Well, took the Maxi to Contenders this past weekend (East Coast Ruger Gathering) with the 194 gr Bradshaw/Martin loads and the MBC 180 gr loads and had a ball. Even with the relatively stout 18-18.5 gr loads it was FUN to shoot and recoil really wasn't that bad. Had a couple that wouldn't load (that was probably my fault, and they were done early in the loading process) and had a couple with primers that didn't go off (in this case they were primers that were fairly old so I just don't know - I'll pull the bullets/powder and deprime). All shot to POA and really moved the swinging steel plates. Then shot a few 180 gr / 13 gr 4227 that Kevin from TX brought. Nice mild load that again shot to POA. Soooo, I'll now load some different loads with various IMR4227 powder weights to see how it does. I probably will not be using it for hunting at this time so I'll lighten up on the powder to just have fun and leave the 18+ grains loads to hunt with if I decide to go that route.
This is just a plain old fun gun to shoot and I had/have no qualms shooting this NIB Maxi.
I wish I would have tried your load with 18.5 grains. I honestly don't know where I got my 13 grain load from. It must have been from one of my books. I'll go back and check.