THe 500 A2 is a 460 WBY blown out to .50 caliber. There are a few versions of it out there but A-square and the .510 wells are essentially the same thing. This is one mean cartridge . You can drive a 600 gr bullet at 2500 fps with IMR4064. You can throat the chamber so that you can load and shoot 650 gr .50BMG ball or 750 gr Hornady A-max's. It's got tremendous versatility. Based on what you have to do to open a Enfield up to a .416 Rigby, why not go for a 500 A2 instead. On a CZ550 basically you can order a pre threaded short chambered barrel in 500 A2 and be in operation in about 2 hrs. It takes very little experience to make a CZ550 that starts as a .416 Rigby action into one. I've built a couple of 500 A2's and they are slick. Look in A-squares manual for more information.-Rob