C&R · II · 573

M1911A1, Union Switch & Signal prototype

Section II: curio or relic, still subject to the Gun Control Act

Official wording

ATF P 5300.11 · APRIL 2025 EDITION · SECTION II · VERBATIM · PDF P. 19 ↗

Union Switch and Signal Company, Model 1911-A1, cal. .45, pistol, prototype model, with S/Ns US & S Exp. 1 to US & S Exp. 100.

ATF lists cal. .45; this is the .45 ACP cartridge.

ATF REQUIRESYour serial number is one ATF listsATF: “with S/Ns US & S Exp. 1 to US & S Exp. 100”
INFOATF states no date; production was about 1943.

Country: United StatesBasis: no citation
Manufacturer: Union Switch & Signal Co., Swissvale, PABasis: the ATF wording
Type: PistolBasis: the ATF wording
Action: Semi-autoBasis: no citation
Caliber: .45 ACPBasis: the ATF wording
Made: 1943production; ATF states no dateBasis: outside reference ¹
Service: Military

Official wording

ATF P 5300.11, April 2025 edition · Section II · PDF p. 19 ↗ · ATF original ↗

Entries

1 line

Verbatim check

Checked against the PDF text before every release

Editorial facts

Confidence: Medium · Last revised 18 October 2026 (Evidence pass) · How we rate confidence

References

1. oldcolt.com ↗, years: US&S M1911A1 'EXP No 1', Year: 1943; 'one of the approximate 100 "EXP" or "Experimental" Series pistols'

Fact tags

ATF the ATF wording states it.
REF ¹ an outside reference supports it; the number points to the list of references.
ESTIMATE an approximate or indirect reading, for example the production range of the base model.
NO CITATION we haven’t attached a reference for this fact; it’s our editorial reading, not ATF’s.

Source checked

20 October 2026: ATF’s page still lists the April 2025 edition

Corrections

None

Image: Wikimedia Commons, “M1911 and M1911A1 pistols.JPG” by Dkamm at English Wikipedia, Public domain. Retrieved October 2026.

Summary: Wikipedia, “M1911 pistol”. Text CC BY-SA 4.0.

The Colt M1911 is a single-action, recoil-operated, semi-automatic pistol chambered primarily for the .45 ACP cartridge.