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Assuming that means a 1911 in .45 ACP, no. .45 Long Colt also known as just .45 Colt is a rimmed cartridge that is not interchangeable with .45 ACP.

Hi Fred and welcome. No. 1991 uses 45ACP which is a rimless cartridge, and the Big Boy uses 45 Long Colt which is a rimmed cartridge. Difference pictured here: https://www.reddit.com/media?url=https%3A%2F%2Fpreview.redd.it%2Flearned-a-lesson-today-45-colt-is-not-the-same-as-45-acp-v0-p0h36y631u5d1.jpeg%3Fwidth%3D314%26format%3Dpjpg%26auto%3Dwebp%26s%3Db58bc61b9f9225c4c8bf83aaf3fa379b124fdfb6

No, the Big Boy is chambered for .45 Long Colt which is a rimmed cartridge. The .45 ACP is a rimless cartridge. Not interchangeable.