Weapons held by other players have inconsistent deflection properties.
For example, a Protector 9mm will deflect approximately 55 bullets, at which point all Protectors from there forward lack any sort of damage mitigation or bullet deflection properties. Rather than provide a consistent deflection experience, any shots beyond those initial deflections will be full damage shots.
On the other hand, a CAR-95-1 will deflect 5 or 6 bullets, at which point the weapon ceases to provide defensive benefits. This is representative of the higher penetration value on the weapon's ammo, but does not explain why the gun stops providing deflection capability for no apparent reason. It isn't like the gun stops functioning, it simply won't block incoming rounds anymore.
This sort of inconsistent player experience is detrimental to the community as a whole, and can lead to frustrating incidents where one person has a weapon that deflects things and the other person's weapon does not.