The link old4X4 posted has a lot of information. But I can tell you from first hand experience, I love the 416 Rigby on my Encore. I took a Water buffalo at 135 yards with a single shot with a 300 gr. Barnes X bullet. I have the gun sighted in at 1 inch high at 100 yards and it is topped with a Leupold VXII 1X4X20mm scope. I also installed a simms pad and a mercury recoil reducer in the stock. I had to drill the stock to install the mercury recoil reducer. I love the 416 Rigby round so much that I just bought a CZ 550 Safari Magnum in 416 Rigby. I want the option of a single shot or a bolt action.
The only draw back is the price of ammo. If you reload it is not so bad, but factory rounds are about $120.00 for 20 rounds. I bought 50 Norma cases from Cabalas for $94.00 and Barnes 300 gr. X bullets. Once I got it sighted in, I bought 20 more cases to reload. I went to Cabalas the other day and got another 50 cases because I want to work up a load for the CZ 550 Safari Magnum. I am hoping the loads I have for the Encore will be as accurate in the CZ, but if not I will have the cases to work with.
You won't regret getting the 416 Rigby barrel, I know I don't.
:-D
Also Cabalas is the only one carrying the 416 Rigby barrel, it is a Cabalas exclusive. Let us know if you get it and how it performs for you. If you want any other info, let me know and I will see if I can help.