The Czar's Army - how to find records #russia #records


I am new to this group and this is my first post.
I am researching my great-grandfather, Lejzer Glogowski, who was born in 1865 in Bialystok.  He emigrated to the U.S. in 1920.
While he was living in Bialystok he served in the "Czar's army."  He stated that he was a guard for the Czar and his role was sharpshooter.  Given his age it's feasible for him to have served during the reigns of Alexander III and Nicholas II.
I am wondering if there might be records that document his service, whether they be official government records, or something else that would be relevant.
I have searched the JRI-Poland indexes but have not found anything about his service on my own.
Any suggestions or help is appreciated.
Thank you.
Mitchel Kadish