I usually whisk my egg whites/sugar in with my bowl mixer over a small pan.  I used my new double boiler and mixed until it reached 160 degrees.  I added it to my mixing bowl and started mixing at a high speed as I always do.  I noticed when i had soft peaks that it looked a little grainy, but not to bad, so I kept on mixing.  I added the butter and it took a while, but it came together and it was fluffy.  I just tasted it and it's gritty.  It taste good, but the sugar it noticeable.  What do I do know?  Do I put some of the batch in the microwave to melt and then mix together?  There doesn't seem to be any consensus anywhere on what to do?  Thanks!

Ado you have a fine strainer?

Yeah

AThat should work but test it because you don't want to just force them through into smaller pieces -- plus watch out for it getting too warm and soupy -- use small portions -- hope that works out for you

http://www.cakecentral.com/t/594605/making-smbc

https://fromscratchsf.wordpress.com/2011/03/08/tutorial-swiss-meringue-buttercream/

http://www.woodlandbakeryblog.com/drum-roll-buttercream-is-here-tada/

just to add.....that when you watch the woodland bakery video you will see her stir the sugar into the egg whites with her hands while heating them  It does not need to get very hot to get the granulated sugar to dissolve.  I use a really long wire whip to stir mine, and after a few minutes I can feel the mixture with my fingers and tell that the sugar has been dissolved.  You can always feel the grains of sugar as they feel gritty.  and make sure that you scrape the sides of the bowl to get those sugar granules dissolved.