I believe you could get definitive answers about this from SSK Industries which converts a lot of No. 1's to big calibers.



Here's a quote from their website:

Quote:

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Ruger 1: A fine rifle with great potential. Customizing with the caliber of your choice increases serviceability. Re-barreling can only be done to the same basic contour as the original rifle has. That means a 458 size barrel to go to any of the larger calibers which encompass the 50 x 3 1/4" (750 BMG bullet), 577 nitro or the 600 JDJ(577 nitro blown out straight to use the 600 nitro .620 diameter bullets - yes, this does require ATF approval - we have it). Arrestors and hydraulic counter coil recoil reducing devices are highly recommended in these larger calibers. High velocity screamers also work in the #1.

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Recutting the threads is not the issue with going to a larger round, especially in a #1.

the "thread" issue is the question of "is there enough metal left between the case and the threads, in the barrel, to hold it in"

Some of the rugers may hold a 577 (i understand that some of the early #1 had a thicker barrel shank, but I don't know.)

Saeed has one in 460 weatherby

500 NE is done "all" the time.

if you do do a .500, go with the 500 NE, for extraction and pressure reasons

jeffe

I did a Number One a few years back for a customer in .460 Weatherby. The fit with the 1.000 X16 threads wasn't a problem but I had to remove some of the top of the breech block so I could load the large diameter cartridge. When the breech block was in the lower or open position it didn't drop down far enough.

The .460 was about the Maximum diameter cartridge without reworking the receiver loading channel behind the breech block. Another issue that needs to be address is the safety. The larger diameter cases after firing, when ejected hits the safety. The case remains in the loading channel. To solve this problem, make a new safety and recess it into the receiver.

Another issue with a Number One is that it's an investment casting. If you do any welding on the receiver, you might run into an air pocket at any time. Some people like to weld up the safety slot and move the safety back on the receiver. If you do weld, make sure you use a tig welder. If you run into an air pocket STOP. You really don't know how big the pocket is and if it's a large one the action will start to feed in on itself.

For some reason Ruger heat treats a Number One receiver to about a rockwell 55 on the C scale. Tool steel starting at 60 on the C scale. If you try to recut the threads to make a larger barrel shank, send it out and have the receiver annealed. Send it out to Blanchard Metal Processing in Salt Lake City for both annealing and reheat treating. Sometimes customers like to have a Number One engraved, my engrave won't tounch one that hasn't been annealed.

Thanks for the input guys.
The rifle is a 1977/1978 model. I have just got it, I bought it fore the sole purpose of rebuilding it to a large calibre boomer.
I agree that the smartest thing would be to go with a rimmed cartridge, and that is probably what I end up doing.
The safety is an issue that many people are concerned with, I was planning to mill down a slot, maybe 1-2mm deep, manufacture a new safety witch don�t protrude as high and far forward as the original.
If necessary I will rework the receiver channel.
I have access to a well equipped machine shop.

What barrel manufacturer would you guys recommend for a 500 calibre.
I would like to have a Chrome Moly not SS.