I'm asking because Pete Pig now has their resculpted dismounted cav packs available.What hat was standard issue for the Union?
At the scale you are working on, it doesn't really matter whether you are using "federal" or "confederate" figures. Use the ones you like and paint them appropriately.
By regulation in the Federal army, each trooper (indeed, every soldier) was issued with both a dress hat and a forage cap. Likewise, he was issued with both a dress coat and a fatigue coat. The dress hat was the "Hardee" patterm, which, when issued, looked like an old Pilgrim hat from the 17th century, sans band and buckle. It was to be worh with the dress jacket for dress occasions.
He was also issued with a cap and "sack coat", which were to be worn on occasions of fatihue duty and when in the field. That this was the standard followed can be seen by large numbers of images of US Regular troops in the field, all wearing sack coats and forage caps.
Keeping this all in mind, who wore what decidely comes down to a unit/place/time affair. Some units never got the dress hat. Some units, like the "Iron Brigade" chose to wear the hat exclusively.
As a general rule, absent any documentation, you can paint the Federals in caps and coats, But like I say, it's a general thing, and not wholly accurate for any of the theatres, Eastern or Western.
As to Confederates, there were many CS regiments who used forage caps, some who used hats, and a lot with mixed head gear. You have to keep in mind that the CS uniform regulations were patterned upon those of the US Army, with colour and decorative/insignia changes. The general pattern of the equipment and clothing, however, mirrored that of the Federals. Short jackets, caps, almost identical accoutrements. Again, it's very much a unit/place/time call as to who wore what.
When painting cavalry, I have almost always used whatever figures I liked, without consideration of the nomenclature except for what they were armed with, and painted them appropriately for whatever unit I was building.
respects,