First stripped the barrel down for a thorough cleaning.

The Beast:
Please note, not a real M-203, that would be illegal!
This is a M-203 replica smooth bore flare launcher.

The first session I ended up with this:

A little more work:

Some precision cutting with a less then precision Jet bandsaw

A rough fitting:

A little fine tuning, cut the groove for the gas port:

The quick release pin block:

Mean looking front end:

Got it back together this morning: