... Never had a semi auto brand new shotgun so would like to learn and know what would be best ???
You might get more thread traffic in one of the shotguns subforums. It's a fair question but be prepared for a wide variety of replies.
Some people think break-in is important, and others don't. If there are recommendations in your manual, try them. Or don't. As long as you're using shells that are the same as what is stamped on the barrel you're not going to break it, whatever ammo you use. However, if you're concerned about potential warranty issues then make sure you follow the manual religiously (if it has anything to say about break in).
One of the reasons you sometimes see manufacturers recommend heavy loads during break in is that new semi auto shotguns tend to function better with heavy loads. They don't want customers to send in a warranty claim because theirs malfunctioned with light loads right out of the box, when the problem would be cheapy solved (for them) with X number of heavy loads.
Personally, I prefer to use light target loads for the first 25 rounds and then assess. It gives me a chance to see if the shotgun will tolerate light loads right out of the box (as some do) which saves me money. If it does malfunction in that period, then I get to see exactly how it malfunctions in that situation - This is helpful for diagnosing future malfunctions, if they happen. If it's happening a lot in those first 25rds and I get bored of clearing malfunctions, then I switch to heavy loads for a while. Switch back to light loads whenever you want and reassess.
One additional recommendation you'll commonly see is to do a complete disassembly, clean and lube before break in. Sometimes new guns leave the factory with manufacturing or packaging debris in the action, which can cause problems. It's also a good way to get to know your shotgun. Oh, and hand-cycling the action (with or without dummy rounds) also helps to break in those moving parts, albeit much more slowly. And it's not very fun.
