He's 5 - so ones similar to this is easier to "prime", given the handles attached to the spring mechanism.
I don't think it's the darts - as they work beautifully with other blasters (we've got an RD-6 which works painfully well).
I'll see how it goes if I keep the cylinder in place (need to find some darts - as they're not with me at the moment).
OK - so when I hold the cylinder in place, the dart comes out quite slowly - maybe 2m air, and then lands. Super weak actually :(