Papabear55 How did you make out on converting your Ruger #1 to 577NE ?The idea of a .577NE in a Ruger #1 is sheer madness, as some of the above have already stated.
I ran the math, in a Ruger #1 a .577NE is roughly going to produce 150-180lbs of felt recoil. Its 120lbs of felt recoil or more in a 13-14lb double rifle. Totally unmanagable. The gun wasn't engineered to withstand those forces. The throughbolted stock will be the first to fail. Selling it will be near impossible thereafter as its so misplaced.
A 450/400, .416 Rigby, or a .470NE would probably be the practical/functional/utility limitation of a Ruger #1 in my opinion. A .577NE isn't really good for too many applications. The primary application is for elephant where it would give an actual difference in performance over a .470 or .500 which are both sufficient in their own right. But then, if you're going elephant hunting you're probably not going to use a single shot anyway. So ignoring that use case, we're talking about Buffalo/Hippo and smaller. For hippo, small bores with brain shots are plenty sufficient. So that leaves buffalo. The accuracy improvements and flatter shooting make the 450/400, .404J, and the .416 the quintessential calibers for that duty. In that case, you can spend $1500 on a brand new or lightly used Ruger #1 in any of those three calibers. (the 404J would be a custom actually).
I have not been on AH for a long time.
I have to say that other posters are giving you some really dumb advice.
1. 577 NE does fit in a Ruger #1
2. #1 Ruger are noted for recoil? I have heard that many times before, it is a myth!
3. Recoil will be too much? Balony! If I tamed the recoil on my 577NE H&R Handi rifle you can sure do it with a Ruger #1. Use a heavy (very little taper) 27 inch barrel. The 577 likes a long barrel. Lots of powder to burn. Maybe add a little weight in the stock if you want. Get it up to 12 lbs. ( some folks like 15 lbs. but it's not necessary.) I have a 458 Lott. A moderate load ( 1,900fps.) in 577NE which is what I use, will kill a cape buffalo DRT most of the time with a proper bullet and won't be much harder to shoot than you standard weight 458 Lott. Bullet diameter and design is king.
I love my 577 NE single shot and have killed more buffalo with it. ( Check out the CEB 600 grain Raptor and 650 grain Solid) However, it is not the most practical conversion for the Ruger #1. You have to remove quite a bit of metal to do it. The 500NE is an excellent DG cartridge if you use the right bullet. Round nose solid bullets are not the best bullet inspite of all the expert advice on the subject. A 500 NE will kill a cape buffalo quickly with Cutting Edge bullets. Done it several time with mild loads. ( Also you don't need/want max loads in these big cartridges. They don't need max velocity.)
Another cartridge (wildcat) that would be excellent in the Ruger#1 is the .550 Express. They make a .550 Magnum but it is not needed. CEB makes excellent bullets for the .550.
I need to say that most posters are so clueless about DG bullets performance and recoil that I thinks it's pointless to even talk to them. ( Did You know that there are very few African PH's that have ever seen a cape buffalo killed a close range by a 577NE with a proper bullet. I have done it, as you know, and the Ph is usually very surprised with quick way it kills. I alway ask them if they or anyone they know has seen a 577 kill a buffalo. )
Here is a good source for info. B&M Rifles and Cartridges. These guys designed an excellent DG bullet which is manufacture/sold by Cutting Edge Bullets and NorthFork Bullets. Sam is the 577 guy and Michael is the innovative designer for bullets and cartridges. The are not conventional thinkers unlike most gun cranks. Michael is into short cartridges and short rifles. (now there's guy who can handle recoil!)
Also if you still have your 458 Lott and want to enhance the performance just use cutting edge bullets. Just my opinion Good hunting.