I have had a local lawyer set up a  trust for me but I have a few technical -not legal- questions I am hoping you folks can help with.

I'm building a 9mm pistol for now.  Once I get my stamp approved this will become an SBR.

1) I'm considering an 8" barrel.  What will be the overall length?  

2) Will any pistol buffer tube work for a 9mm build?

3) I know a specialized 9mm buffer spring/buffer are required.  Any recommendations on who makes parts that work reliably?

3) I'm considering just building the upper from parts since it seems so hard to find complete uppers especially with M-LOC hand-guards. Will I need to headspace this or do  the pistol parts just match?  I've watched some videos on 9mm builds and they didn't mention head spacing.

4) If building requires headspacing or is just too hard for the non-professional, can you recommend a complete upper (with bolt, etc) that works well?

Edit to add #5

5) Do you recommend using a Glock mag setup, or Colt mag?  Why?

Not trying to be pushy as I know I'm new here, but I need the length question asap as I need to get the forms filed as soon as I can.


Thank you in advance for any help you are able to give.

in addition to the excellent answers from Mav3rick... if you want a last round bolt hold open, the Colt/Uzi style mags are designed to operate an AR style catch... the Glock mags are designed to work with a pistol slide stop and typically need specifically designed upper to work with them, at additional expense... my New Frontier Armory complete lower was around $280.... the buffer/spring assembly matched well with their modular bolt... good ejection patter without and screwing with it... I built mine for USPSA pistol caliber carbine so has a 16" barrel

Thanks lasnyder. OP's questions were a lot of mine when I first set out to build my 9mm AR. I got a lot of help from the community here so I always strive to return the favor.

Nice, info I was looking for.

Just to add one more Q

Mav you said rifle buffer for the 9mm build, does that mean a1/a2 length or will the carbine tubes still be gtg with a 9mm buffer?

Most will use a standard carbine spring and a heavy 9mm specific (longer) buffer such as the one from spikes. You do NOT use a rifle length buffer/spring

Slash heavy buffers is another option however much more expensive.

Correct. I meant to say carbine.

The length of a 9mm barrel is about .5" shorter than stated typically.  An 8" barrel will come out to about 7.5" from the receiver.

+1
The 9mm barrel stick further in to the receiver compared to 5.56.