Hello Walter,
Without any picture it is not so easy to identify:
G.d.C.8.20. Garde du Corps, 8. Escadron, Waffe no.20
The dotted out unit mark:
I think the C should be a G.
4.G.A.r.2.113. Garde Feldartillerie-Regiment no.4, 2.reitende Batterie, Waffe 113
This regiment was stationed in Potsdam.
The Garde units received always as first new guns and equipment. The year 1881 and the low serial number indicate it.
Regarding your M/1883 I recommend to use a magnifying glass to complete the missing letters and numbers.
On your holster the marking is F.A.R. Feldartillerie- Regiment.
Both revolvers will have the stamps of the final Prussian inspection: 1. Gothic letter with crown (marking of the responsible inspector)and 2. the bigger superviser marking FR with crown.
On the left side of the barrel and on rear face of the cylinder should be an eagle stamp, signifying the successful Prussian proof.