Armalite states my AR10A4 has a 16" barrel, but HPD registered it as an 18". When measured from the base of the slip ring to the tip of the flash suppressor (as HPD did) it is 18, and without the suppressor it's 16.....so which is it? 

I have a Colt M4 that colt states is a 16" model and measured the same way, it's 14 without the suppressor and 16 with......so are colt and armalite using two different landmarks to state their barrel lengths?  In other words, it looks like armalite EXCLUDES the suppressor in their official barrel length designation to state 16, while colt INCLUDES the suppressor to designate theirs a 16.

Anyone have input on this?  Because armalite and colt state my AR10 and M4 are 16" models, but the lengths are different when measured via the same landmarks by HPD.

This is the kind of crap that will end up creating a bunch of criminals out of law abiding citizens... WTFCares how long a barrel is?  Does it make it that much more dangerous?  All these stupid arbitrary rules governing cosmetic features is absolutly ridiculous.  We need to seriously hit the reset button soon.

Legally, barrels are measured from a closed breech inside the barrel to the end. If the flash supressor/brake a pinned and welded, it is added onto the barrel length. The way HPD measures is just an informal measurement, more of a guestimate. I wouldn't worry too much about the way HPD does it.

Thanks for the info.
I found info similar to yours that BATFE measures with a closed bolt and a rod down the barrel, marking the end of the suppressor/hider. 
I also found a discussion with an armalite armorer and he said armalite measures measures barrels from the closed bolt to the end of the barrel, but specifically excludes the suppressor.
I guess colt includes the suppressor and armalite doesn't. Funny that in an industry with such devoted connoisseurs there would be such a glaring discrepancy between the standard used by two top competitors for such a critical specification like barrel length! Doesn't make sense.

And as far as the laws about barrel length....just being a lowly subject of the 'state' I must concede that I should thank our Hawaii legislators for making my minimum barrel length 16" because I can't commit crime with such a barrel; I mean just imagine if I had say a 14" barrel on my rifle then I'd be able to go on killing sprees I could never engage in with my 16" barrel. Thank god Hawaii legislators are so much smarter than people like me. Just imagine what the rifle-related crime rate would be otherwise!

And as far as the laws about barrel length....just being a lowly subject of the 'state' I must concede that I should thank our Hawaii legislators for making my minimum barrel length 16" because I can't commit crime with such a barrel; I mean just imagine if I had say a 14" barrel on my rifle then I'd be able to go on killing sprees I could never engage in with my 16" barrel. Thank god Hawaii legislators are so much smarter than people like me. Just imagine what the rifle-related crime rate would be otherwise!

Just to clarify, the 14" regulation for long guns isn't really a Hawaii thing, it's a nationwide regulation. Most guns with 14" barrels would fall under the Short Barreled Rifle/Shotgun regulations and need to be registered with the BATFE as an NFA item. This is always a tricky regulation though as if the gun doesn't have a stock, it can be a pistol or "other" (as in the case of some Franklin Armory guns).

Aren't these laws fun?

Yeah, makes sense.  But you mean 16" right?  The minimum barrel for rifles in Hawaii is 16, right?

Yeah, makes sense.  But you mean 16" right?  The minimum barrel for rifles in Hawaii is 16, right?

2A was pointing out the fact that the 14" barrel length (you mentioned) is more of a Federal restriction (NFA). But yes, 16" is the minimum barrel length in Hawaii.

§134-8  Ownership, etc., of automatic firearms, silencers, etc., prohibited; penalties.  (a)  The manufacture, possession, sale, barter, trade, gift, transfer, or acquisition of any of the following is prohibited:  assault pistols, except as provided by section 134-4(e); automatic firearms; rifles with barrel lengths less than sixteen inches; shotguns with barrel lengths less than eighteen inches; cannons; mufflers, silencers, or devices for deadening or muffling the sound of discharged firearms; hand grenades, dynamite, blasting caps, bombs, or bombshells, or other explosives; or any type of ammunition or any projectile component thereof coated with teflon or any other similar coating designed primarily to enhance its capability to penetrate metal or pierce protective armor; and any type of ammunition or any projectile component thereof designed or intended to explode or segment upon impact with its target.

Got it.....thanks!