^^^^ This is where a little bit of information can be dangerous.
The latter statement is TRUE, but:
Q5. I’m a nonimmigrant alien lawfully present in the United States without a visa. May I purchase or possess a firearm in the United States?
A5. A nonimmigrant alien who is lawfully admitted to the United States without a visa (e.g. Visa Waiver Program), may acquire or possess a firearm in the United States, provided that he or she is not prohibited from shipping, transporting, receiving, or possessing firearms or ammunition in the U.S.
In addition, a nonimmigrant alien legally in the United States with or without a nonimmigrant visa may lawfully acquire a firearm
only if he/she meets State of residence requirements as required by the Federal government.
These requirements are irrespective of the licensed status of the individual from whom the alien is purchasing the firearm. An unlicensed individual is prohibited from selling a firearm to an
out-of-State resident. A Federal firearms licensee (FFL) is prohibited, with few exceptions, from transferring a firearm to an
out-of-State resident.
So while it's possible if you meet "residency requirements", that doesn't apply if you go down "for the day or a couple weeks for a holiday".
The above applied to myself when I was serving on exchange duties with the US military (while serving in the Canadian military). I was "stationed" in the US for 24 months. I did NOT have a Visa but was issued an I-94 (Immigration record) and was a "resident" of a US State complete with drivers licence etc issued by that State - so the rule applied "during that period" - not now that I am no longer a "non-immigrant alien" who is NOT a State resident.
So you have to be careful when you read a simple answer...
https://www.atf.gov/resource-center/docs/non-immigrant-alienspdf/download