5.56mm SBR - Is 8 Inches the New 10-Inch Barrel

[drummer]

In my opinion, there is a small window of operational viability for sub-10" 556 carbines for very specific, professional use. That use is executive protection where a very compact weapon is sought that won't be used suppressed. When compared to non-556 PDW alternatives, an 8" 556 with modern duty ammunition provides increased terminal effectiveness while simplifying training and logistics for agencies already heavily invested in 556 AR variants. 8" is not the new 10". But frankly, the quality of the modern duty ammo is such that it still performs relatively well from shorter than normal barrels. 10-11" barrels are still the way to go for CQB or patrol operations.

300 BO is a better choice for sub-10" carbines. However, I've not seen terminal ballistic results for ANY load that doesn't penetrate more than the recommended amount; some are much more. If LE was pursuing the 300 BO more fervently, maybe the major manufacturers would make better LE loads. At this time, it's a civilian chambering. For my personal use, I'd take a 9" 300 BO over an 8" AR any day but I can't recommend 300 BO for LE at this time, with the caveat that there may be some new loads/ data that I haven't seen.

Weapon reliability is another concern. There is no free lunch. Increased bolt carrier velocity brings about reduced reliability and parts life.

[Unobtanium]

This issue of extremely short barreled 5.56 rifles came up on another forum because a prominent online vendor was touting the new B&T APC556 which has a 8.7" barrel. I pointed out the fact that 5.56 rifles with barrels less than 10 inches have a very limited performance profile as most loads will not reliably expand past 50 yards or so. This vender disagreed and cited data from Black Hills that their 62 grain TSX will perform well out to 150 yards when fired from an 8" barrels. He also postulated that several other bonded loads from Speer/Federal would also do well from an 8" barrel out to 100-150 yards.

This all seemed a bit odd to me as this would mean that I may need to reset my parameters for barrel lengths if 8.7" guns in 5.56 are now legit 100-150 yard weapons. I wanted to check in here with people in the know before dismissing these claims as a guy trying to market a gun that he was selling.

Personally, I have no use for a 5.56 rifle that has a barrel less than 10". I do own a couple of 300 blk guns that have 8-9" barrels. If I need something even more compact (sub-20" overall length), it is going to be a MP5K.

The vendor is accurate in his assessment. I remain a 14.5"+ fan, though.