fn509

I was searching for a nice red dot for my 509T and got so giddy looking at best optics that I ordered a Holosun HS510C without checking to see if it would fit. While I'm sure I can find a place to put it if it doesn't fit the 509T, I'd still like to know whether I need to get something different...

so... I have been shopping around a little trying to decide on who I want to use to cut my slide for a sight on my 509 and that's not backlogged for 10+ weeks. I have two questions 1) a couple of the shops are saying that the Trijicon RMR "WILL" co-witness with the factory sights and others are...