I use a hack saw or dremel wheel to make 4 cuts down the case neck to just above the shoulder junction. I file the cuts smooth inside and out then lube and size it just to make sure it doesn't bind up. You should be able to slide a bullet into the neck so it rests in there. Next, I cover the bullet with sharpie, rest it in the case and chamber it. If the bolt won't close (shouldn't take more force than normal for chambering a round), I take the case out and cut a little deeper in the neck toward the shoulder, file and size and try again.
If you get a bullet stuck in the lands, a couple sharp raps of the butt on the floor should jar it loose.
Once the case is where it needs to be, I mark up the bullet with sharpie, chamber and carefully extract. If it works right, you should be able to see rifling marks on the ogive of the bullet. There will also be marks on the flat of the bullet from the case. If you can see these when the case is extracted, the bullet has shifted during extraction and the process needs to be repeated.
I do 5 or 6 measurements just to verify that I've done it right.
Good luck!