Why do you need a knife as a back-up weapon?
If someone is close enough to grab your gun, or it is taken away from you in a fight wouldn't some unarmed fighting training be more useful? I could see carrying a knife for a tool, but not a weapon when you have a handgun already. If you really want a backup weapon, I say get another pistol.
PS Shouldn't this be in Prac Tac?
If someone grabs your weapon or weapon hand another "Clip" Magazine is useless.
If you ever needed to handcuff anyone while armed you would understand the need for weak side weapon.
The knife actually has many advantages over a second pistol as a retention weapon.
It has as much or more stopping power than any pistol.
It does take much more training but a trained man with a knife at contact distance is at an advantage over a pistol.
Basicly a pistol is a cordless drill that works at a distance.
Once the distance is gone it is at a disadvantage over a knife because of the limit of movement of the bullet coming out of the barrel.
A bullet only moves in a straight line.
A knife can cut 360 degrees.
The knife has great advantages when it come to weapon retention.
There is a leverage advantage against the man holding the pistol because you can grab the slide/barrel and jerk straight up breaking the wrist and finger of even the strongest and best trained man.
You can not grab a blade if you want to keep your fingers.
Against several opponents trying to disarm you a knife in a reverse grip is very hard to take away.
Once you've gained control of the direction of a pistols barrel it's easy to disarm.
If you know what you're doing you can disable the gun so even if the barrel gets pointed at you it won't fire,a weakness a knife doesn't have.
I'm not saying a knife is a better weapon,it's not.
Distance is a GREAT advantage.
Unfortunatly some jobs require you to deal with security risks at contact distance.
At this distance a knife can have an advantage over a pistol.
The brain is the weapon.
Everything else is a tool.