Artillery Fired Unexpectedly

[conchojack]

While demonstrating my Artillery, Serial # 3494, 1918 stamped on top of the barrel, the toggle hung open on a misfed round. I was using a clip from my P-08 Luger which has a much weaker spring than the one with the Artillery. The round appeared to be started corectly so I palmed the toggle down to close it. It loaded the round and unexpectedly fired. At the time I was holding the Luger grip in my left hand and slapped the toggle closed with the butt of my palm. We were very fortunate that the Pistol was pointing downrange and all observers were behind the shooter. The trigger was not touched and the applied force was directly down on the toggle. It should not have fired. The 9mm ammunition was Winchester solid copper clad. One other possibly unrelated fact. The toggle had not locked open upon emptying the clip. The clip was reloaded, inserted into the Luger, and the toggle was pulled back and released to load the next round. This is when the misfeed occurred.
Why do you think this Luger fired?
conchojack