I want to SBR a AR-15 pistol. I live in Virginia..... What do I need to do ???

First, you might want to ask in the VA Hometown Forum since I don't know what the laws are there.

https://www.ar15.com/forums/Hometown/Virginia/24/

If they're kosher there, file the appropriate Federal paperwork.

https://www.ar15.com/forums/Armory/General-NFA-Questions/17/

There are no VA restrictions...yet. Fill out the Federal Form 1, submit passport photos and fingerprint cards, pay your $200 and wait for your stamp.

It's pretty straight forward.  Use ATF E-forms to complete a form 1 submission.  You will attach a passport like photo to the submission - if you don't take your own, CVS will do it, just get the emailed image in addition to the paper photo.  You'll pay the $200 tax when you submit the form.  Within a short period of time of your submission, you will get a confirmation from the ATF that it was received, you need to mail that confirmation along with 2 finger print cards to the ATF processing office in West Virginia.  Once it is approved, you need to get the lower engraved with your name, and location i.e. Harrisonburg, VA in my case.  If your lower doesn't specify the caliber, and the barrel doesn't clearly indicate it either, have the engraver mark it 5.56 mm.  Once the form is approved, mail a copy of it to your local chief law enforcement officer.  Once you've done these steps, you are clear to add a rifle stock in place of whatever your pistol receiver extension is.  Keep in mind that with an SBR, before you cross state lines with it as an SBR, you need to notify the ATF, and get their approval for it.  It's a form you submit, and you can submit them for a 1 year period at a time to go to a specific state.  
PM me if you have further questions.  While it sounds complex, it's actually pretty easy.

Thanks GUYS !!! I have a couple PSA .300 Blackout pistols I want to SBR. Can I submit paperwork for both of them at the same time ? Where do I get fingerprint cards done ? I am afraid to go out too much due to my age and fears of Covid-19.

Here in Texas, I went to the sheriff's office/jail and got mine done free. They even supplied the correct finger print cards.

You can do multiple line item requests on one eFile form 1 submission (I think anyway.) They'll still need a $200 tax stamp per item.

You can request blank FP cards direct from the ATF (for free.) Here: ATF FP card request

Order "FBI FD-258LE - NFA, Imports ORI WVATF0800" from the drop down menu.

Get yourself an ink pad and roll your owns prints. I've done it 4 times without issue. I mail mine via USPS priority mail when ready.

Check out YouTube. A few videos will show exactly what to do and how to fill out the Efile form 1 on ATF website. Double check your information before you submit or they will deny you, refund your money, and you have to restart and get to the end of the line (I speak from experience). $200 tax stamp for each item. You can upload a photo (passport style) on their site. I stood infront of a white wall and had my wife take a headshot on a phone camera. Once you submit, you'll get email confirmation with a doc to snail mail in your fingerprint cards. Again, follow their instructions exactly and you'll be fine. Turnaround for e-filing is around 3 to 4 weeks, ymmv.

I work for a police department so fingerprints are free, but we typically charge $10 to $15 per 2 cards. Just call up your local PD and make an appointment. Some PDs will have set windows for civilians/residents. You'll need 2 fingerprint cards PER NFA item. 2 potential SBRs will require 2 different efilings and 4 fingerprint cards (2 per item).

Our PD is in phase 0/1 for covid right now, so we have heavy restrictions. Im sure most other agencies are as well and will adhere to covid safety (masks, gloved officers/detectives, etc). Again just give your local PD a call and they'll be happy to give you the info.

Also, the ATF website sucks and runs off of AOL dialup so be patient and be prepared for it to be down at time.

Not a requirement, but one thing to consider is if you want to establish an NFA trust ahead of time.  Myself and many Virginia forum members can attest to the great services that John Pierce provides.  His website is a great resource and has the best deal around for establishing an NFA trust.
www.johnpierceesq.com

A big +1 for John Pierce if you need/want a NFA trust.

If you are in the Charlottesville area, Albemarle County Firearms on W. Rio Rd. has the FBI fingerprint cards.

Have fun,
Bob S.

Went to the Stafford Sheriffs Dept and got 12 fingerprint cards done. They scanned mine in and printed them out. In and out in 15 mins.

OP,
Something to consider is the wait time, you’re gonna potentially need a lot of patience.
I thought maybe six weeks for an efiled form 1....nope, frikkin “submitted-in process” since the middle of July ??
FBI is allegedly waaayy backed up on background checks.
YRMV

Lots of good info here:
https://www.ar15.com/forums/Armory/General-NFA-Questions/17/

I do Form 1's on ATF's eForms with a Trust, and consistently get the approvals in about 4 weeks.  You can order FP cards from ATF and roll your own.  CLEO notification goes to VSP Superintendent.  

I do a separate Form 1 eForms for each firearm.  I find eForms performs best early in the morning (~8 am).  It seems to slow down later in the day to the point of being frustrating to use.

Do you need finger prints cards if you’re using the Trust route?

Yes.

The BATFE changed that a couple of years ago. Now, every trustee that can have access to the items in the trust, must provide Photo's & Finger Prints.

According to them, they were closing the "Loophole" that a Felon could be added to a trust and gain access to firearms. Of course it didn't matter to them that if a Felon did get access to a firearm it was already another felony...

Enjoy the snow!
Bob S.

Time to play "The Washington Post March."

You will recognize it instantly.
Washington Post March