Seeking recommendations for pellets that don't fall out of Umarex clip

I use a .177 CO2 powered Umarex pistol that uses the standard circular Umarex 8-round clip/magazine. Currently we load it with RWS 7.0 grain wadcutters. We use the gun to dispatch cane toads in SW Florida. Spare clips are kept in a fanny pack. But during the course of an evening's walk around our golf course, several pellets slip out of the clips in the fanny pack.

Any suggestions on wadcutters that will provide a tighter fit (head or skirt) in the clips? Are there sources of information on skirt and head sizes of wadcutter pellets? Hard Air Magazine seems to have fairly limited information. Published information and data on airgunpelletdb.com don't seem to have actual head sizes, just the nominal publicized sizes. I'm hoping to find what real world experience shooters have had, e.g., which pellets give a tight fit in clips.