There are lots of good videos (and some not so good) on You Tube that show how to do this. You can also use the
New England ropes Splicing Guide to show you how. I splice Sta Set all the time.
A couple of hints. When you get to the part where you have the core out of the cover and you slide the cover up and then pull it back down (step 2 of the double braid splice), Don't try to get every last bit of slack out of it. That will make it harder to bury the core at the last step.
Second, when you get to step 4 where you insert the core into the body of the line... I have found that if you use a fid the same size of the line and work that into the line WITH OUT THE CORE ATTACHED it will "open up" the line a bit. Now, attach the core to the next size smaller fid and it will go through a LOT easier.
Oh, and DON'T use regular masking tape; it has too much friction. I tape my cores/covers w/ Scotch green FINELINE tape and it slides through a lot easier.
When you bury the splice (step 9) put on some heavy leather gloves to work the cover down over the splice. Make certain the knotted end is SECURELY fastened! You may find that the eye has some cover all bunched up even after the core is buried. Take a good stiff metal rod (I used some 3/8 steel, or a big screwdriver), insert it in the eye, hold both ends and SNAP the line with a HARD jerk. A couple of those will seat the cover and core and you end up w/ a nice looking splice. I find 3/8 to 1/2 inch splice easiest. 5/16 is doable, 1/4 just p!$$ed me off!
Have fun.