The drums you need for this HPA ADAPTER are sold separately, they are available here

These drum magazine adaptors are the most sensible looking option you’ll find on the market! The smaller MP5 style drum matches the calibre of the pistol making it extremely compact.

Assembly:

Looking to install the adapter yourself? It’s easy! You’ll need a grip vice, 2mm punch pin, screwdriver set & a hammer/mallet.

1). Remove the upper shell from the drum magazine by undoing the screws on the sides of the MP5 mag section & pull apart.

2). Punch out the pins from the drum magazine to remove the MP5 section entirely.

3). Punch out the bottom pins on the sides of the gas magazine to remove the gas block.

4). Punch out the small pin that retains the follower at the bottom of the gas magazine

5). Insert the single stack adapter into the gas magazine.

6). Fit the gasket to the Airtac HPA adapter (at this stage you can apply some silicone oil to the gasket to aid insertion )

7). Place the HPA Adapter into the magazine, and into the clamp. Tighten the clamp until the pin holes line up, and gently hamer them.

8). Push the drum into the bottom of the HPA adapter, and insert the drum pins through the sides of the adapter into the drum

9). Go have fun!