, the .243 structurally lacks sufficient surface contact between the jackets and core to be able to keep from having the core's slip and separate. Couple this with the jackets being constructed to attempt to prevent core slippage, and premature rupture, the bullets at extented range (beyond ~250yds) where velocity has dropped below where it's sufficient to initiate nominal expandion and the bullet then acts as a FMJ (full metal jacket). I've even seen this at ranges beyond 300yds with the usually excellent Nosler 100gr Partition.
I've had several hunting/working aquaintances use and then abandon the .243. This is remarkable, as I've had outstanding success with the .22cf's, especially with 55gr and heavier bullets. I've always however been particular about shot placement with the .22's, though the one's I've shot in the chest/heart lung area, have always exhibited nominal big-game bullet performance. The only time I've had the bullet failure phenomon is with bullets 50gr and lighter.
So, I suppose that if you treat the .243 the way you would a .22cf when hunting deer, you'll get excellent results.
I had become quite fond of my little Stevens as it was laser beam flat shooting and accurate. However, I forgot it was lying in the case in the bed of my P/U and someone "liberated" it from me. This is the only firearm that I've ever had stolen from me. I hope whoever got it has and AD and shoots their big toe off (as I once investigated a hunting accident where a hunter DID shoot his big toe off with HIS .243), as I'd tweaked the trigger down to approx. 1.5lbs "crisp".
It'll serve him right !!!!!!
I do plan on replacing it "sooon" however, -I have to many cases, components and loaded ammo now, not to have something to shoot it up! The Savage M110's hit the pawn shops in numbers after deer season is over and I should be able to pick an "ugly" one up cheap. I'll then buff of the rust and touch it up with some camo paint, and then off to the range to get it shooting straight........
Before the rifle "walked off", I'd planned on pulling the existing ammo and instead of the 3,000+fps load I was using (42.5gr RL-22 and shot 2/3" groups @100yds w/5 shots) and "down load" them to around 2,600fps. Then too, I was going to pass up on shots beyond 250yds for the same reason I do with my .30/30 and .35's. Insufficient velocity to get good bullet expansion.
I plan on trying some Remington CorLokts as I've heard of some having good success with them even on Elk. Perhaps with a little less velocity for the frequent short shots I get the bullets will hold up a bit better. This is just the reason I went with a .257 Roberts in 1983 when I had a custom rifle built. It has never "failed" like this. Similarly shot deer have always given exit wounds with 100-120gr bullets, and I've only lost one of many dozen deer hit with this rifle, and that one was marginally hit through the lower chest anyhow.
Do shoot straight !!!