Hey, I was going to rack peoples minds on this site and see if anyone knows of different butt stock producers for the pistol.  The Buffer Spring tube (also being made of the carbon) is unique in that a center pin runs the length of the tube and a much smaller buffer spring is utilized.  The 97S rifle stock is not compatable for the pistol for obvious reasons, but I am trying to find out if the collapsable stock sold on regular C15 rifles is. I am all set on gunsmithing and I expect to encounter some issues which-ever route I go.  The 97S I am building is tax exempt and NFA registered SBR because it is for my employement so no one needs to worry about that.  Thank You for the help.  

-TrCp

Do't everyone answer at once haha.  I got up wtih a connection at Bushmaster, and in case anyone else in interested: Bushmater C15-97S's cannot initially accept a butt stock, but you can ship them to beautiful Lake Havasu, Arizona to the Carbon plant and get them custom machined.  They need to do some customization to the lower.  Mine will be in route.  When I finish I will post a pict or two if the management is all set with it.

-TrCp

How is building it for your employment "tax exempt"? Could you explain?

If you check out an ATF form 1, there are 3 boxes in the Type of Application section.  Two of them are Tax Exempt and my weapons fall under box C. I have an interesting job.  

-TrCp

The carbon buffer tube uses standard size threads.  You can put a carbine stock on the pistol, you will have to use a normal carrier, carbine buffer and spring. The reciever does not have a recess for the retainer plate. However you can reverse the plate and drill a hole in it to line up with the threaded hole in the reciever and use a screw to secure it.