Tony Williams Wrote:I don't see much prospect of a new round just to replace 5.56mm. The counter-argument will always be that 5.56mm is normally good enough (especially given M855A1 or MK318) and for circumstances in which it isn't good enough, there are 7.62mm weapons available.Those are very good points, with which I cannot find fault.
Replacing the 7.62mm with a lighter round of equivalent long-range performance is likely to be more attractive to the army (US or UK) since they are very concerned about reducing the huge burden carried by dismounted troops.
By definition, a lighter, smaller-calibre long-range round to replace 7.62mm would also generate less recoil. Having tried HK 416 in 5.56mm and 6.8mm plus HK 417, all in quick succession, I found that the perceived (as opposed to calculated) recoil of the 6.8mm was much closer to the 5.56mm than to the 7.62mm. This makes a long-range intermediate round of similar power a realistic proposition for replacing 5.56mm in rifles and carbines. Yes, there would be some penalty in ammo weight (or alternatively the infantryman would carry fewer rounds) but the greater range and effectiveness of the ammo might well trump that.
Quote:All I've seen are assurances that the M855A1 and the British 5.56mm HP produce more consistent terminal effects, but no evidence in support. But ARDEC did all the testing in different calibres using military-style green bullets and concluded that 6.8mm was best...I'm willing to accept 6.8mm was indeed the best. But, since the only intermediate calibers reportedly tested were 6mm, 6.35mm, and 6.8mm, I'm not at all surprised that 6.8mm proved best.
There's no way to be certain how 6.5mm and 7mm would perform relative to 6.8mm in the same test conditions. However, as has been widely reported in the past, the SPC developers found 7mm gave better terminal effects than 6.8mm, and 6.5mm was worse.
Given "green" bullets of the same type construction, with the same sectional density and shape, and launched at the same velocity, it seems reasonable to think the bigger the caliber, the better the terminal effects, be it penetration of "hard" targets, or wound profile in ordnance gelatin. There's simply no substititute for mass. (Except in the silly, steel helmet penetration test.
)Since the ballistics tables I ran a few days ago show a match to 7.62mm trajectory and wind drift with both 6.5mm 110gr and 6.8mm 120gr (and probably also with a hypothetical 7mm 130gr), I guess the next question is, what trade-off between cartridge weight and terminal effects is acceptable?
If minimum weight/recoil is desired, and minimum effectiveness is acceptable, go with 6.5mm. If maximum weight and recoil is okay in order to achieve maximum target effects, 7mm is the best choice. As with the SPC, 6.8mm would be in between 6.5mm and 7mm, both in weight, recoil, and terminal effects.
Unless priority is placed on really minimizing weight and recoil, 6.35mm and 6mm are probably not worth considering. The farther down we go from 7.62mm, the farther away we get from 7.62mm destructive ability.