I modified the chamber to take the new closed top mag instead of an opened top mag. Its mostly for preference
Step 1: Magazine
Just do that. And you'll probably want to wrap it in tape so it doesn't open up randomly.
Step 2: Remove
Remove the top three parts from the gun and it should look like how it is below the parts
Step 3: Modify
Modify the old parts (top) with the new parts (below)
Step 4: Replace
Replace the new parts with the old ones
Step 5: Congrats!
Congratulations! You have now modified your Hymn of the Dead to take top closed magazines now. Regular magazines will no longer work and the top closed mags are a little hard to get out.