You are missing things, like a feel for magnitudes of numbers.
0.2 inches is almost a quarter of an inch (0.25"). Your pressures might be thousands of psi (35,000 psi, I'd write ksi or kpsi).
One must carefully differentiate between nominal and actual dimensions, look to the engineering drawings of the bullets.
All of the bullets mentioned, and pressures, are very similar, but the devil is in the details. ETA - read how SAAMI pressures are actually measured.