Thanks for all the comments! I made some variations of laser cannons.
A. original fixed by 1 pin (will swivel around, as noted by dmarkng)
B. with drum holder used to hold it (the holes are slightly bigger than axle diameter, but I don't think it's a problem)
C. too thin for ma taste
D. those corners...
E. sleek, but the barrel is fixed by 2 studs only - it will not hold
F. part #17485 is not available in white (I made some color variations to differentiate the cannons a bit / simulate dirt), also the cross-axle doesn't go through the whole thing
I'm eager to hear what you think!
And also do you like the vest used on barrel tips? I think it's much better than previous solution.
Cheers!