I have been running my QB79 .177 off a "refillable" 88g cartridge. I bought a 12g adapter off the bay for a few bucks, tried it out today:
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I got 24 good shots (on target at 40ft); I shot one 12 shot group that was 1/4" high and about 3/8" o/o; the next 12 shot group was right on the dot, about the same size, then the last 3 went low. I waited 20s between shots.
Pretty good for 1 cartridge.