Re: Back of bolt not cut straight...
That appears to be the cocking piece you're referring to. If the rear surface is not straight, it shouldn't have any adverse effects. It is connected to the firing pin, through the shroud. If the shroud is not machined true, it will put lateral forces on the firing pin, and with enough use, can create wear on the firing pin hole, causing it to oval, and the firing pin will not strike the primer correctly.
Remove the bolt, release the firing pin and watch how it prtrudes through teh bolt hole. make sure it's extending through the center, and not rubbing on the sides. Remove the firing pin and check the slot on the shroud to make sure it is true. Also check the firing pin to make sure it is straight. If necessary, replace the bolt shroud and see