Indian Volunteer Rifles buttons

[natal01]

I am a sometime collector of buttons. I collect them if I think that they are unusual or attractive. My "collection" has no real theme but one day I might get some sort of order into the assemblage. Today I acquired these Indian Volunteer Rifles buttons. The buttons in the first picture are easy to identify as they have the good grace to spell out their names. The two buttons in the second picture are not so obvious. The brass button from Bhopal has a central shield superimposed on crossed rifles. The initial SBI (or some variation thereof) are in the shield. Any ideas as to which unit this might be ?
The small white metal button has a victorian crown over the initial AVR in a wreath. I guess the VR stands for Volunteer Rifles, but what or where does the A represent.
Any assistance would be much appreciated .
Thanks
Mike