"Who makes a 725 grain round for it? The biggest we have is a 440grain hard cast."
I designed over a dozen different cast bullets for the 500 and had molds made.
My designs all have noses .700" long for maximum net case capacity in weights of 400 to 725 grains. The 400s can be driven over 2000 FPS at safe pressures, the 725s almost 1200.
Go to
www.mountainmolds.com and use their online design page.
Here are the specs you want for a VERY accurate bullet that will give you more power than you'll ever need:
Bore riding design
.700" nose length
.100" Front band length
.200" Bore ride length
70% meplat
Weight in wheelweights your choice anything from 425 to 650 grains.
Choose the version with the most number of lube grooves.
You will be able to get the most energy from lighter slugs (like the 425 grain) as they put less shank in the case and allow more case capacity.
Every .100" increase in shank length reduces achievable muzzle energy by about 250 foot-pounds in the 500 at 60K PSI. A 425 as described above has only .200" shank in the case and can be driven over 1900 fps safely with WC680 powder in an 8 3/8" gun for 3500 foot-pounds of energy. A 650 grain bullet with the same nose has a shank .625" long and will thus reduce case capacity about 35%. A top load with this 650 will be about 1325 FPS for a bit less than 2300 foot-pounds.
These are top loads. My preference is 500-550 grain bullets at 1350-1400 fps for general blasting as the recoil and concussion are less taxing.
When I'm too lazy to cast I shoot uncannelured Speer 325 grain HPs designed for the .50 AE. Crimping straight into the jacket with .200" shank in the case I'm getting 2100 fps in 8" barrels with not-quite-max loads. VERY accurate and flat shooting, with not too much recoil. When you touch off one of these thunderbolts you will get the attention of everyone on the range. Shooting these out of the new 4" version feels like someone flicked on a heat lamp for 3/4 second.
Enjoy.
JR
P.S. I haven't measured the new Taurus 500 but its cylinder is definitely shorter than the S&W (about .200" shorter) and bullets with .700" long noses WILL NOT WORK in that gun.