I would like to replace my fore end and buttstock on my Sith and Wesson MP15 (plain AR). How do I know what stocks to get?  I believe that the buttstock is either mil or not and you measure the diameter of the buffer tube? And what length/type of fore end? I would like to have the option of adding a bipod and maybe a verticle grip. Another question I hate the pistol grip, which seams small waht do you recommend to get to get my trigger finger in a better position?

Thanks

Stocks:  Measure the diameter of the extension.  Mil spec is 1.14, commercial is 1.17

Hand guards:  Carbine is about 7" between the receiver and the front sight post.  Mid is about 9".  Rifle is about 12".

MIAD grips are adjustable for size.

You can put a bipod on just about any hand guard, but of course rails or the ability to add rails is easier.

m&p's have mil spec buffer tubes. and you have a 7" (carbine length handguard) .

A Pearce 1911 pistol grip and a G27 pistol grip are more of a hand full for a bigger grip. If you like the feel of an A1 grip an old Lone Star Ordnance pistol grip is a little bigger.

I favor the CAA UPG16 grips.  I have big hands and use both large straps.  Plus the rubber straps feel much better and offer a good grip surface.  Found they help on heavier ARs