Too bad many branches of the military don't want the XM8 at all.
Some of the problems with the XM8 (posted by troy at AR15.com, where several people have actually used the XM8)
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- barrels being too short, giving horrible terminal ballistics with M855
- for some reason, XM8 barrels give lower velocity than AR barrels, at all lengths
- no rail system, so none of the refined and proven accessories are compatible. HK wants to supply all accessories, which will all use a proprietary attachment system.
- magazines are plastic, and about 50% wider than AR mags. This means a 3-mag AR pouch barely holds 2 G36/XM8 mags.
- supplied optic is of low quality compared to current commercial offerings (i.e., AimPoint)
- the integrated flip-up iron sights are a joke. You won't be able to flip-up the front sight if the barrel is hot either.
- typically of all HK designs, the optic is mounted far too high.
- the design of the charging handle makes a low-mounted optic rail impossible.
- users will not be able to change ergo items like the pistol grip, front handguards, or stock.
- the selector is too high and out of reach, again, typically HK
- the XM8 is expected to serve as a light automatic rifle, using unreliable, fragile Beta C-mags (yeah, right!)
- the rifle feels overly bulky (and it is)
Good summary list. Thanks.