I guess that depends on what you are using. If it is a Precarve with a Lock Inlet, you do the lock 85% of the way first, then put the barrel in to the correct position, then after that is successfully accomplished, you do the tang.
In this instance, if you do the barrel first, your vent may not be in the proper position, as you can move the barrel, but the lock is going in where they inlet it.
Comprende ?
If the stock has NO Lock Inlet, you do the barrel first, tang second, then the lock.