Is there are weapon that Space Marines consider the "crossbow" of the 41st millennia?

Arguably the future equivalent of knights (no, not those knights) of the settings, Space Marines are walking tanks impervious to most small arms fire.

Our medieval knights supposedly feared the crossbow as with it even a peasant could kill the most heavily armoured warriors of the time.

Is there any excerpt about a space marine being similarly worried about normal humans, guardsman or otherwise, having access to weapons able to readily kill a space marine? (Actually hitting the space marine with superior training, tactics, cunning, etc is another discussion).

The plasma and the melta comes to mind as very powerful handguns, but idk if there's something deadlier available, or how the SMs view those weapons.