I imagine they've already considered improved .308 rounds with a longer distance because they would be cheaper than adopting a new round, but they probably didn't cut it. Snipers in Afghanistan went to .300 winchester magnum. And they seem to be switching to .338 Lapua.GarryB wrote:The key is transonic bullet speed.
When bullets change from supersonic to subsonic speed they can be quite erratic and their accuracy can suffer.
For most modern 308s that speed transition is between 800m and 1,000m or so, though a special long range bullet of optimum shape can improve it.
The problem for most armies however is that their standard 308s are accurate and effective to 800-900m or so, and a decent rifle costs $5-$8 thousands dollars and weighs about 6-7kgs. The other weapons they commonly have are 50 cal weapons that can weigh from 12-15kgs that have effective ranges up to 2km or more but as well as being heavy are very expensive... often $20-$25 thousand dollars.
The 338 LM round in its original form was optimised for the 1,000-1,200m range in a rifle that weighs 8-10kgs and costs $10-$12 thousand dollars.
It basically fills a gap in range performance and also in weight and cost.
If you want to shoot at vehicles or targets wearing body armour at max range then a 50 cal or even 57 cal can do the job, but if you want to just sit out of small arms fire range but not carry a rifle that weighs so much it needs two men to carry it then a 338LM fits that gap.
The new 338LM probably has an effective range of 1.5km so in many cases targets that would otherwise have required a heavy expensive 50 cal can be taken with a lighter cheaper rifle.
I've toyed with the idea that you could build a .308 bullpup sniper with a 30+ inch barrel to try and squeeze out as much velocity as possible so you wouldn't need a .300 magnum or .338 lapua, but I think there's only so much velocity you can squeeze out depending on the barrel length,powder, and bullet weight.