There are two possibilities on finding out how a regiment was equipped. The first is the Compiled Military Service Records (CMSRs) and the second is the Quarterly Ordnance Reports.
The CMSRs often have very valuable research material often overlooked or not analyzed at all. When you look at the CMSRs, look at the officers in the companies, the Field and Staff officers, the brigade officers and staff records. These records will often have issue and turn-in documents and I have found several quarterly ordnance reports too. The brigade officers and staff records can be found at the National Archives in Washington, D.C., Wallace State College in Hanceville, Alabama, or the Birmingham Public Library. I am not sure if the National Archives Annex in Atlanta has them on microfilm.
The original Quarterly Ordnance Reports that did survive can be found at the National Archives in Washington, D.C. Again, I do not know if the Annex in Atlanta has them available on microfilm.
As Mr. Lowe noted, as the war progressed and better weapons came into the inventory, companies and regiments would be issued better weapons so what they started out with it not likely what they had by mid-war and late-war.
I hope this helps in you search.
Gerald D. Hodge, Jr.
War Between the States Historian
Historian: 39th Georgia Infantry Regiment
Web Master: http://39thGAVOLINFRGT.homestead.com/39thHomepage.html