The claim that you can get a bit more powder into the casing while seating the bullet to the same OAL as other monometal bullets is also true.
The only way that's true is if they're putting more bullet weight outside the case, and that would be from nose design, not the hollow base. Doesn't look to me like the nose is designed that way though, given the bullet shape. The hollow base does nothing to increase powder capacity compared to the same weight with a solid base. There still has to be that same volume of copper inside the case, regardless whether it's a short solid base or a longer hollow tube, or triangular with a picture of Elvis inside. The only thing a hollow base does is make the bullet longer for more bearing surface or boat tail.
I took a look at their 6.5 Grendel bullets, and am super skeptical about some of the claims as well. There is no way that 118gr hollow point has a .501 G1 ballistic coefficient. Not a chance. Compare that to Hornady's 123gr ELD, which is a MUCH sleeker bullet with a finer tip, more weight than that 118gr, and field-proven ballistic coefficient between .496-.510 G1 depending on the gun and other details. The 120 SGK and 120 TSX are only .421 and .386 respectively; I think a realistic number for that 118gr would be closer to those, and at least lower than the 120 SGK.
These certainly might be decent hunting bullets, but it's wise to be skeptical of claims that are over the top like many on that website. Seems to me that they've implemented some very generous marketing, at best. Over selling stuff like that is way worse than underselling IMO; it means you're willing to lie to me to make a buck, AND think I'm too dumb to figure it out.
