I'm due to update this guide soon, since J-Runner now has support for building RGH3 nands built in making this process lots easier.Wanted to say thank you for this guide. I was able to successfully RGH3 my Jasper BB last night and the results are pretty amazing. I'd say instaboot every 5 out of 6 boots and the ones that aren't instaboot are < 10s.
That said, I wanted to suggest a few additions to the tutorial that might help people new to the scene. I'm on the opposite side of things in that I modded OG/360's in college, but back then the only thing for 360s was DVD drive firmware patches, so working with the NAND is new to me and the JRunner instructions is mainly where I found holes that slowed me down.
In the section describing the ECC Files. Specifically around "Drag and drop the ECC File containing your board revision name to J-Runner and press Flash NAND"
It would be helpful to briefly clarify the difference between the Corona vs Corona_4G and Jasper vs Jasper64. I.E., on the non big block NAND jaspers you end
up with a 16MB NAND dump and therefore need to start with "RGH3_Jasper_10mhz.bin" vs if you have a big block 256/512MB NAND Jasper and end up with a 64MB NAND
dump you need to start with the "RGH3_Jasper64_10mhz.bin"
In the section describing how to build the RGH2 NAND. Specifically after "Once the console boots into Xell Note down your CPU Key and Input this into the CPU Key section in J-Runner"
It would be helpful to correct this screenshot and instruct the reader to load their retail NAND backups in the Load Source and Load Extra slots + their CPU key. As it is written and shown via the screenshot, the reader is likely to try this with the ECC file like I did. After the fact this seems silly, but without really understanding what's going on for the first time it can happen.
For the screenshot following "Use J-Runner to write the newly made RGH3NAND File to your Xbox by dragging the RGH3NAND.bin file to J-Runner as shown below:"
Emphasis could be added that the final step is to press the button "Write Nand" and that you'll most likely have to tell Jrunner which console you're flashing again.
Thank you again
I will leave the tool I created live though in case anyone ever wants to tinker in the future.