Russia and China routinely checks their ICBMs using dummy warheads targeting atlantic and pacific coasts of the USA (usually a couple hundreed miles off-coast) to refine the old technology and to experiment with new. Usually the warhead is pirotechnically self destroyed as it reaches optimal for nuclear blast altitude. Small scattered pieces of magnesium alloy are not much visible on your radar screen after that.

So this is most likely the object you saw.

Also from time to time space debrie (old satellites) spiral back to Earth and usually small satellites burn on high altitude, but big chunks can make it to lower dense altitudes. There are about 5000 man-made objects orbiting Earth now.