What are these?

[LCplCombat]

White metal, looks like chrome. SB in the Diamond shapes on the headstamp. Around the shoulder it says "UTM 5.56 RH" and just above the rim it says "14"

They must be 2 piece because they open a little way but do not come apart.

 

[doppz92]

If I am not mistaken these a .223 spent training rounds.

All relevant info here: http://utmworldwide.com/

 

[kahu1]

UTM rounds ,these look like they must be UTM Blanks.
Usually have a small caged plastic 'lipstick' projectile for man marking.
Doesn't look like these had a projectile that fires.

 

[smle2009]

Yes they are UTM 5.56mm silent blanks,when fired the rear section is sent rearward to re cock the action,much like the 9mm SMAW spotting round,there is a small ball bearing inside that is propelled forward to strike a small primer which makes a very quiet 'bang'.
Photo is of a sectioned one of these that was very kindly done for me by spotter a few years ago.
As Kahu 1 says there is also a 'marker' version of these which fires a small plastic 'bullet' that contains a marking gel...these are also found in various 'loads' in 9x19mm

Atb
Tony