So I have a lower that I want to register but I have not yet decided what I want to build.
What do I put on form one re caliber and barrel length?

You say you have a lower already. Want to share what type it is? Make & Model?
Do you have an idea what you want?
Not to be a total D*, but if you don't know what you want to build, how are we supposed to tell you what information to put down?

If you meant it differently, you put the firearms intended caliber (typically what the firearm is already marked, if so) in box 4c and the intended barrel length in box 4e (must be <16" for an SBR).

its a spikes multi lower. just bought it as last "necessary" pre-new rule. may want to build 300 or 5.56. not sure what barrel length

You will need to decide the necessary caliber as "Multi" is no longer accepted.
You can register it for anything you want and just send the ATF a letter stating its configuration has been changed. If the change will be permanent.
IE: register a 12", 5.56. Get your stamp back, build a 7.5" 300blk and file the change.

The differences between 5.56 & 300blk are many so I'm wondering how you are stuck between the two.
If you already have a 5.56/.223, I'd say the decision for 300blk is easy, since you've already considered it.

You have to have a plan to submit a form 1. But you don't have to follow it exactly once you have the stamp. I just did a Spikes 300 Blackout 8.3" barrel and 29.25" OAL that reflects the slidefire stock and muzzle brake I will put on it.

The 300 blackout needs to get engraved on the lower so getting getting that right makes sense to me.

Once you have the stamp showing that lowers serial number and it's engraved, you are out of the danger zone, even if the upper on it is a different spec. Some say you should notify ATF of the changes or have the parts around to build the original spec, but I don't think it is any legal requirement.

oh the Joy,
thank you for your responses. as always everyone is very helpful

I know that trust name and city state as manufacturer have to on the receiver. can you point out where it lists cal. must be put on as well. (in ref to sbr build, not firearm build) I would like to see the language.

27 CFR 479.102

Q: How must firearms be identified?

You, as a manufacturer, importer, or maker of a firearm, must legibly identify the firearm as follows:
By engraving, casting, stamping (impressing), or otherwise conspicuously placing or causing to be engraved, cast, stamped (impressed) or placed on the frame or receiver thereof an individual serial number. The serial number must be placed in a manner not susceptible of being readily obliterated, altered, or removed, and must not duplicate any serial number placed by you on any other firearm. For firearms manufactured, imported, or made on and after January 30, 2002, the engraving, casting, or stamping (impressing) of the serial number must be to a minimum depth of .003 inch and in a print size no smaller than 1/16 inch; and

By engraving, casting, stamping (impressing), or otherwise conspicuously placing or causing to be engraved, cast, stamped (impressed), or placed on the frame, receiver, or barrel thereof certain additional information. This information must be placed in a manner not susceptible of being readily obliterated, altered or removed. For firearms manufactured, imported, or made on and after January 30, 2002, the engraving, casting, or stamping (impressing) of this information must be to a minimum depth of .003 inch. The additional information includes:

The model, if such designation has been made;

The caliber or gauge;

Your name (or recognized abbreviation) and also, when applicable, the same of the foreign manufacturer or maker;

In the case of a domestically made firearm, the city and State (or recognized abbreviation thereof) where you as the manufacturer maintain your place of business, or where you, as the maker, made the firearm; and

In the case of an imported firearm, the name of the country in which it was manufactured and the city and State (or recognized abbreviation thereof) where you as the importer maintain your place of business. For additional requirements relating to imported firearms, see Customs regulations at 19 CFR part 134.

The depth of all markings required by this section will be measured from the flat surface of the metal and not the peaks or ridges. The height of serial numbers required by paragraph (a)(1) of this section will be measured as the distance between the latitudinal ends of the character impression bottoms (bases).

The Director may authorize other means of identification upon receipt of a letter application from you, submitted in duplicate, showing that such other identification is reasonable and will not hinder the effective administration of this part.

In the case of a destructive device, the Director may authorize other means of identifying that weapon upon receipt of a letter application from you, submitted in duplicate, showing that engraving, casting, or stamping (impressing) such a weapon would be dangerous or impracticable.

A firearm frame or receiver that is not a component part of a complete weapon at the time it is sold, shipped, or otherwise disposed of by you must be identified as required by this section.



Any part defined as a machine gun, muffler, or silencer for the purposes of this part that is not a component part of a complete firearm at the time it is sold, shipped, or otherwise disposed of by you must be identified as required by this section.

The Director may authorize other means of identification of parts defined as machine guns other than frames or receivers and parts defined as mufflers or silencers upon receipt of a letter application from you, submitted in duplicate, showing that such other identification is reasonable and will not hinder the effective administration of this part.

CanOfWhooppass wrote:You have to have a plan to submit a form 1. But you don't have to follow it exactly once you have the stamp. I just did a Spikes 300 Blackout 8.3" barrel and 29.25" OAL that reflects the slidefire stock and muzzle brake I will put on it.

The 300 blackout needs to get engraved on the lower so getting getting that right makes sense to me.

Once you have the stamp showing that lowers serial number and it's engraved, you are out of the danger zone, even if the upper on it is a different spec. Some say you should notify ATF of the changes or have the parts around to build the original spec, but I don't think it is any legal requirement.

It isn't an sbr until assembled as such. ATF is to be notified of any permanent change I wouldn't even mark the caliber until the first upper is built if at all. The caliber is generally on the barrel. Just make sure it's visible. Hell some people think it's ok to not mark lowers at all. The serial is on the lower and the serial is on your paperwork after all. I'm not in that camp but I can see the reasoning.

Even if I don't build the 300 Blackout upper, I need to engrave the lower because the main reason I'm doing this is to have a slidefire stocked lower to put on my already stamped 5.56 10.3" SBR. Just want to be able switch lowers, so I need 2 stamps.

I've always considered a 300 blackout upper for the stamped lower I already have in 5.56. That lower is a nice reliable non slidefire setup. The slidefire lower is just a range toy, too expensive to feed with 300 blackout, and bumpfire sometime has hammer follow bolt down for weak primer strike and no boom.

I'm really going to have one SBR with a spare lower for bumpfire and spare upper for subsonic blackout, so the paperwork should match.

First, do you have any short uppers now (ie. other SBRs or pistols)?

If so the easiest way to do this is to submit the form1 to build a new SBR with a currently owned upper - fill the form out to those specs.

Get form back, slap everything together and tada - a SBR. You can then feel free to change the configuration anytime and be GTG

As far as the engraving goes, the initial engraving is required. If the lower is marked multi you would need to engrave caliber as well as name and location - unless the caliber is marked on your barrel.