Dear Ms. Simmons,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located the series Enlistment Papers, 1798 - October 31, 1912 and Registers of Enlistments in the United States Army, 1798 - 1914 (M233) in the Records of the Adjutant General's Office, 1762 - 1917 (Record Group 94) that include military service files of the Regular Army. These records are not digitized. For access to the papers and M233, please contact the National Archives at Washington, DC - Textual Reference (RDT1) via email at firstname.lastname@example.org.
We also located 10 series in the Records of U.S. Regular Army Mobile Units (Record Group 391) that pertain to the 6th Cavalry Regiment from 1903 to 1912. These records are not digitized. For access to these series, please contact RDT1.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RDT1. We apologize for this inconvenience and appreciate your understanding and patience.
The Registers of Enlistments have been microfilmed as Microfilm Publication M233 “Register of Enlistments in the U.S. Army, 1798-1914” that has been digitized and is available on Fold3 as Army Register of Enlistments, 1798-1914; on Ancestry as U.S. Army, Register of Enlistments, 1798-1914; and on FamilySearch as United States Registers of Enlistments in the U.S. Army, 1798-1914.
We hope this is helpful. Best of luck with your family research!
Do you have any additional information on your grandfather such as a name, DOB, place of birth. Any additional information could help.