A little history on the SOPMOD Stocks;
COLT ACR stock designed for the ACR program from the mid 80's
This was effectively the SOPMOD Stock with no battery compartment.
We have a few up in the museum.
In the early 90's Dave Armstrong at Crane liked the ACR stock, and certain SOCOM entities had 'pirated' them for their M4's, Dave wanted a method to put batteries for their PEQ's and SF lights in the stock so to have mid mission replacement ability on the gun.
Crane started making these stocks in the late 90's
In the ealy 2000's Crane offered the TDP up for bidders, ARMS and LMT where folks who submitted bids to produce them.
LMT won and had the SOPMOD stocks produced to for them and USSOCOM.
Recently LMT lost that contract to a new company in 2010 and BB5 Systems from Ohio is now making them and selling them to the Army for $25.00
In my opinion, the SOMOD was a great stock - however its been far eclipsed by the CTR and ACS stock from MAGPUL, and thats evolution for you.
Dave Armstrong let his patent expire in 2009 (IIRC) so manufacturers like Magpul and VLTOR etc no longer have to make modules for the battery compartments but can mold them right into the stock.