Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4495637.

Another pass, this time with different muzzle types that you can swap.

This is a 4 shot inline mag for the Nerf Mega Bigshock. It allows you to put 3 short (3.5mm) darts in the mag and one in the barrel. To reload, tip the barrel down while priming and then fire away.

Materials: This print One 40mm length of 17/32 brass tube Some tape or glue

First, you will need to take out the AR and dart post by whatever method you want but you will need a clear path to the back of the blaster. I used a flat head screwdriver to pry the cap on the back of the barrel off. If you are careful it can be glued back on or print and eventually, after test fitting all the parts, glue in one of these

https://www.thingiverse.com/thing:2235606

https://www.thingiverse.com/thing:1277598

Once you have a clear path to the back of the blaster you can test fit the print and use some tape to get an airtight seal and allow the print to seat all the way back. Also, make sure the sight is on top, and the channel lines up with the plunger tubes air hole.

The next step is to cut 40mm of 17/32 brass tube. Make sure all the rough edges are sanded smooth and a dart can slide in without catching. Test fit the brass in the end of the print, it should seat on a lip inside. If it's not airtight try a layer of tape or you may want to glue it in.

In the end, you may want to glue the print into the blaster to make it perfectly airtight but I'm getting acceptable performance without gluing the print in the blaster or gluing the brass in the print.