Well, there are SAAMI specs for max COL for 7mm Rem Mag. I think its 3.29". But it doesn't really matter. What matters is pressure signs, and does it fit in your magazine and will it chamber without shoving yourbullet into the rifling. Reason for the max SAAMI specs (IMO) is to make sure your not shoving the bullet into the rifling. Most companies these days cut the throat so long, it doesn't matter. They do it for pressure reasons IMO.

There are a few tricks to find out what is the max you can load a bullet in your gun. Bunch of tools out there to measure it like stoney point's and I think hornady bought them. I like em, not totally necassary. But another cool toy.

But you can take a sized case, take a dremel tool and split the neck and little into the shoulders on one side. This way you can insert a bullet and it will hold but will also move. Chamber it in your rifle, and carefully, ( I mean carefully) remove the brass/bullet combo. And measure the total length. Do this for a few bullets and a few times. This will tell you how far you can load too. But then you need to make sure it fits in the mag.

If you get a lot of variation, don't be alarmed. The ends of bullets vary due to being lead. Proper way to measure a bullet like this is at the ogive. This is where the bullet makes contact with the lands and groove. And again, lots of tools out there to measure at the ogive. But right now just keep it simple.