My take on this is 243 will do the job as stated up to & including red hinds - but it is at the lower end of what could be called optimum performance capability for the larger animals.
That's rubbish. The 243 is perfectly capable of cleanly killing all deer species in the UK. That's why the law is written the way it is. (As if that was obvious in itself, I discussed the matter with the draughtsman who prepared the E&W Deer Act. It was draughted to exclude the .22 centrefires.) Red deer are not particularly tough animals, they do not have especially thick hides nor are they heavy boned.
It is a great varmint calibre (what it was designed for),
Go and do your homework. It was designed as a dual purpose cartridge, varmint and medium game, that's why it has a 1:10" twist (unlike the .244 Remington which fell by the wayside and had to be rebarrelled and rebadged the 6mm Rem).
BUT fast bullets (above 2900 ft/sec) often result in bad bruising & carcase damage. They often fragment inside the beast & make a mess.
So can a bullet of any calibre. You cannot lay down hard an fast rules. I have had very clean carcasses with minimal meat damage shot at 60 yards with a 60gr HP from a 223 (MV 3000+) and I have also had a wrecked carcass shot from 60 yards from 140gr SP from a 7mm-08 (MV 2500). In Scotland one week, we shot 16 red hinds with three .243s (each firing a different bullet) and one .30-06. All of them produced similar wound channels and at the end of the week you couldn't have said which skinned carcass had been shot with which bullet.
Another problem with 243 is that it is marginal in meeting the legal minimums for larger deer.
That's not a problem. The 243 is fully capable of the task asked of it, that's the issue. In a BASC survey of stalkers, the majority of professinal stalkers used a 243 - and they were of course north of the border shooting reds - while the majority of amateurs used a larger calibre. What does that tell us? The 243 is fully up to the task. I know two professional stalkers. One is in Sutherland the other in the Central Highlands. One has a .243 and a 270. He uses the .243 himself and the .270 is for guests to use. The stalker in the central highlands has only a 243, and he shoots 160 hinds a year. Neither of these stalkers finds the .243 "marginal".
However bigger diameter 6.5mm to 30cal (heavier) bullets will do a better job, they usually get driven a bit slower (2500 to 2800 ft/sec) and often this causes less meat damage. These bullets carry enough energy to pass straight through creating better bleed out conditions. So IMHO a larger calibre is slightly "better" and more optimum.
I wonder how many deer or other large game have you shot with a .243? On a broadside heart/lung shot, the bullet punches clean through - even at extended range. In 1996, I shot a large doe pronghorn antelope broadside on at a measured 448 paces. That antelope was a similar size to a red hind (excepttheir hearts are about twice the size of a red deer). The .243 95gr Ballistic Tip (launched at 2925fps) punched clean through her heart and left an exit wound three inches in diameter. She leapt up and dropped dead on the spot. There was a cone of bright arterial blood on the blonde grass extending about 20 yards beyond the doe, clean evidence of the bullet's performance. I shot several others including one at 315 paces and another 270 paces. A heart shot in every case, and the bullet performed in a similar manner.
A great many people seem to underestimate the capabilities of the .243. It has it's limitations of course.
Big bullets deliver more energy & result in better knock down
Define knock down. Do you mean the reaction of the pronghorn doe I described, the animal dies on the spot? Or do you mean the red stag I shot two years ago, at a mere 75 yards, which ran off and was found dead 400 yards beyond. Strange, because that one was shot with a 180gr Interlock from a 30-06. The reason it ran off was because I hit it a bit too high and bit too far back. The larger/heavier bullet delivering "more energy" and "knock down" knock it down because it was in the wrong place. A .243 bullet in the right place would have been effective, would have killed the stag more or less where it shoot. If you put the bullet in the right place it will do the job, it can't do it's job if you put it in the wrong place.
And
please no more comments about a bullet calibre/bullet will make up for a "marginal" shot because I would have to drag up the tale of the warthog and two hits from my .375H&H and runing 2km. If the bullet is in the right place then calibre doesn't matter, and if the bullet is in the wrong place then calibre doesn't matter.
FWIW, I generally use a 7mm-08 as my woodland rifle and a .30-06 as my hill rifle. I also have several 243s, and having shot a wide variety of game here, in the US and also Africa with the 243, I would have no qualms whatever in shooting any UK species with it.
-JMS
-JMS