i just want to know the process of putting an 80% lower on a sbr form 1. im guessing that i have to make up my own model name/number and serial number ahead of time to put on the form 1, then once it gets its stamp, i go engrave the lower with: the serial # i made up; model name/# i made up, caliber, my trust's name, and my city/state. correct?

this is for my 14.5 pinned/welded 300blk im wanting to chop down now that i have a form 4 submitted for my suppressor (saker 762). I appreciate any and all advice/help ahead of time.

You've pretty much got it.  The serial number must contain at least one numeral.  You can engrave the barrel with the caliber, rather than the lower, if you prefer, but the caliber needs to be visible with the rifle assembled.  The city/state technically need to be where the SBR is made, which may or may not be the location on the Form 1, or your residence, or whatever.

Also, there's no need to wait to get the approved F1 before engraving.  There's no harm in waiting (other than that it delays your ability to shoot the SBR), but no need either.

thanks for the reply, i just wanted to get my ducks in a row first. and i kinda figured i could engrave beforehand but in the unfortunate case of my application being denied i dont want something permanent incase i change my mind on re-submitting for that lower.

now i see on guntrustlawyer.com on marking the cal/gauge they say
"4c  should contain the caliber or gage ( Multi is not acceptable, you can only list one, if you have additional calibers you want to list, you should attach additional configurations in a letter attached to your Form 1 stating the caliber, barrel length, and overall length as related to the firearm listed on the Form 1.)"
so i can not take a 5.56 sbr lower and put it on my 300blk upper? or i can have it registered as a 5.56 cal sbr lower and from time to time shoot an 8" 300blk upper on it?

Item 4c on the Form 1 should list the caliber you plan to initially build your SBR.  So, if you're going to build as 5.56, enter (only) 5.56 (don't enter 5.56x45).  If 300 BLK, enter 300 (with no leading decimal).  There is no need or benefit to attach a letter or other document detailing other configurations you may want to use.  This is distinct from the marking requirement.

An SBR must be "conspicuously marked" with its caliber.  That marking can be on the receiver or barrel (or, I think, a few other places; I don't recall what they would be though).  The marking needs to reflect the actual caliber.  So, if you're planning on a 5.56 build, you could engrave your lower with "CAL 5.56 MM", and you'd be fine without having anything on your barrel.  However, if you put a 300 BLK upper on it, it would need to have the caliber marked in a place that was visible without disassembling the gun.

ATF requests, but has no legal basis to require, that you notify them of any "permanent" change in configuration of a NFA weapon.  In the case of an AR, it's pretty hard to argue that anything is permanent, particularly when swapping uppers.

You can run whatever upper you want after the initial build/approval. Your paperwork should reflect whatever that initial build is, and then after that you can run whatever you want. My 80% lower was engraved 5.56mm, and that is what I initially built it as, but I also run a 9mm upper. You do not have to attach any paperwork with the Form1 stating that you are going to run some other caliber. I have seen it stated that ATF wants you to inform them if you make any permanent change.......but uppers are not permanent changes. (two push pins and you are back to whatever it was originally built as.

i get it now guys thanks!

I would include a note that you are SBR'ing a 80% lower.  That way they dont kick it back for your make and model not being in their system.  If possible finish the lower and marking and include a photo of the markings so there is no question about what is going on.

MAHA

Spend the big $50 and get a new lower with a serial number already on it.  Save the 80%er for a title I build.

I didn't do it on purpose, but I realized the other day that all my title i guns are 80%ers, and all of my title II guns are commercial.

There are reasons for wanting an 80% turned into a Title II firearm.  Here's my reason. This 80% lower normally carries a 607 upper. I'm working on a M4A1 clone lower too, to use with the CQBR upper that is in this pic.

Its not that i dont have the money to buy a commercial lower, i just enjoy building my own rifles and therefore have no interest in commercial lowers.

additionally if i were to get a commercial lower just to form 1 then i would have an 80%'er laying around un-used and i can not have that. the g/f already is dissappointed in my 3 builds since Jan. each of which was $1500+ (one of which is for her of course), plus my Saker 762 can in jail right now so building another rifle will leave me a single man. and im kind of fond of her

Looks like my options are to find a place that can locally do it while i physically wait for it to be finished.