...what fool would place arrows down inside the barrel of a gun ?
The guy who's got one of these! The AIRROW Rimfire arrow shootin' drop-in barrel for the Ruger 10/22 or 77/22
www.swivelmachine.com/html/rimfire.htm
So, how far down the slippery slope are you willing to let things go? This is the next step beyond crossbows. Here's a quote from their website:
In the archery industry Swivel Machine Works is known as the manufacturer of the world’s fastest and most accurate archery products.
See? Just like the crossbow crowd, they call their product 'archery' too.