I was out shooting my AR yesterday everything was going fine, then I reloaded and I couldnt pull the charging handle back, I opened the gun up and my buffer retainer was out, and the retainer spring was caught up in my charging handle, Now I cant get the buffer retainer to stay in and my takedown pin keeps falling out... I dont know if the 2 are related.. do I just need to replace the buffer retainer?

The buffer retainer can not fall out if installed properly. The larger shoulder of the buffer retaining pin must be captured down into it's little hole by the buffer tube. On the rifle tube when screwed into the receiver untill the shoulder bottoms out this will be the correct position to capture the buffer retaining pin shoulder.

With the collapsing stock you must screw the buffer tube in untill it traps the pin then spin up the locknut on the stock and tighten.

The buttstock retains the spring and detent throught the back of the receiver and applies pressure of the detent onto the rear takedown pin when the stock is tightened in place. Either the stock is loose or you have lost small spring or detent parts.

oh, ok, thanks alot

Not nessacerly, it may be possible that your lower receiver is built out of spec- like mine.  On mine I had the same problems for years until I took it to a gunsmith and he informed me of my problem.  Instead of getting it remanufactured by Eagle Arms, I got him to custom make me a standard buffer tube by milling away at part of the buffer tube that screws aginst the receiver.  I used that for a while then I wanted to have it back in the origional CAR configeration but my CAR buffer tube would not fit properly unless I had it at a 90 degree angle from where it was supposed to be.  To remedy this, I filed away at the threads on the buffertube until it fit properly.  So if you have a 1991 production Eagle Arms in the 635X serial number range this might be your problem.

it is actually a fairly new bushmaster M4-A3, the stock wasnt screwed in far enough to hold in the retainer, like TommyBrown said, so I fixed that, but the takedown pin still falls out. maybe I need a stiffer spring under the buffer retainer???????

Your takedown pin is falling out because you're missing the takedown pin detent and/or the detent spring.

They probably fell out when you removed the buttstock and you didn't notice it.

Well thats what it was, (duh..) This is my first AR so I am not completly familiar with them yet, yep the takedown detent and detent spring are gone. Bushmaster has them for $ 0.50 a piece, but they want to charge $8.50 for shipping, I know thats only $9.50 but I cant pay $8.50 shipping on $1.00, just feels like a rip off, no one in my town sells AR parts, any one know where else to get them for actual shipping charges????

Are you sure the detent fell out?  If it's still there you can use another spring like the one from a bic lighter.  Also, for some reason my spring was in 2 pieces, so I used a pice ofthe straw from a WD40 can to add the length I needed to push the detent in.  If the detent is missing you can try using the straw and the bic lighter spring.