I have a Winchester 120 Ranger - which is a bare bones low end Winchester 1200 -
It was sold as a 4+1 capacity gun. So when I loaded the mag - I always put in 4 rounds.
One day I was wondering how much compression I was putting on the mag spring when it was "'fully" loaded - so I took a 5TH shell and pushed it in the mag tube trying to get an idea how much extra space there was in the tube.
The shell went all the way in with 1/8 of an inch to spare.
I still normally only kept 4 shells in the mag - but when I was at the range I would load it up with 5+1 and it functioned 100%.
I just bought a 10 pack of Wolff mag springs - they were ~~ $5 each or 10 for $25 - so I figured 10 would be a lifetime supply for me.
Since the Winchester is about 30 years old - and has been stored with 4 in the tube for at least 20 years - I decided to replace the original spring with a new one - It now only holds 4 rounds.