5.56 Nato ID


I have the below 5.56 Nato cartridge and haven’t seen one like this before.

I am wondering if this is a plain ball round or if it might be a proof? If it is a plain ball load, why the nickel case?

Any information is appreciated.



Heavyiron–It is most likely a proof, as you suggested. A nickeled case was the standard military ID for HPT cartridges in 1965. This one was made by Remington Arms.

It is a proof load.

The correct designation for your round is “M197 High Pressure Test (HPT)”. It is identified by its plain tip and silver, as opposed to brass, case.

Here is a link to a nice web page that describes the history and the various standardized rounds for the 5.56 x45, 5.56 NATO and .223, all of which are technically different cartridges.


Thank you guys for the information.

Ron, that was a good website.