Dave,
I haven't tried it much with injection-molded stocks, because so many made these days are too floppy no matter what the length of the forend. However, those that are stiffer (and some companies are doing that with cross-hatched bracing inside the forend) generally work well, though if they DO bend too much, can usually be cured with a round rasp used on the 2-3" behind the tip of the forend.
Some are just hopelessly floppy.
