Hi to everyone here. I have been lurking here for a few years and first want to thank everyone here for all their knowledge throughout the years. My scorpion project would of never gotten done without all your help.
Now to a few observations about the OOB(out of battery) kabooms that have been reported. First, from all the reading I have done, it seems to be no more common than on the MP5 platform, and a bit less than on the blowback AR 9mm platforms. Those two platforms DO have one big advantage over the Scorpion when a OOB happens: they are metal in the receiver. A OOB in them usually blows out the bottom of the magazine(not ALL the time, but a bullet can lodge in the barrel...) and you clear, dump the mag, check the barrel, bore and chamber, and start over. With the Scorpion, the left side of the receiver can blow out(usually? Blow out...) and it's to the mothership or gunsmith or writing off the Scorp. But why does it happen in the first place on the Scorp? From my reading I found that one case was a slow fire on semi-auto that killed it in the first few shots. A few implicated bump-fire, binary-triggers, and/or bad ammunition.
My take on this starts with an observation: open bolt blowback 9mm sub-machine guns slam fire with a firing pin machined into the bolt face. They can have an OOB for a few different reasons: dirty chamber with a partial obstruction, etc., seems reasonable. The UZI, M1A1 Thompson, MAC all do this. BUT when it does happen to them the metal in the receiver contains most of the explosion(sidebar: the machinegun Scorpion A1 is closed bolt with a safety auto sear that physically holds back the hammer until the bolt is fully forward, and only then can the hammer fall-and it uses a striker unlike the afore mentioned sub guns). I couldn't figure why or how the Scorp S1 could KB at all even if it slam fired. If the bolt is closing, the round is going into the chamber, but the extractor has not grabbed the cartridge yet. That happens as the mouth of the cartridge stops in the chamber, the bolt keeps going forward, the extractor snaps over the cartridge, and the cartridge now is being held to the bolt face. Theorizing this is essentially the same as the UZI or M1A1 but without the firing pin actually being proud of the bolt face at this time. So, even if the hammer should strike at this exact moment it should be fine? So what the heck is happening? I read one post that said something that made a lot of sense: bolt bounce. If the bolt goes through all the above, then bounces back slightly, the cartridge is still held firmly to the bolt face, if the hammer is just behind the firing pin and hits the firing pin detonating the cartridge, and you have a OOB, which might be a KB also. I personally think that is a partial answer. There are also some 9mm rounds that are a little longer than others, weaker 9mm cases, etc. And I think bump firing is a huge risk: the gun is held looser than normal and that affects the harmonics and dwell time of the bolt speed in relation to the chamber, and that can affect if there is a bounce and how much there is. I also think that Binary triggers are not that much of a danger: the A1 sub gun shoots at 1150-1200 Rpm, and the fastest i have ever gone with a binary trigger was around 600 Rpm. I feel this makes a binary trigger as safe a any on this platform, YMMV.
Now lastly: the firing pin block. A lot of writing has stated that the block is faulty, allowing an OOB. Now, a few of them have not been working properly and there are lots of postings on how to check and or fix the issue. But one thing I strongly feel is that the block is NOT to prevent an OOB, its not designed for that. It is a drop safety only. Now I know that is an unpopular opinion, and I get that. I too wish that BATF had allowed the safety sear to remain in the S1, but there is nothing we can do about that. As an aside, the Fostech binary triggers for the AR-15 and AK-47 both have a safety lever that only allows a hammer trip after the bolt is fully forward. But that one is not fully Automatic: the hammer only can fall if you pull the trigger after the bolt is fully forward. If pulled too early you have to pull or release the trigger again to get a shot off. CZ and the binary trigger guys(Franklin I'm calling you out on this...)could/should do this to make the gun safer.
As usual, this is all IMHO, and YMMV. All opinions are welcome here, as I'm SURE I missed something here.
