Metal Detecting

I found this in pasture about 5" down I think its a machine gun bullet but it appears to be hollow and something rattles inside have found browning cartridge cases in same area. I think its been fired as there are rifling marks. diameter is 12.9mm or 0.5"

im not big on bullets but it could be a tracer round as it is hollow, maybe .30 or .50 cal but not sure, someone will tell you exactly what it is, that i am sure of, GL

50cal tracer, used widely by the USAAF during WW2 and also on a lot of Allied tanks and other vehicles.

Hi,
wrong shape for pure tracer round but could have had a small amount of tracer inside. The rattling inside is probably a steel core as I suspect that this is an armour piercing bullet. To check see if it sticks to a magnet.

Thanks guys

tried it with a magnet - it has an iron core as hobster suggests