I posted this on another thread recently.
The way I do it is to tape the end of the braid onto the spool Then I load all the braid onto the reel.
Now make your line to backing join and load the reel to about a millimeter shy of the lip of the spool (make sure the washers on the reel are set correctly for a perfect lay onto the spool)
Cut the backing when the spool is fully loaded.
I use a mandrel that I put into a cordless drill that holds an old empty spool, but you can also use an old reel with sufficient capacity... now tape the loose end on and wind all the line off the Stradic, backing first onto the spare spool/reel.
Then, using another spare spool/reel (I use an old buggered Penn 500 for this) wind everything off the previous spool.
Now you have the correct end with which to start spooling your Stradic and you know that every bit of your 300 yards will fit on. If you use sufficient tension in the loading, you should end up with the correct diameter on the Stradic (approx 2mm).
When loading less than a full spool of braid onto a reel, start with a few turns of mono first. Otherwise the braid may slip on the spool.
Also (don't ask me why I know this)... remember to take the silly little strip of plastic off the spool to begin with
