[yarddog]

All AR type rifles tend to be accurate regarless of barrel length.

I once did some casual testing between an 18 inch barrel .308 (a Remington 788) and a regular HBar in .223.

I was shooting surplus .308 and some of the new 68 grain .223. Up close they both penetrated an old syrup cooker. At longer ranges, to my surprise the .308 did not penetrate while the .223 did.

[snuffy smiff]

I'd be very interested in the chrony results of that test.

finally it seems the Army is waking up to the fact that them pea-shooters just ain't gettin' 'er done!(found at mausercentral):

http://www.freerepublic.com/focus/f-news/1430038/posts