I have both -- a custom Ruger SRH in .500 Linebaugh, and a BFR in .500 JRH. Love both calibers, but have to say that I am dumbfounded by the accuracy we are getting with the JRH. Here is a photo of a group I shot at 50 yards and I am not particularly good at shooting groups:
Here is a group photo of some .50 cals. From left to right, .50 AE, .500 JRH, .500 Linebaugh, and .500 Smith and Wesson.
The .500 JRH is indeed a production caliber on the BFR line now.