I've resized many a shell with my Mec SSer be it 10, 12, or 410. Cheddite made, or still makes two different size primers. A larger one for Europe and the standard 209 for the USA. I haven't seen the larger one for quite some time now. Probably 10 years ago I was loading for the wife, daughter, grand daughter, and me between 30 to 40 boxes a week and at that time was using Cheddite primers. That's somewhere between 35 to 40,000 shells a year and never found a oversized Cheddite primer. I could go back and forth between Cheddite and Win primers with no problem. They all went in just fine using a Mec 650. The only problem was 28ga Remington hulls. The plastic base has a smaller flash hole that a #1 drill will open up so primers other than Remingtons will go in. We have maybe 50 shotgunners at the club, many of them using Cheddite primers. I have never heard of anyone having problems with the Cheddites making the shells expand. My wife has a Beretta O/U with tight chambers. I had to use the super sizer for any shell fired in a different gun.You must have some other problem than Cheddite primers expanding the shell. Yes the RIO and Fiocchi primers are a bit larger. Once used you have to keep on using them. But I have never heard of them expanding the shells outside diameter. Just the primer pocket making them too big for other primers to stay in.