liner Lock vs. Frame Lock
Author: Brandon Uhl
Liner locks do not get a lot of respect at the moment, but I feel that well made liner locks are very solid and reliable. I find it strange that the frame lock gets much more respect despite the fact that the two lock types are very similar. I understand the advantages of the frame lock (and will outline them here), but in the end I think the difference is fairly small.
The liner lock was designed by Michael Walker, a custom knife maker who creates fantastic artsy tactical knives with unique locking systems. The liner lock caught on because it was simple to make (while many custom/unique locks are not), simple to use, and effective. However, liner locks are not simple to get exactly right. So many lower-end knife makers use liner locks (which are easy to make), but execute them poorly. This has caused the many stories about liner locks failing. The mating between the lockbar and blade tang has to be just right, and not many companies can get it just right.

The Spyderco Military is a liner lock knife that, as far as I know, has no reported failures. Sure, any lock can fail, but the Military is known as a very reliable knife with a liner lock that should not strike fear into your heart (or fingers) when you use it. On the other hand, there are some brand-name liner lock knives that do have many reported failures.
With any lock it is a good idea to do a light-moderate spine wack test (against something hard) to see if the lock will fail. Of course, do not do this test in a manner in which you will be cut if the lock does fail.
Chris Reeve invented the frame lock (also known as the monolock). It is similar to a liner lock, but their is no superficial scale on the lock side, so the lock bar is part of the handle (or scale) instead of part of the liner. The advantage is that the lockbar can be thicker (given the same overall thickness of the knife), and that your hand is wrapped around the lockbar naturally, which helps keep it from slipping.

However, there are not many reports of frame locks slipping during spine wack tests. There *IS* a lot of anecdotal evidence of liner locks slipping. This indicates that there must be a difference in the execution of the locks, since the design is essentially the same (especially during a spine wack where the hand is not holding the lock in place). Perhaps it is because framelocks tend to be found on higher-end knives, while liner locks can be found on countless flea market knives.
In the end, a good lock is a good lock. This is more a matter of the execution on the particular knife in your hand than the style of lock it is. One Military might have a super solid liner lock, while another might have been ground slightly different and is less reliable. That is why you should test *YOUR* knife rather than going purely on stories and anecdotal evidence.