I tried to calculate drag for hyper velocity project using this paper for Sears Haack revolution body. Some parameters:
Diameter: 160mm (round number for simulating 155mm projectile)
Fineness ratio: 13.2, which means projectile's length is 2112mm
From the paper, the assumed wing area is 0.077 l^2 = 0.077 x 2.112 x 2.112 = 0.3435 sqr metre
From the Figure 15 in the paper, the total Cd at 2km/s is about 0.004
So total drag at sea level Fd = 0.5 x v^2 x ro x S x Cd
Fd = 0.5 x 2000 x 2000 x 1.23 x 0.3435 x 0.004 = 3380 (Newton)
From the paper, the volume of projectile V = 0.002655 l^3 = 0.025 m^3. Assume it is filled by aluminum, then the mass is about 0.025 x 3000 = 75 kg
So the drag is about 4.5 gee
On the other hand, there is an empirical formula for hypersonic lift to drag ratio
L / D = 4 x (M + 3) / M = 4 x (6 + 3) / 6 = 6. It seems that if the projectile is shaped as a good waverider then drag can be as low as 1/6 of its weight, assuming the waverider is the best shape for hypersonic lift to drag ratio.
There is of course the problem about scaling where mass is increased at cubed speed, while area only increases at squared speed. While I don't have an complete computational model of waverider to compare directly with SH body, but it seems at the first glance, the waverider can get much lower drag than even the most aerodynamic shape, 1/6g vs 4.5g.
So is it true that the waverider have much lower drag than SH body?