I can confirm that it works, 100% reproduction it seems.

Confirming, happened to us.

Tested it with a friend, both of us tried it, and it worked consistently, multiple times on multiple servers. The bug seems to be caused by the fact that you can reload the shotgun without a speedloader if you have a sawed-off in your backpack.

Steps for reproduction:

1. Put a sawed-off shotgun in your backpack
2. Reload the shotgun in your hand using R (without having a speedloader in your invetory)
3. Fire those rounds

At that point, the server will crash in a matter of seconds. This is a *critical* bug.