The exposed tabs are an in-elegant solution to a fundamental operation for co2 powered airguns.
I have used hex-drive 1/4 Whitworth grub-screws, but as the end is a small cup-point, a new larger cup needs to be added to locate with the end of the co2 bulb.
As I do not have a machine shop or welding equipment to hand, I need to be a bit 'creative' with my solutions...
The best bodge I have come up with so far is to wind the grub-screw into an M6 nut until the threads bind tight, I then file/saw/grind the nut down to give clearance, and finally, use a spherical grinding tool in my drill to create a cup in the top to seat the bulb.
A lick of black paint and the job's a good-un!
Obviously, the solution needs an Allen-key to hand, but for me, this is a minor compromise on my part to overcome what I feel is a major compromise by the manufacturers.
Too many guns, or not enough time?