I used to need a dibber to seat Hobbys or Gecos in the Umarex magazines. The Hobbys have very oversize skirts. Now I size all my pellets with a sizer from UKNeil and load the Umarex with the ball of my thumb. Velocity is more consistent too, with the sized pellets of both types.
The only comment I have about Gecos, apart from the fact that they are good pellets, is that they are a few thou shorter than Hobby and manage to drop through my H & N Matchbox, jamming the tray! It's now Hobby for the Alfa and Geco for the S & W.
Walther CP-2 Match, FAS 604 & Tau 7 target pistols, Smith & Wesson 6" & 4" co2 pistol, Crosman 1377,
Baikal IZH 53 pistol, Gamo CFX Royal,177, Umarex SA-10 CO2 pistol.