Here is the issue when i tested it the pistol autofire was faster on 60ticks, current method makes the convars inconsistent because of framecounting when game's tickrate is altered.
PHP Code:
l4d_weapon_auto_fire_pistol_frame "3"
Translates to at default tickrate @30
Next auto fire = GetGameTime + (0.033 * 3)
At tickrate @60
Next auto fire = GetGameTime + (0.0165 * 3)
Formula
GetGameTime + (GetTickInterval * 3)
If you had bugs using gametime you are using it wrong, gametime is how weapon firerates are calculated internally and nearly everything else bound to a tick.
Edit:
In any case you know how a tick works, I simply wanted to help you by informing you how a tick works and it's not always same tickrate you will deal with most people how no idea that it can affect plugins like this.