For the sake of argument, 5.7x28 vs 5.56x45 for standard issue round

[zinj]

In Vietnam the 5.56x45 was actually shown to be 11% more lethal than the 7.62x51 - exactly because most combat operations were meeting engagements and ambushes at relatively short range.

How was this figure determined? Not doubting the figure; but was this ratio calculated per round, per engagement, or what?

Laugh though we may now, HK looked very seriously at 4.6mm assault rifles (the G11 and HK36) before they developed the MP7. Some hyper-velocity gimmick you protest? No, both of those rounds developed substantially less velocity than 5.56 NATO ball loads in addition to having smaller, lighter bullets.

Yes, but they were never fielded. History is littered with dozens of examples of technologies that saw significant amounts of R&D poured into them before it was realized they didn't even meet the performance set by the contemporary standard; doubly so when they were given government funding.

 

[GunTech]

Fair question.

IIRC, the 11% figure comes from casualty reports. It is quoted in several of the Ezell books. I'll do some digging with regard to methodology.

 

[HorseSoldier]

Whole premise of the thread is based on a faulty supposition that you can keep going lighter and lighter on a combat round.

We know that combat cartridges are a compromise in weight/volume, kinetic energy and mass, recoil, etc.

We also know 7.62x51 was pretty much recognized as a flop in general service rifles here in the US as soon as Ordnance's cool theory about infantry combat met the reality of the AK-47 (ignoring for the moment the various people here in the US and elsewhere who recognized how vapid the arguments for 7.62x51 were in the first place, based on data going back to, oh, 1917 or so . . .).

5.56x45 was a better optimization. The goal is finding the sweet spot, however, not infinitely paring down bullet mass and velocity.

 

[GunTech]

It also depends on what you are seeking. Some of us are interested in the possibility of a universal military round, that can be used for Rifle, carbine, DMR and MG - replacing both 5.56 and 7.62.

Obviously such a round will be a compromise - but as already noted, every round is a compromise. But the 6.62x5 is basically a variation on the hundred year old 30-06, and even the 5.56x45 is 50 years old. Moderate weight bullets with good BCs can outperform the 7.62x51 at longer ranges with less weight and recoil, and equal or better 5.56 at shorter ranges.

The idea round is light in weight, accurate, has little or no recoil and is effective past 100 yards. You aren't going to get everything you want. But you should be able to streamline logistics and be able to get a round that does everything pretty well - at least as far as an infantryman is concerned.

 

[GunTech]

Of course, we are basically now getting back to the same material already covered in the 'ultimate combat round' thread.

 

[buzz_knox]

It was specifically designed for use in a submachinegun with a bullet designed to penetrate body armor.

The PDW concept was intended to produce a weapon that would be easy to use by support troops and was able to penetrate the armor worn by the enemy. The P90 and MP7 epitomized one answer to the concept, by providing high capacity light recoiling automatic weapons that had greater range and ease of use than the MP7. Other answers included saboted 9mm rounds in machine pistols, cut down ARs, etc.

It's worth noting that body armor technology has improved greatly since the 5.7 and 4.6 were designed. There's substantial question as to whether it can currently fulfill the mission it was designed.

 

[MTMilitiaman]

Maybe I read it wrong but I didn't get the idea he was proposing x28 as the end all and be all so much as questioning the original reasons for abandoning .308

DINGDINGDING! We have a winner!

At least someone can read...

I already specified that I was playing Devil's Advocate here. I am not a big enough poodle shooter fan to actually propose we go any lower. But the logic is the same.

First you observe that most combat takes place well within the effective range of the currently issued cartridge and that modern infantry has to carry a lot of crap, so reducing weapon load is a good idea. Then you propose a compromise to a small, shorter range cartridge that is still likely to be effective at the majority of current engagement distances while providing both lighter weight and less recoil. Then you use a lot of fancy wordage that politicians are likely to be impressed by, even if they don't completely understand, to describe the construction and effects of the projectile and exaggerate its effectiveness, and awe them with some exploding watermelons, explaining that it will do the same thing to the human body. And with the right political connections, wha-lah! The 5.56 is now your standard infantry cartridge. O, did I say 5.56? I meant 5.7

The 5.7x28 is actually intended to fill roughly the same role as the M1 Carbine. It is my understanding that this rifle was never intended to be standard issue on a large scale either, but despite claims of it failing to penetrate thick Korean winter garb, most units seemed to find it effective enough, and liked its light weight. If my understanding of history is correct, the Carbine, originally intended primarily for officers and REMFs as an alternative to the 1911 Colt, then found its way into Armored Cav and Airborne troops, and then into the general populace. I could be wrong here, but again, the philosophy was similar to the creation and adoption of the 5.56--sacrifice range and power for weight and controllability under the pretense that the round will still be effective at commonly occuring engagement distances.

Acknowledging that the average engagement distance in Iraq is rumored to be under 100 yards, the 5.7 doesn't seem like much of a stretch. Especially since nobody is suggesting we give up the 7.62 and .50 BMG in the support roles.

 

[Joe Demko]

7.62 x51 wasn't considered a success when it was the general issue round. It's not coming back as such, either.
Whatever replaces the 5.56 will be an "assault rifle" cartridge of some type.

 

[buzz_knox]

The problem with this line of argument is that it misses the fact that the 5.7 on its face does not fulfill the necessary requirements for a service caliber that had largely been agreed upon before and after WWI, WWII, and Korea. The 5.56, by contrast, met those requirements. One can argue over how well it does, but the 5.7 would be a nonstarter even as an "intellectual" excercise.