what are some methods of applying texture to wood stocks before painting?

Texture

is there anything more "bumpy" and less "rough"

You can make it more or less bumpy depending on how much you work with it.  Also once dry you can knock it down with some 220 grit paper and it will look exactly like the texture on a McMillan stock.  It's not an exact science and it can be tailored to however you like it.

There are other products that guys are using but again it's not an exact science.  You have to experiment with it to get the look your after.  There is no product out there that you can say will give you a particular finish every time.  Kind of like a Krylon paint job, no two are alike.