If the piston still sticks thru above the backing plate remove a little more from the tube. Now unscrew the end cap and install the new buffer spring. Place a drop of blue or green loctite on the threads and reinstall the end cap. Reinstall the outer assembly and the snap ring.

Thats it and the stock ready to for use.

Should this be something you may not want to do, Send me your A3 stock and a check for $65 and I'll supply and install the kit and return it to you.