If you make an AR that is greater than 26" do you still need a pistol stock? Can you use a vertical grip?

I thought that if the barrel was less than 16" than you needed a pistol stock and can Not use a vertical grip despite the overall length.  

The niche ruling is that the only thing different about a 26" handgun is that you may legally add a vertical forward grip, at which time it becomes a non-NFA "firearm" (as long as it's not concealed on the person).

Remove the VFG, it's a pistol again.

The rest of what you mention is SBR stuff, nothing has changed. Barrel of less than 16", no stock, and/or overall length of rifle including stock must be 26" minimum.

- OS

Yes it has to be made as a pistol if the barrel is less than 16", but there is no such thing as pistol stock. You can't add a stock without a stamp. 

An AR pistol with an overall length of 26+ inches becomes a "firearm" if you add a VFG. 

It is from the rear of the buffer tube, (not the end of the stabilizing brace) and to the end of the barrel  or the end of the muzzle device if it is permanently attached.

A flash can would only be counted in the barrel length if it is permanently attached. Rails are not counted in OAL as far as I know.  

The length is measured from the end of the buffer tube to the end of the barrel. To count to the end of muzzle device but it must be permanently attached to the barrel in one of the ways described by the ATF as permanent. (silver solder, full weld, or pin and weld)

The shockwave brace is not a stock and therefore it is not legal to measure from the end of the brace. I don't think the rail counts either as it can be removed in most cases, and the pistol would still be able to fire.

Only the end of the barrel has ever been cited by ATF as counting in the OAL on the forward end of a firearm. And as you mention,  only a permanently attached (as per ATF stated methods) muzzle device becomes legally part of the barrel.

- OS

And, to reinforce it, if you have a pistol with OAL longer than 26" and then add the VFG - it's no longer a pistol. You cannot treat it like a pistol in transport or use, either. It's a firearm - not a pistol - not CCW legal. Many states would then treat it like a rifle to be stored in the back of a vehicle unloaded and cased.

I wouldn't treat that distinction as casually as some do posting here. Pistols are legal under CCW law to be loaded concealed close to hand. Not "firearms." It's going to be a tough enough sale if a traffic stop is involved anyway. I built mine no brace no rails under 26" and lose no sleep over it. Those extra enhancements aren't capable of doing much when you consider the range and target sizes involved.

AND FWIW while vertical 'broomhandle' type grips are classified as VFGs, angled grips like the Magpul AFG, Mako/Fab Defense PTK foregrip and Stark Express are all OK. The Express has the most steep rake at 45 degrees and Stark has posted their ATF acceptance letter for pistol use. So if you don't want to mess around with a tape measure & state laws there are a lot of great grips out there not considered VFGs.