It all depends on what kind of receiver extension you have. I believe the Doublestar rifles use commercial spec tubes. Here is an illustration explaining the differences:
If you want a really good cheek weld, get a Magpul ACS!
Thanks hottnucks! I just found some info on the DS tubes and they are commercial spec. I don't think the ACS will do for me what I need. If the CTR measures the way it looks in the pics I should be able to hold the rifle slightly higher on my shoulder than with the original m4 stock. The rear plate on my stock measures 5 1/8". The CTR-C looks like it has about 1/2" more real estate.