www.makemkv.com

I have been ripping the complete Blu Ray and as noted by others IT TAKES UP A LOT OF ROOM! So I decided to try the MKV route. My problem is when ripping a movie how do you know which is the main movie? Example This Means War has 2 main movies, I ripped both to see the difference one comes up a full 7 minutes and 1 gb larger than the other. I checked the time line on the disc and it matches the smaller main movie. Looking further into the original disc I see nothing for additional options ie alternate endings, added scenes etc. Whithout watching both movies why would there be a 7 minute addition to one of the files?

"What is the main movie" changes with each disk. If you look at a Lionsgate disk, for example, there are dozens of possibilities, one of which (varies with the disk) is correct, while Disney-related disks have just two or three (correct one varies by the language selected).

Using blu-ray.com, there is a 62.5% chance there's an "Extended Cut" on the disc. I'm guessing you're mistaken about something. However for the filesize, an "Extended Cut" may have different audio streams than the "Theatrical Cut". For example, "The Chronicles of Riddick" has a higher quality audio stream for the "Theatrical" than it does for the "Extended Cut", so this can cause a noticeable difference in filesize. Also semi-related, you also have to make sure what "Cast/Director Commentary" streams are for, "Extended" or "Theatrical".

This Means War Blu-ray
Extended Cut + Theatrical / Blu-ray + DVD + Digital

https://www.blu-ray.com/movies/This-Means-War-Blu-ray/39328/

It seems just about every release of this title has both an extended cut & theatrical cut. It probably says so right on the case.