I should have went with the old measuring tape and got 4 1/8 lol it was fun, it is 1/8 longer. To be honest that 7th round was tight. Will take the longer and 7 plus 1. I am not going to complain. It would have been very tight even lacking that 1/8 so I am happy with it.
You'd be amazed at how far mag tubes extend past the muzzle in competition/race guns. Crazy. Depends on what type of shells you're shooting, of course, but here's a good extreme example: