If you have a bit more $$ you might consider a chassis rather than adding bottom metal to your existing stock. They come with the removable mag option built in and provide a very stable platform for your action.

What you are paying for the bottom metal kit only from CDI will get you half way to the cost for the MDT chassis without a buttstock. You can use any old AR-15 buttstock assembly on it or something fancy. Weight is under 2 lbs.

http://mdttac.com/lss-chassis-system.html