It's very hard to judge from a photo, you have the upper hand in actually handling it, but from the picture it looks much more like pewter, can I ask why do you think it is silver?And why do you think it is old, there have been many people casting replica objects, which are very hard to date accurately. Also why do you think it is a kilt pin from the mid 1800's, yes of course it is a sword and shield design,but at that date kilt pins might have been an unusual item, so perahps a broach instead?
I'm not saying it isn't genuine, just expressing some thoughts