Building a .300 blackout pistol. Going to use a pistol buffer tube, and a 10" barrel. I think the OAL will be 26-26.5"?

Is there a maximum length I can build a pistol legally?

I have a 5.56 build with a 10.5 and a PSA pistol tube, OAL without pinning my FH is just shy of 26, so it cannot have a vert grip.

State laws may very, but I believe that fed law says that as long as it does not have a shoulder stock you are GTG.

I love the look of my 10.5 5.56, is there a reason for the 10" barrel? I thought I had read somewhere that .300 BLK burned all of its powder in 8" and after that, MV increases were minimal

It's a 10.5" barrel only because that's all I could get to put it together at the time. Will eventually source an 8" barrel for it but like you said I love the look/size of it with a 10.5".

I had read some stuff about 26.5" and being considered a "firearm". Just wanting to make sure I was not going to be doing anything wrong or making a gun that required a stamp somehow...

You're fine federally at any OAL length (or any barrel length). I believe MI is the only state that may still have some oddity with a pistol being 26" or more, though some others do have a barrel length maximum in their statute definitions. (TN is "under 12 inches" for example).

The only reason you hear so much about it is that lately is that a relatively new ATF ruling allows a handgun of 26" or more in legal OAL to also have a vertical forward grip attached. That's when it becomes a legal "firearm" -- remove the VFG and it's a handgun again. (note that muzzle device doesn't count in OAL unless permanently attached).

Federal definitions have not changed, this is merely an interpretative exception to what is otherwise AOW classification.

- OS

+1

Federally, there is no OAL limit on a handgun, but if it happens to be over 26" OAL, you can attach a VFG, and it becomes a "firearm" instead of a regulated "AOW"

I built a 30" pistol a few months ago, it was only a pistol for a few minutes though.

This for all my builds.  My 20" M16ish repro was a pistol first too.

I have got a 10.5 inch pistol with the KAK super tube and extra lop kit installed. over all legal  length exceeds 26 inches. looks like i can put a vertical fore grip on it, legally. however, my lower is an  RRA marked "Pistol Only". would this alter the status of the weapon, in regards the VFG?

Nope. what is marked on the receiver is irrelevant to it's actual usage.

one other question. still a little unclear after reading the ATF documents.

if i attach the 10.5 inch pistol  upper with a vertical fore grip attached  to a lower that was originally a RIFLE lower, but has the KAK super buffer tube and Sig brace, making the overall length greater than 26 inches, is this also legal?  the part i am hung up on is that the lower was originally a  rifle lower and still is.

If it started out as a rifle, you cannot make it anything but a rifle without a stamp from the ATF.  Stupid rules, but it is the govt after all.

Even with a tax stamp, it could never be a handgun. Would have to be an SBR that you used without a stock. :)

- OS

thanks guys, after reading the rules again, no doubt you are correct. i will keep that upper on a lower that was never anything but a pistol lower.