Pair of Queen’s Westminster Rifles buttons (later the Queen’s Westminster & Civil Service Rifles), which became part of the King’s Royal Rifle Corps family.

Both are large white 23mm metal (silvered) buttons with a brass back, made by Samuel Brothers Ltd, London - a well-known military outfitter and button maker based on Ludgate Hill. The fact that both share the same maker but have different crowns is the key detail here.
The design
The face shows the Royal Arms on a shield, with a chain border around the edge -  Queen’s Westminster Rifles (later the Queen’s Westminster & Civil Service Rifles), which became part of the King’s Royal Rifle Corps family.
∙ Left button - Tudor/Imperial crown = Victorian, pre-1902
∙ Right button - St Edward’s Crown = Edwardian or later, post-1902
So you have one Victorian and one Edwardian example of the same regimental button, from the same maker, which is a lovely matched pair from a collecting standpoint.
The regiment was formally the Queen’s Westminster Rifles, raised in 1860, so the Victorian button could date anywhere from the 1860s to 1901.