I know for a fact, cause I've seen them and touched 'em, they exist!
A shooter buddy was using them in 2007 at a match in Sask. on his 338 wildcat cartridge at 1000 yds. We even sectioned one on half on a mill one Sunday Coffee night to see how it's put together.
The shooter tells me this year they don't kill animals worth sh(t though. They pick them up and toss them good, or spin then to the ground good and fast, but the big deer or elk will actually get up and run after getting hit with one of these aluminum tips. Blood everywhere at the hit location on both the elk and the deer, but he figures the aluminum tip does not expand so it's a small holes in and out. The blood trail even stops after (neither got too far), like it has sealing itself up again.
I have one of these Aluminum babes myself, but it is one that was pulled and the tip got bent, so I just touched it up with a hand file. Wildcat also make a 250g Aluminum in .338.
Like all custom bullets they are expensive compared with say a 250g Hornady SP which the shooter says would have put both of these animals down for good with the same shots.
I think he said he tried the 300g on the elk and a 250g on a big deer. He also said he will never hunt with an aluminum tip ever again.
Below is a pic of the Wildcat Aluminum Tipped 338 (hand filled at the tip) on the shooter's 338 SDM up against a 308, 6mm-250 30 Degree Imp with a fired 105 on it(if you look close you will see the rifling), and a 6PPC