There are always going to be the 1% situations. I have read reports where the .38 round has failed. However when you look at the type of ammo used it all becomes clear. You have to use the right tool for the job. Using standard FMJ or cheap low grade ammo is going to get you low grade results.
Once you have picked your caliber, you need to pick the right round in that caliber. Ballistics mean something. You have to take into account that if you have to fire your weapon at someone it is a life and death situation for that person and it has been reported time and time again that humans possess can perform some amazing feats when their life is on the line. It all has to do with the makeup of the person in question.
As for your 340PD. I would advise against loading it with .357s. I have seen three blow up on the range. There are a couple of websites dedicated to the problem. Shooting a .357 out of a snubbie is over kill in my book, but if you feel it is going to help you win a fight if you ever find yourself in one, then by all means carry a way. I am nobody to be telling you how to live and preserve your life. To each is his own.
http://www.thegunzone.com/sw340pd.html I a little back ground about me so that no one thinks I am just some gun nut. I am a former police officer, I am still an auxiliary Deputy Sheriff for a county south of Atlanta. I only do this to keep my certification here in the state. My uncle is a Sgt with that same department. He has been assigned to the range as the dept range master, armorer and instructor. I have spent hundreds of hours down there with him. I have been able to talk to dozens of officers involved in shootings and watched hours upon hours of shooting and fighting videos from dash cams. This has been a valuable asset in insuring I survive a deadly encounter.
I have been lucky, not only do I have my uncle to help me sharpen my teeth, but the range is also shared by the county police and they have two of the finest range masters in the country. Between the three of them I have some of the best instruction money can by all for free.
I have always been into handguns, shotguns and sub guns. I am not a big rifle guy. I like the CQB stuff. I am not big into martial arts at all, but I do take Krav Maga because it incorporates firearms and it is based around close encounters.
I feel if you are going to carry a firearm day after day, night after night, to not only defend your life, but the lives of those around you, then you need to make yourself as sharp as possible. I feel it is the users responsibility to train and study, not in the hopes of one day being a hero or a tough guy, but as someone who survived or kept others alive though their knowledge.
There is a gun by me or on me pretty much all the time. If I have to use that weapon to protect myself, my family or some random person from harm I am going to make sure I have the knowledge and the skill necessary not to fail them or myself.
There is a county police officer here that has been in three shootings. He has only been on the job for five years too! One on duty and two off duty. He has survived all three. Ask him how he does it? Training. He even used a .22 to save the life of someone else in one of those shootings. It goes to show that with the right training and tactics (software) you can protect yourself or someone else without using a fire breathing, hand cannon or a supped up auto with extended slide release levers and extended mag release button, laser sight/flashlight and a giant Houge slip on grip wrapped around the grip (super computer hardware). People buy that crap because they think it makes the better, when it is in fact training that makes someone better.
This officer who has been in three shootings, spends a lot of time on the range. He is always asking for help to better himself. That is key, assuming you have all the answers in your first mistake. Asking for help to better yourself is a win-win situation. You get the help you need to better understand something and you make a friend.
I would advise Laz, keep an open mind when it comes to self defense. It sounds like you do at some level when you made the comment that something is better than nothing. Even the best firearms in the world malfunction. My issued Glock 22 malfunctions from time to time. It happens. You have to be able to roll with the punches, adapt and over come. It is not about winning, it is about surviving. Careful with .357s in that 340, not because I don't think you can handle them..I just don't want to hear about your frame cracking or weapon exploding on you. Stay safe.