If by SCOTUS you mean Trump, then he did say it was okay.

in 2015 Defense Distributed sued the government for the right to sell their blueprints for their 3d printable guns. They lost in the federal courts and their appeal failed under the ruling that it was a violation of current firearm export laws.

In 2018 the Trump administration settled with Defense Distributed and allowed them to share their blueprints as well as giving them $40,000 in compensation for previous legal fees. Side note: The founder of Defense Distributed left 3 months after the payment and was then arrested in Taiwan after having sex with an underage minor in Texas.

in 2019 the attorney general filed a lawsuit against the Trump administration and the federal courts reversed the Trump decision once again making it illegal to share files without a license.

As far as I am aware, I am not aware of any changes since then.

If you want to read it, here is the legislation that explicitly states online posting of plans for 3D-printed firearms requires a license under the Export Administration Regulations issued by the Bureau of Industry and Security. Note the section where it says ANY file in ANY format is included in the legislation and that you can receive up to 20 years imprisonment and $1 million in fines.

https://www.bis.doc.gov/index.php/documents/policy-guidance/2572-faqs-for-the-commerce-category-i-iii-firearms-rule-posted-on-bis-website-7-7-20/file

Because you probably won't read all 69 (nice) pages here relevant information under the section of "3D Printing of Firearms"

Under section 734.7(c), such “technology” or “software” may not be posted on the Internet without authorization from the Department of Commerce’s Bureau of Industry and Security (BIS).

Q.34: I am planning to post technology or software that meets the criteria in section 734.7(c). Do I require a license or other prior approval from BIS before posting the “technology” or “software” on the Internet?

A.34: Yes, a BIS license is required under the Export Administration Regulations (EAR) prior to posting on the Internet of “technology” or “software” that meets the criteria under section 734.7(c). No EAR license exceptions are available for such postings.

Q.35: I understand that section 734.7(c) applies to Computer Aided Manufacturing (CAM) files, such as in G-code or AMF format, as executable code to produce the items described in paragraph (c). However, can you confirm whether the criteria in section 734.7(c) would also to apply to Computer Aided Design (CAD) files?

A.35: Section 734.7(c) covers “technology” and “software” for the production of a firearm frame or receiver or complete firearm, controlled under ECCN 0A501, that is made available by posting on the Internet in an electronic format, such as AMF or G-code, and is ready for insertion into a computer numerically controlled machine tool, additive manufacturing equipment, or any other equipment that makes use of the ‘‘software’’ or ‘‘technology’’ to produce the firearm frame or receiver or complete firearm. Any file meeting that criteria is covered regardless of name, including CAD files. Moreover, this includes any file, including any CAD file, that can be processed by a software program into an electronic format, such as a CAM file, with no or minimal additional information or manipulation from the operator(s), and that the file once converted will be in an executable code for the production of a firearm frame or receiver or complete firearm.

Q.36: If I do not obtain a BIS license prior to posting “technology” or “software” that meets the criteria in section 734.7(c), will I be subject to penalties under the EAR? A.36: Yes. This would be a violation of the EAR and may result in significant administrative and criminal penalties under the EAR. Under the Export Control Reform Act of 2018, criminal penalties can reach 20 years imprisonment and $1 million per violation. Administrative monetary penalties can reach $308,901 per violation (subject to adjustment in accordance with U.S. law, e.g., the Federal Civil Penalties Inflation Adjustment Act Improvements Act of 2015 (Pub. L. 114 -74, sec. 701)) or twice the value of the transaction, whichever is greater. Violations of the EAR may also lead to the denial of certain export privileges, potentially for a lengthy period of time.

In America you MIGHT need to show ID for age verification purposes in most states when purchasing gunpowder.

There is no country wide law requiring a permit to purchase everything you need to make bullets.

The exception might be buying a large amount(like 50lbs) but low pounds(<10lbs) is legal without a permit.

If 50 pounds or less of commercially manufactured black powder is being purchased, and the powder is intended to be used solely for sporting, recreational, or cultural purposes in antique firearms as defined in 18 U.S.C. 921(a)(16) or in antique devices exempt from the term "destructive device" in 18 U.S.C. 921(a)(4), no form is required. However, if the black powder is being purchased for any other purpose (regardless of quantity), the purchaser or other transferee must possess a federal explosives license or permit.

[18 U.S.C. 845(a)(5); 18 U.S.C. 926(c); 27 CFR 555.141(b), 555.26(a)]