I want the Magpul CTR stock but it does not come with all the buffer tube items. http://www.mountsplus.com/miva/merchant.mvc?page=MSP/PROD/Magpul_Stock/MAG-310-BLK I have a DPMS 16in AR-15 with the fixed stock. Now can I use the buffer tube from the fixed stock for the Magpul? If not what type of buffer tube do I need I what website sells them. I'm an idiot with this buffer tube thing. I'm new to AR's.