I appologize for asking cause I know that this has been asked before but I want to be sure I'm doing it right and don't screw up.  So I'd appreciate your indulgence and help.  I have an RRA Entry Tactical with the fixed car stock and have just received a RRA 6 position collapsible that I would like to install.  Can someone give me step by step instructions (without skipping even the smallest deatils) for removing the old stock and replacing it with the collapsible?  I tried removing the castle nut with my car wrench but it wouldn't budge.  Before I really mess up I thought I'd better ask the experts.  
Thanks

1.  Remove buffer and spring from buffer tube.  Remove castle nut with CAR wrench.  Sometimes they are a little snug, get a hammer and tap the wrench.  Might help to put your lower loosely in a vice, protected with a towel or whatever.

2.  Back castle nut all the way off, then pull back car stock retainer plate.  There is a spring there that goes into the lower that holds pressure on the detent for the rear takedown pin.  Just be careful and leave it in there... or take it out (spring) for now.

3.  Remove buffer tube from lower by unscrewing.  Sometimes they are tight.... so the same applies as #1..... apply force.... it will bust loose.  Once it breaks loose, go SLOWLY and hold the buffer retention ping/spring or it will launch across 3 counties.  Unscrew all the way out.

4.  Screw in new stock buffer tube.  Push down on buffer retention pin/spring and screw tube over the top of it.  Dont go too far... the tube should just barely cover the pin enough to hold the pin.  If you go one revoltion too far, the upper wont close on the lower.

5.  Push stock retainer plate against takedown spring and lower receiver, and hand tighten the castle nut.  Then using CAR wrench, tighten up the castle nut, making sure stock is straight up and down.  Some like to use a little blue loctite on this nut.... to each their own.

6.  Insert new CAR buffer and spring.... assemble upper, and function test.

I used the above instruction, and all went flawlessly. For Colt 6400C models, use a punch/nail/dremel on the 2 stakes on the retainer plate that hold the nut from turning. My buffer retaining pin didnt even "jump" out of the hole it sits in. Make sure you align the pin that holds the lower in place properly, or youll end up pulling out the pin and taking everything apart again. I figured it out before everything was back together. Also make sure you put the retaining plate on the right way, bump inwards :) Youll have a hell of time getting everything together until you do.

All in all, without any problems, a 10-15 min job if you take your time.

Took me an hour 'cause I got excited, hurried, and didnt bother to read instructions.

Alex