I have had this problem occaisonally as well.  One of the projects I am working on now has a female figure shooting a laser at some creature.  I tried using a premade laster freebie item from the web since it really doesn't require a lot of detail for the weapon, however when it parents to the V4.2 figure, it deforms and is ripped apart.  I have never been able to get it to work right.  I ended up designing my own piston in C6 Pro from scratch.