[Will Keir] “is there any articles or form posts have detail this method for FCP”
Search the forum. There are tons. You should maybe do a search over at After Effects and Motion, too.
[Will Keir] “Do you mean to just take a movie with Muzzle Flare effects, somehow isolate just the Flare part of the screen”
Eh, no not really. That would actually be illegal (if you took it off “some” movie”
You got a good description on how to make one of the effects in one of the other posts, and a place to buy stock photo.
As to compositing, that’s a good idea. Have a read in the manual.
Gunleik