Here is the stock BBB.
The first thing to do is to obviously open it up. The internals should look like this: (you only need to open the front half.)
Make sure you do not lose these pieces as they keep the blaster primed. (There is one on the opposite side of the blaster as well.)
Pull off the main barrel like this, it easily seperates.
These pieces should just fall out.
The long post is connected to the main base piece with a glued spring, so pull it of and cut back the AR like so.
Then put it back into the barrel without the long rod piece.
Set the barrel and AR piece aside and focus on the plunger head, which should look something like this.
If you twist the plunger head while holding the plunger body, it should give way and came off, which will leave you with this circular piece still attached. If you push this piece the away from the crack in it it should come off, allowing the spring to just fall out. As you can see, I have added a NF spring, aswell as the stock spring.
Now go back to the front barrel, and there should be four nubs in the top of the barrel where the AR post was, if you have a dremel you can dremel them off but if you don't, (like me) you can shove a pair of scissors down the barrel and twist , they should seperate.
These important pieces that you saved go into these slots here.
File down a length 16mm conduit until it fits snugly down the stock barrel. Put it all back together and it should look something like this.
Your done! You know have a fairly accurate gun with decent ranges, so load a fresh streamline and blast away.