i disagree with the 243. for scientifice reasons that i wont get into here, the best choice for an intermediate round is the old 6mm remington, it is one of the best cartridge designs ever made, super long and flat trajectory, next up woudl be the 6.5 swedish. Avery mild mannered round with a very high b.c. and s.d. , more than most other rounds ever invented. {snip}the 243 does exactly what most guys say here that it does, but it was a terrible cartridge design fro that round, because it is highly over bore, to much unburnt propellant, internal bbl ballistics, show terrible pressure spikes with this round, etc., etc. And look, i like the 243 round, but i dont have one because of their terrible internal characteristics. the 6mm and the 6.5 are far superior in every way.
Most everything mentioned in the above post is correct. However, I view it as totally irrelevant. Lets take a look.
243 vs 6mm remington. Yes, the cartridge is designed a tad bit better. It has thinner brass at the back, a 26 degree shoulder vs 20, and is 0.2 inches longer overall. This allows it to have a very slightly greater powder capacity. However, this would make it even more likely burn it's powder efficiently. After all, the new trend in cartridges is 'fatter, wider powder stacks are better.
Let's talk 'overbored' A cartridge is "overbored" if a maximum charge of the bulkiest appropiatepowder still leaves an air space between the top of the powder charge and the bottom of the seated bullet. Alternatively, people use the term for long, high powder capacity catridges, where that extra powder doesn't matter because john q shooter is using them in a standard 22 inch barrel, where that longer powder stack isn't burning fully before it 'runs out of runway', Hence a person with a 300-378 winmag in a 20-22 barreled gun woudl be considered 'overbored' as he would get equal performance from a smaller cartridge, he is just blowing the excess powder out the end of his gun.
But wait! 6mm case is actually LONGER and has a slightly higher powder capacity, hence it is more likely to be overbored, by either definition. Except neither are overbored. There are lots of hot .24 and .25 proprietary and wildcats much longer than either, where the term overbored might apply, but it sure doesn't here.
let's talk superlong, super flat trajectory. 6mm vs 243. I swung over to
http://www.remington.com/products/ammunition/ballistics/comparative_ballistics_results.aspx?data=R243W3*R6MM4*R65SWE1 and selected 2 identical weights and bullet design for 243 and 6mm, and threw the 6.5 swede in to boot. Lets take a look. At 200 yards, the 243 is 2.0 inches low, the 6mm 1.8 inches low. At 300 it's 10.4 vs 9.3. At 500, it's 45.4 vs 40.8, but really, for a new shooter, 500 is irrelevant, hell 300 really pushing it, but there you go. Now lets look a the swed. It's zeroed closer, so by accounting for that, it's 3.3 low vs 2.0 at 200, 15.5 vs 10.4 at 300. Not that far off really, but as far as 'flat trajectory' is concerned, the swede is inferior. That debunks the whole ' the 6mm and the 6.5 are far superior in every way' theory.
So yes, in this case, the 6mm shoots a tad flatter. We are talking mosquito differences, but they are there. At least for deer weight loadings. What about where flat trajectory really lies? Light weight varminty loads. Let's see. Oh, would you look at that. Remington arms lists 7 different 243 loadings, but only 1 each of 6mm and 6.5 While a 100 grain 6mm might have a flatter trajectory than a 243 100 grainer, it sure doesn't shoot flatter than a 243 with a 75 grain. So lets swing by federal. Look, 10 loadings of 243 vs 3 of 6mm. Here again, comparing apples to apples with 80 grain loadings, the 6mm is a tad flatter than the 243, but federal also provides a 70 grain and a 55 grain 243, and those to fly flatter than the 6mm 80 grainer. So for where flat matters, the 6mm looses out.
And that's really the crux of the issue. Every praise you can heap on the 6mm is 99% as true for the 243. Same for any complaint. The real issue is that you may not find the best bullet weight or type for the application you desire if you have a 6mm vs a 243. And remember, we are talking new shooter first rifle. If you want to talk handloaders, yea, the 6mm is better, but you got a lot more exotic rounds that 6mm remington that will outperform it once you get into handloads.
And yes, the 6.5 has got a great ballistic co-efficeint. And guess what. If you have to use a light to medium centerfire rifle vs a grizzly, and your choices are a .243 vs 6.5 swede, take the swede. Same if you want to drop, realistically, an elk. But, just like handloading, that's not what we are talking about. If you want to state the 6.5 swede is a better general use chambering covering target shooting, possibly coyote, probably deer, and maybe elk, or even bear in a pinch, I'd agree. But that isn't what is here.
For whitetails, both the 243 and the 6.5 swede will do just fine. For fun target shooting with a stock rifle, both will do just fine. For varmints, both are actually more hindered by the fact that a general purpose rifle is going to have a 22 inch thin barrel rather than a long heavy varmint barrel. But even then, the 243 is going to provide a better off the shelf varmint round, and shoot flatter.
