This is my new Sten. There are many other like it, but this one is now mine...

[Vincent]

The cartridge is always at rest when it fires...

Yes, in this the cartridge is at rest. But we are talking about the breech block, not the cartridge.

if it wasn't then why would chamber depth be critical?

In my limited experience with blowback SMGs the chamber depth is not very critical. There’s no headspacing.

If you run a ream in and deepen a chamber by a few more turns your weapon will no longer function...

Most of the blowback SMGs I am familiar with have short chambers that leave quite a bit of the cartridge case unsupported.

I have made just about every mistake you can think of while making guns. One was to use the spec for a semi-auto that has a much deeper chamber than the full-auto version of the SMG. To my surprise, it shoots fine.

API is balloon juice...theory...

I never thought of it as a theory, just an application of Newton’s laws of motion.

There’s a mathematical analysis in volume 4 of George Chinn’s book “The Machine Gun”. https://www.milsurps.com/content.php...eorge-M.-Chinn)

My first experience converting an open bolt SMG to closed bolt didn’t go well because I didn’t really understand Newton’s laws of motion. I didn’t know a considerable amount of mass needed to be added to the bolt when going from blowback with API to plain blowback. I was lucky. The lugs on the buttstock stopped the endcap from hitting my face. After doing some research I added more mass (we can just call it weight) to the bolt, a stronger return spring and all was good. That experience made me a believer.

I can also attest to the rule of not adding water to a big tank half full of concentrated acid… a TIG welder can give you a nasty electric shock… sneakers will not protect your feet if you’re welding and a big globs of molten steel fall on them… pulling the handle down on a drill press really hard can make the drill bit snap off and it can go a long way into your forearm… if you’re extending the prongs on your wife’s Taser, it’s a good idea to take the batteries out first… a Taser (like the one my wife has) really can make you wet your pants… you don’t need a lot of gasoline to start a bonfire.. don’t fall asleep on the bank of a drainage ditch if you’re hunting hogs at night, big poisons water snakes really will try to stay warm by snuggling in with you…

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