The above being said, the SOPMOD is twice the price of the CTR and neither the CTR or the SOPMOD is normally offered as a kit with the buffer tube, spring, and buffer.
The SOPMOD was designed in Indiana by a Hoosier though!!! I met him at the last Indy 1500 and talked to him about his latest project, a 20mm vehicle mounted anti-material sniper Rifle.
Was it the folks at Crane?