See the link:
https://www.atf.gov/firearms/docs/rulemaking/final-rule-2021r-05f-definition-frame-or-receiver-and-identification/download

The § 478.12 Definition of Frame or Receiver starts on page 324.

Scanned through it quickly.
Does this mean it will still be fine to have for example spare parts like a BCM upper and extra BCG?

i cant concentrate enough  my brain is spinning after the first hundred pages.  

ill read it better tomorrow.

Sweet Jesus...it takes THAT many pages to "clarify" things??????  No wonder the government can't get anything done.

It does not apply to you nor parts

Pistol

How is that not a firing pin spring, making a Glock slide the receiver?
The only spring not inside the slide is the trigger spring. That's not a "primary energized component" as it's not even necessary for function.

Rifle

How is this not an AR15 upper receiver?

Also, I find it extremely odd that in all the given rifle examples (10 of them) the AR15 isn't used. It's easily the most popular rifle in the entire country. By design?

1. The striker sear is in the frame, so the definition applies.

2. The regulation specifically states that AR15-pattern rifles are exempt and grandfathered in. The regulation applies to future determinations.

For #1, it's all in how you read it:



That's a sear. This definition actually makes sense.

As for #2, ATF gonna ATF.

Keep reading. They explain (among a number of firearms) Glocks and AR-15's. From page 325, 326 and 331:

"(4) The following are nonexclusive examples that illustrate the above definitions:
....
(iii) Glock variant striker-fired semiautomatic pistols: The frame is the lower portion of the pistol, or grip, that provides housing for the sear."

....

"The following is a nonexclusive list of such weapons and the specific part determined by the Director to be the firearm frame or receiver as they existed on that date:
(i) AR-15/M-16 variant firearms: The receiver is the lower part of the weapon that provides housing for the trigger mechanism and hammer (i.e., lower receiver)."

Also in the PDF the ATF states the AR-15 is one of the most popular firearms in this country. From page 5.

"In the past few years, some courts have treated the regulatory definition of “firearm frame or receiver” as inflexible when applied to the lower portion of the AR-15-type rifle, one of the most popular firearms in the United States."

@sbhaven
That's irrelevant of my point.
None of their shit makes sense and contradicts another phrase/clause, just like most of the other gun laws.

Just hoping for some positive outcomes, with future lawsuits.

No its no irrelevant. They explicitly name Glock and explain which part is the frame (not the slide) because it holds the sear. They explicitly grandfather the AR-15 by saying the lower is the receiver/frame.

And yes the entire PDF is confusing as hell. They use a number of existing firearms as examples, and those examples may not follow the new rules they detail in the PDF. Its new designs that are going to be the issue and where the confusion really starts over what is the receiver/frame and what has to be serialized.