Wartime, home made silencer

[Peter Laidler]

My uni mentor and later very good friend Prof Mike Hxxxxxxx and I did some research into silencers while writing the Sten book, using the student facilities here at the main lab on the Banbury Road here in Oxford. It was really about why the Sten silencer, developed by the National Physics Lab is still regarded as probably the best and still regarded as the yardstick by which others are judged. Woodsy is dead right in that the silencer casing MUST be able to absorb the total amount of gas generated by the fired propellant. The problem in ascertaining this volume of now uncompressed gas seemed insurmountable but true to form, he'd worked out a way of getting the answer. Not mathematically/theoretically but actually using an ingenious method he'd last used at senior school in York! Anyway, we worked it out that as a rough guide, the volume of air space in the silencer (excluding the baffles etc etc don't forget) should be 20 volumes of the barrel. Forgive me if I'm slightly wrong as I'm spouting this stuff from memory. We also established that because the gas exits the muzzle at 29 degrees (nope, professor Venturi had already worked this out for us. It's not 30 degrees nor 28, but 29!) there can be nothing between the muzzle and a direct line drawn to where............ anyway. It all gets complicated when you have a vented barrel of course because then, there is already pressure building up BEHIND the muzzle - which George Patchett solved.

Dr Philip Dater a US specialist used to visit us fairly regularly and was always a most interesting person to speak to. I wish he could have spoken to Prof Mike as they were both physicists who took the mystery out of the subject by using plain language. For example, when talking about a sudden heat ring build-up, Dr Phil explained it by saying '......just accept that it is fxxxxxg hot' Well, you don't get plainer than that! Interesting thread