The SR-71 remains the fastest manned air-breathing craft ever flown.
But is it really as fast as a rifle bullet?
It is easy to get confused by aircraft indicated air speed, equivalent airspeed, true airspeed, mach number, and others. And speeds can be describe in units of feet per second or kilometers per hour, or furlongs per fortnight, if so desired.
Indicated airspeed is what your aircraft speed gauge indicates. After that, it gets pretty confusing as various pressure, temperature, and other errors get corrected to provide speeds used for flying the aircraft, navigating, or other purposes.
Mach number especially is associated with temperature of the air since Mach 1 is the speed of sound and the speed of sound varies with temperature.
Lets not get bogged down here in all that. But if you are curious, see skybrary.aero for detailed explanations.
See the white arrows in the illustration below.
This chart, comparing mach number with speed, tells us that the speed of the SR-71, around Mach 3.2, at the altitude it cruises at, above 50,000 feet, is about 1800 nautical miles per hour or knots.
Since 1 knot is roughly 1.69 feet per second, an SR-71 travels at about 3,000 feel per second.
This is roughly the speed of a bullet exiting the 338 Winchester Magnum.
As a side note, the blue arrows refer to in-flight refueling speeds. The SR-71 slows down to the slowest speed it can while the tanker aircraft speeds up to its highest speed. As the SR-71 fills with fuel, it must speed up a few knots. Fortunately, the tanker, as it loses fuel, can speed up a bit as well. It it cannot, the tanker will declare a “toboggan” and both aircraft will maintain their relative positions by slowly losing altitude.