A2 to A3 upper swap

[RavenVT100]

If I take my Bushmaster A2 config and swap in an A3 upper (so that I can mount a scope and use the removeable carry handle), will I also need to replace the front sight post? Are the posts a different size between the A2 and A3 variants when it comes to Bushmaster?

I'm building a new AR this year and I was going to go ahead and maybe use the parts from one of my ARs to help. It would involve doing this.

 

[DMK]

You shouldn't have to change the front sight post, but if you do, Bushmaster makes a taller one (just the sight post).

I went the other way with one of mine, changed a flattop to a fixed A2 handle. I think I had to rezero slightly, but definately didn't need a new post.

 

[RavenVT100]

I know it will need to be rezeroed. I just want to make sure it can be.