[gandalftb]

The 5.56 round is regaining a great deal of support from Marine field tests. The 6.5 has great knock-down power but its recoil makes it imperative to fire from the shoulder.

Close-quarter, forced entry, urban warfare makes that very difficult at times. The M4 carbine currently issued to Fire Team NCOs is highly manueverable and controllable with the 5.56, but not so rechambered for 6.5.

The flat-top M4 is also highly modular for a wide variety of sighting accessories. Hard to see it going away. SOF operators do generally prefer and trick-out the H&K.

The 5.56 will likely survive until caseless ammo is introduced.

[PugetSoundSoldier]

The 5.56 will also not over-penetrate in an urban/house setting which is critical when multiple teams are penetrating a building. The last thing you want is unseen cross-fire between teams, and if choosing between giving a bad guy a few layers of drywall for temporary protection (before he is flushed out and eliminated) and over-penetrating and killing a friendly, I’ll take the former any day.