Board Thread:General Nerf discussion/@comment-27035444-20160728160238/@comment-3362895-20160728163737

The only aftermarket metal cylinder I can think of is the six-shot one offered by OMW. That's straying even further off your desired path.

Perhaps the other way around the five-shot limit is to make your own quick-detach, speedloading cylinder system, and use the cylinders scavenged from three cheap Hammershots to rapid-reload.