Old 1970's 2 3/4" 1100. It had a tiny crack in the receiver behind the loading handle slot. I drilled it and the crack stopped. The receiver has nothing to do with locking strength anyway. I have been shooting it with low brass target loads and it functions great.

I modified the barrel to use choke tubes with an adapter sleeve.

I wanted to try it on waterfowl. I currently use HW-13 2 3/4" loads I had loaded in quantity a few years back. They are not "hot". Just high quality reloads using an exact book recipe and all new components. The power is "steel".

Should I be afraid of using them in the old 1100?

Easiest way to know is to call Remington

personally, I'd scrap the receiver...1100's are too cheap to take a chance on... they can be had for under $300...and the tightest choke I'd use steel on would be an improved modified...

I don't think the receiver is going to pose any problem. It's my understanding that the barrels of today are made from much tougher and harder material than the barrels of yesterday. The fact that the new shot is harder than the barrel steel is the reason why we are seeing so many old barrels with bad score marks running the length of the bore. Choke tubes will make it pattern better with hard shot, but it won't stop the bore scoring. But in an old 1100? I don't know that anyone is going to poopoo or put a hex on you for destroying it. As above noted, they are a dime a dozen now days and I don't see them becoming anymore collectable than the old H&R Topper shotguns are today.