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The .270 is a LONG action sort of cartridge. Somebody can correct me if I'm wrong, but I'm fairly certain that it's based on the .30-06. The good ole .30-06!

Also based on .30-06 is .308 Win (A.K.A. 7.62 NATO...pretty much), and .243 Winchester is based on .308 Win. As a matter of fact, I've run .308 cases through the .243 die, and created .243 cases! I think there's supposed to be a "step" die, and it probably wasn't the "nicest" thing to do with a thick MILSPEC .308 case, but it DID work!

A qualified ballistician could probably go into a LOT more detail than I can here, but here's how I understand this whole "5.56mm VS 6mm" debate.

First off, from what I've read it seems that selection of the 5.56mm (.223 Remington) was a political decision. Only now, some 30 years (or more) later are politicians catching up to the fact that the 5.56mm round is generally underpowered and not very good at stopping man sized targets at even moderate distances.

Most states in America don't PERMIT hunting with the .223 Rem round because it just doesn't knock down deer sized critters! Yet, it's our standard service round for rifles! Go figure. :-)

The whole reason the 7.62 NATO round was adopted was because it was discovered that with bullets up to 150gr, equal performance to .30-06 was achieved. THIS is a true! Since it's a shorter cartridge (by some 8mm if I remember correctly), a soldier could carry more ammo. At one time, the DoD had either adopted the M-14, or was thinking about it. As I remember it, the M-14 beat out the FN-FAL but not by much. I don't know much about those details.

Anyway....about the "debate". The whole problem is mostly presented in a factor known as a "ballistic coefficient". Otherwise known as the BC. The BC of any given projectile is it's ability to overcome all exterior forces and stay aloft at an acceptible velocity. BC is usually expressed in decimal numbers because a BC of 1.00 is LIFT! NO projectile fired from small arms has a BC equal to 1! Technically, all projectiles start falling shortly after leaving the barrel! A high BC would be .500. A low BC would be .300 to .100 or so.

To give you a more realistic example, 110gr .308 FMJ bullets have a BC of .144. 200gr .308 Spitzer bullets have a BC of .556! As you can probably guess, the heavier Spitzer will have a much "flatter" trajectory! Unfortunately, it also has a MUCH slower muzzle velocity on account of its weight!

So what to do? Smaller, lighter bullets have LOW BCs and are relatively ineffective at typical "contact" ranges for infantry riflemen. Heavier bullets have HIGH BCs, but travel slower.

The answer is to find the "ballistic match". A ballistic match is a combination of three things which produce as near a perfect cartridge as possible. Currently, there are TWO known (agreed upon) ballistically matched cartridges. One is the .30-06, and the other is the .50BMG. Given their case capacity, bore diameter, and suitable, available propellants, these cartridges are both as close to perfect as we can get.

Notice, I mentioned that propellant as a factor in a ballistically matched cartridge! Since propellant technology has advanced in the past 20 years, there are other (disputed) ballistically matched cartridges now as well. These use mainly 6mm (.243) and 6.5mm projectiles. The reason being is that a high BC can be maintained, along with sufficient weight, in order to deliver a lot more energy onto a target. For example, a HEAVY 5.56mm bullet weighs 70gr and has a BC of .214. NOT very impressive. It will exit muzzle at approx 2800FPS. A HEAVY .243 Win (6mm) bullet will weigh 110gr and exit muzzle at the same velocity, but it has a BC of .443!

I haven't looked up the differences in energy delivered by 5.56mm as opposed to 6mm projectiles at distance, but as I remember the differences are BIG! The heavier 6mm bullet flies a much flatter trajectory, has a farther midrange trajectory, and delivers SIGNIFICANTLY more energy onto the target!

The bottom line in this issue is that the 5.56mm projectiles simply don't have enough mass to transfer sufficient energy for a "knock down". Heavier bullets only produce less velocity, and since it's bore size is so small, there hasn't been a propellant designed yet to overcome this problem. It's not likely that somebody will design one for this purpose either!

One the other hand, 6mm, and 6.5mm cartridges permit slightly slower burning powders, a wider range (including HEAVIER) bullets, and identical velocities using these heavier bullets! A 6mm or 6.5mm projectile is a great choice IMHO. I'd personally love to see our soldiers carrying weapons firing the .243 Win on the battlefield.

From what I've read, planners are leaning toward 6mm cartridges not only for reasons I wrote about above, but because it's feasible to control a select fire weapon chambered for cartridges such as the 6mm Remington, .243 Win, and 6.5mm Remington. I'm a GREAT fan of .308 cartridges, but it's a FACT that .308 infantry weapons (such as the M-14, and FN-FAL) can be DIFFICULT to control using full auto. Especially from any non-supported stance. A LOT of ammo gets wasted.

As for the 6.8mm round. I've only read a little about the development, and experiments. From what I've read, they're trying to get the "best of the best", and a 6.8mm projectile seems to be IT. From what I know about 6mm rounds so far, I suspect they may be onto something.

I hope this cleared things up a tad. As always, it's my opinion only. A collection of ramblings and rants based on observations, and readings over the months and years. :-)