When lasergun shoots an enemy with shield, is it possible to do a crit against the shield multiplying the shield damage, or does the crit chance and crit multiplier only apply to the regular damage on the health of an enemy without shield?

Also, the descriptions state that the spikes, specifically, ignore shields, which would imply that the gunshot doesn't since it doesn't say they do, but are there any exceptions to that?

I mean, just, how does shield work in general? Does it block 100% of damage from turrets until the shield is destroyed, or does it only partially block damage?

To test, I just deleted all my laser guns so nothing (as far as I can tell) would be removing the shield. As expected, the spikes still did damage through it, but I also did see a gunshot be able to kill at least one Rockster that was not on the spikes. So it must be that some portion of damage still goes through the shield.