G.Bl.P: Gewehr Blattchen Pulver== Rifle Flake Powder ( Blattchen means “little flat item”)…hence the Latin name for Cockroach “Blatta/ae”.
G.R.P. or simply R.P; Rohren Pulver (Tubular Powder “Rohr” ==Tube)
St.P. Stabchen Pulver: Punched disc powder (used in Pistol cartridges and Blanks)
It seems that 1940 was the culmination of German attempts to make US style Tubular NC Powder, for use in Aircraft MGs (more reliable at high altitudes, and more progressive burning). Hence the "Sonder-Pulver(Special Powder)…Sonder(special) as in “SonderKommando” of the Death camps.