alright, i'm a little confused about the 16" bbl on an ar15. i know 16" is the minimum length before a SBR. now i've read that 16"  bbl after it is put into a reciever makes it 14.5" so pin a sepresser on and you'll be at 16". but this doesnt make sense to me becouse on other weapons you measure where the bbl starts, shotguns, bolts, BULLPUPS.. so no matter what as long as the bullet travels 16" it is legal...

can somebody streighten me out... it is true that 1.5" of the bbl is in the reciever right?

You measure the length of the barrel from the boltface, you're right about that.  The "regular" civilian barrel is 16" from the boltface WITHOUT the flashhider, since the flashhider is removable.  On a 14.5" barrel, the flashhider is pinned in place so it's permanent, becoming part of the barrel and therefore part of its length.  There's not an inch and a half of barrel anywhere in the receiver.

alright thanks, i found out what was confusing me...
http://www.spikestactical.com/z/index.php?main_page=product_info&cPath=26&products_id=122

Yeah, that's a .22lr upper, so they can back the barrel into the receiver a bit for looks.

As Eric802 said, the barrel length is measured from the inside, (as in you need a cleaning rod to measure it) from the face of the bolt (with the bolt closed/locked) to the muzzle end of the barrel.  Muzzle devices(flash supp, comp or brake) only count if they are permanently attatched. (pinned/welded etc.)

Since the amount of the barrel "contained" within the receiver(or trunion for AK's) doesn't change the barrel length according to the law, it doesn't matter.  The only exception is the overall-length requirement which is 26" minimum regardless of barrel length.  In practice however, this normally only effects bull-pups with a relatively short-length reciever.

Tex78