Hornady 300gr FTX has a BC of .200. Barnes has a 325gr and 375gr with BC's of .228 and .261.
http://www.hornady.com/assets/files/ftx_load_data/500_sw_magnum_ftx.pdf
Even if it doesn't expand it's not going to matter much. But I'm betting you'll get some expansion.
Out of a rifle I'd use one of those. I can't say I'd want to shoot 500gr bullets of a rifle; that would hurt.
I have shot two deer this year using a rainier 350 gr HP bullet. I used titegroup about 14gr,(which my gun loves) and went through one side and out the other...I think the stated combo is rated at like 1400 fps, but NO recoil at all. Granted I would not shoot this load past a hundred yards, but both my deer were around 75 yards and no problems at all.
My first instinct is to say he gut shot it. But I wasn't there either....I have a friend that says he shot one with a 500S&W Handi and it went down, got up and ran off. No blood to trail either! Now, I wasn't there so, this is just hearsay so......Don't shoot the messenger!
no offense taken, but the op wanted a load with a gun that he already has...which is a .500. He was also looking for a long distance load, which usually is a high recoil load of lil gun or h110. The thing about my load is that it is a reduced load that feels like your shooting a .357. With this load you don't want to shoot it past a hundred yards because it will drop like a rock...No offense, but at 75 yards, does it really matter? My daughter took her first deer 3 years ago at ~80 yards with an old Model '92 in 44/40. If your shots will be less than 100 yards, anything from the 357 Magnum carbine on up will do just fine. Shot placement is still everything, even in this discussion.
I have a friend that says he shot one with a 500S&W Handi and it went down, got up and ran off. No blood to trail either! Now, I wasn't there so, this is just hearsay so......Don't shoot the messenger!