As said above
Your cases need to be fireformed.
It looks like your 460 cases have been taken out to 510 but not fireformed to blow out the case if needed and establish the new shoulder.
This won't be an issue as the 500 headspaces on the belt not the shoulder as rimless rifle cases do.
As already said there is no real need to crimp but crimping may affect accuracy with some loads. Certainly not needed for fireforming.
I would suggest a minimum load at rocks. Great fun to be had!
I shoot a 500 Jeffery, which is a hoot, and would love to know how you go accuracy wise.
If you wanna swap some 440 grain Bertram SPRN pills for 600 grainers let me know.
As far as loads go I would suggest you look at Hogdons website and check the ADI equivalents.
Remember a too light load can be more dangerous than a too heavy one so fireform with the minimum load or TB.
Also found this out on
https://forum.accurateshooter.com/threa ... e.3742616/Here is what the A-Square manual shows for those three powders. I don't have any info for IMR-4198.
600 gr. A-Square Dead Tough bullet
26" barrel
Maximum Average Piezo PSI: 63,860
H-4895 106.0 gr. 2346 fps 55,300 psi Average
H-4895 115.0 gr. 2474 fps 61,600 psi Average
IMR-4064 112.0 gr. 2380 fps 52,000 psi Average
IMR-4064 117.0 gr. 2503 fps 61,300 psi Average
IMR-4320 110.0 gr. 2382 fps 59,100 psi Average
IMR-4320 115.0 gr. 2465 fps 65,700 psi Average, load exceeds max avg psi
Hope that helps and gives you a place to start with those powders.
Have fun
One well placed shot is all it takes.