My .50 makes the same kind of noise...
Simply not true.
The NASA Free Flight Ballistic Range in Sunnyvale, CA has achieved Mach 18 or something close, and by firing a projectile into the muzzle blast of a cannon (firing blanks) at the far end of the test chamber, Mach numbers in the low 20s can be achieved.
Mach 10 is not to be sneezed at, but it is far from the biggest in the country.