Hi Tx635,
Dog or "ketch" locks were largely made and used by English gun makers. Brian Godwin, perhaps the most knowledgeable expert on these locks also calls them "type 2 English locks". They were England's answer to the French flintlock during the later half of the 17th century. They are sturdy, simply made locks usually with tumblers lacking a half cock notch, hence the dog catch. Being early, they have deficiencies. There is usually no internal bridle supporting the tumbler on the inside. The tumbler is supported only by its post going through the lock plate and the flint cock. That was an inherently weak arrangement that wore over time. The dog catch itself was not liked by soldiers using muskets equipped with them and they much preferred later versions that had half cock notches and then removed the dog catch. The thin cocks often broke. Also they usually did not have fences on the back of the pan allowing the wood of the stock at the breech to get charred from the flask of priming. Their advantage was they were cheaper to make than true flintlocks. Sweden and Norway also made military guns with dog catches late into the 18th century, however, I believe those locks had tumblers with half cock notches so the "ketch" was kind of over kill.
dave