What is the best way to a the stud on my Hogue forend? Dirll and tap or drill and use a washer and nut on the inside ? will use it for a sling and bi-pod.

I think both are perfectly acceptable with the drill and tap slightly ahead in professional appearance if the sling stud protrudes the proper depth. If it's too long use the other method.

It's all in the minor details such as if using a the nut and washer method I think a hard plastic washer or aluminum washer so it can slightly dish some to match the inside of the tube inconjunction with a steel and nylon lock nut would be the best way of doing it.

-M

You will likely not have enough thickness to tap out a decent thread. A thin washer and a nut behind it inside the guard will work well.