While I'm sure the 7x57 was influenced by the Gew.8mm of 1888 it certainly isn't an 8x57(.318'') necked down to .284''. The 8x57 mm with .323'' bore wasn't adopted until 1905. The 6.5x55mm Swede (1891)actually predates both the 7x57 and the 8x57JS(not the 1888).The 7x57mm Spanish Mauser cartridge
arent case none
Case type Rimless, bottleneck
Bullet diameter 7.24 mm (0.285 in)
Neck diameter 8.25 mm (0.325 in)
Shoulder diameter 10.92 mm (0.430 in)
Base diameter 12.01 mm (0.473 in)
Rim diameter 12.10 mm (0.476 in)
Rim thickness 1.15 mm (0.045 in)
Case length 57.00 mm (2.244 in)
Overall length 78.00 mm (3.071 in)
Case capacity 3.90 cm³ (60 gr H2O)
Rifling twist 220 mm (1 in 8.66 in)
Primer type Large rifle
Maximum pressure 390.00 MPa (56,565 psi)
8x57 mm Mauser cartidge-Designer German Rifle Testing Commission
Designed 1903/1905
Variants 8×57mm IRS (rimmed)
Specifications
Parent case M/88
Case type Rimless, bottleneck
Bullet diameter 8.08 mm / .318 (I and IR) and 8.20 / .323" (IS and IRS)
Neck diameter 9.08 mm (0.357 in)
Shoulder diameter 10.95 mm (0.431 in)
Base diameter 11.94 mm (0.470 in)
Rim diameter 11.95 mm (0.470 in)
Rim thickness 1.30 mm (0.051 in)
Case length 57.00 mm (2.244 in)
Overall length 82.00 mm (3.228 in)
Case capacity 4.09 cm³ (63 gr H2O)
Rifling twist 240 mm (1 in 9.45 in)
Primer type Large rifle
Maximum pressure 390 MPa (57,000 psi