Building a custom AR

[1911 Junkie]

Anything less than a 16" barrel will require you to have a tax stamp. $200 and a whole lot of waiting. You must have the stamp prior to getting the barrel. (Not that you "can't" get the short barrel, it would just be illegal)

FWIW shorter barrels in the AR platform are more prone to failures. They tend to be a lot more picky about the ammo used.

If you really want it, apply for the tax stamp. Don't let FQ scare you with stories of midnight visits from the ATF to check your weapon. 

[tombogan03884]

The $200 tax is for Machine guns and Suppressors, If I remember right  the tax on MB's Serbu Shorty 12 ga. was $5 as it is a different classification, (short barreled Shot guns are classed as "Any other weapon") I think, SBR's (short barreled rifles ) are the same $5
But you still have to do all the paperwork first.

[1911 Junkie]

The $200 tax is for Machine guns and Suppressors, If I remember right  the tax on MB's Serbu Shorty 12 ga. was $5 as it is a different classification, (short barreled Shot guns are classed as "Any other weapon") I think, SBR's (short barreled rifles ) are the same $5
But you still have to do all the paperwork first.

Nope. I have 2 friends that built SBR's. It is a class 3 weapon. $200 tax stamp.

[tombogan03884]

 OK, I wasn't sure, but I knew MB said the Serbu was only $5.

[1911 Junkie]

Quick search found this. I had never heard of the $5 tax before. Looks like you make some cool stuff for less money. 

Under the National Firearms Act (NFA) it is illegal for a private citizen to possess a sawed-off modern smokeless powder shotgun (a barrel length less than 18 in. or 46 cm and an overall length less than 26 inches) without a tax-stamped permit from the Bureau of Alcohol, Tobacco, Firearms and Explosives, which requires a background check and a $200.00 fee for every transfer.[1] (Short-barreled muzzleloading blackpowder shotguns, in contrast, are not illegal by federal law and require no tax-stamped permit, although they may be illegal under state law.) As with all NFA regulated firearms, a new tax stamp must be purchased before every transfer. Inter-state transfers must be facilitated through a Class III Federal Firearms Licensed (FFL) dealer while intrastate transfers may be between two persons.

Additional restrictions may apply in many other jurisdictions. State and local laws may entirely prohibit civilian possession of short-barrelled shotguns. (These restrictions do not apply to military and police departments.) In addition, some firearm types that would normally be considered to fall into the Short Barrel Shotgun (SBS) category are not legally considered to be a SBS. A shotgun is legally defined as a shoulder mounted firearm that fires shot. Shotguns and shotgun receivers that have never had a buttstock of any type installed are not shotguns, as they cannot be shoulder mounted. Therefore, cutting one of these below the 18" barrel and/or 26" overall length cannot produce a SBS as the firearm was never a shotgun. The Bureau of Alcohol, Tobacco, Firearms & Explosives recognizes these firearms as being a smooth bore handgun which is an Any Other Weapon (AOW). Unlike a SBS, an AOW only carries a $5.00 tax and can be moved interstate without Federal approval. However, to maintain its AOW status, one may generally not have a buttstock (making it a SBS) or a rifled slug barrel (making it a Destructive Device (DD) if the bore is over 0.5"). Both SBS and DD weapons require a $200 transfer tax and prior Federal approval to transport interstate.

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[Badgersmilk]

Maybe the least of your worries when building a whole new gun, but unless you have very small hands, I'd avoid the Hogue grip you mention.  I'd bought one (thats been laying in a "spare parts box" since day 1) and like the feel, but it's just to small to provide good support if I compare it to the factory grip that came on my DPMS, or even better, the G27 grip I use.  I've tried about every grip I've ever seen for AR's, and while it may not be the "tacticoolest", the CAA G27 wins hands down for comfort and having a good solid feel for me.