Apparently being a world reknown competition shooter sponsored by one of the largest gun companies in the country has perks that being a lowly gun blogger does not. One of those perks seems to be the ability to shoot ultra rare guns.
In this video, Jerry Miculek gets to run a 1957 AR-10 prototype through its paces. This little guy has the fun switch and everything. We do get to see some high speed camera action, but it looks like the lighting is a little off on those shots (still watchable though).
Here is a little history on the AR-10 platform (via Wikipedia) [emphasis mine],
The AR-10 is a 7.62 mm battle rifle developed by Eugene Stoner in the late 1950s at ArmaLite, then a division of the Fairchild Aircraft Corporation. When first introduced in 1956, the AR-10 used an innovative straight-line barrel/stock design with phenolic composite and forged alloy parts resulting in a small arm significantly easier to control in automatic fire and over 1 lb (0.45 kg) lighter than other infantry rifles of the day.
Over its production life, the original AR-10 was built in relatively small numbers, with fewer than 9,900 rifles assembled.
In 1957, the basic AR-10 design was rescaled and substantially modified by ArmaLite to accommodate the .223 Remington cartridge, and given the designation AR-15. ArmaLite licensed the AR-10 and AR-15 designs to Colt Firearms. The AR-15 eventually became the M16 rifle.
As you can tell by those production numbers, this is an ultra rare gun to still be around in firing condition today.
Some people get to have all of the fun!