The blow back or cam system have ways to allow the chamber to open after pressure is released by the bullet. The pressure rapidly decreases after the bullet exits the barrel.
Which is more reliable? Both have been around for years and probably will be around for more years.
The Hi-Point handguns use the physics of more energy needed to move mass. The PPK uses springs (recoil and main). The 1911 (and others) use a link to keep slide and barrel together until pressures decreases. Others use a camming system.
Comparing two different .380s (one a PPK/s, the other is a Kel-Tec P3AT), I have found that, for me, the PPK/s is more accurate.
Comparing my H&K PSP P7 (blowback) to a clone of the Browning Hi-Power, they both are reliable. And depending on ammo, the accuracy is not much different (I did some work on the BHP clone before this).
I would not worry about which is more reliable in making your decision. If the firearm was not reliable, it would not stay on market too long (except the dern Jimenez/Jennings pistol).
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
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Former President of the ECPT (Eifel Combat Pistol Team)