Thank you for that great technical description, Peter. I looked for the high speed camera video on the NPL website. http://www.npl.co.uk/publications/videos/ They have some interesting videos. I couldn’t find the silencer one.
I did find this one on youtube that shows the expanding gas and the bullet traveling through a suppressor.
There’s some slow motion in this video of a Mk5 where you can see those smoke puffs coming out of the suppressor.
Unfortunately I can't see the video's you are referring to Vince. The atmospherics of the L43/Mk5 were truly emphasised on the video especially when the great Lt Col Mike Txxxxx was doing the teaching. It all made sense on the range later. I wish I remembered the saying we used about silencing weapons. Went something like '..... add different quantities of A level mathematics with some A level physics with some thing else........... Anyway.........
Glad you all liked the schoolboy explanation!
Incidentally, if yoiu do have an original Mk5/L34, the inside of the muzzle cap and front end of the extended tube do get a bit of a pasting so it's worth machining an exact copy from stainless and use that if you want the gun to last the course
Last edited by Peter Laidler; 09-30-2015 at 09:43 AM.
To be quite honest Peter, what I found with suppressors was there's a number of principles and factors that are involved...and as long as you don't violate any of them too badly things seem to work reasonably well...I never sat in class for any of it and physics facts escape me...mostly. That is until a student one day announced to me I was teaching physics in rifle class...
You should do a short vid when at the range next...? Both with subsonic 147s and with 115 ball. Just for yuks...
The difference between 147gr and 115gr is noticeable.
I am still working on getting this gun dialed in. The Israeli 158gr is fantastic!!! It’s the quietist 158gr I have tried so far and it’s reliable. Some of the commercial 158gr and 147gr have trouble getting the breach block far enough back to engage the sear.
All the brands of 124gr I have tried so far have been 100% reliable and quiet enough not to disturb the neighbors. (There’s no need to take this one to the range. It’s “backyard quiet.”)
115gr makes some noise. It seems to be from the breech and there was more gas blow back. It could also be the powder as I have only tried two brands. I have several options to add more mass to breech block, starting with the block, cocking, handle. If that’s not sufficient, there’s an unmodified breech block and/or a firing pin retainer from a Mk6 semi-auto. So there are several combinations to try. A stronger return spring is also an option.
I have a Chilean FAMAE PAF breech block that’s very light. We will see how it does with the 158 & 147’s.
Maybe I can get one of the kids to help me with a video after I have the gun sorted.
Speaking of A level math, I find the formulas in The Machine Gun by George M. Chinn very useful. They are handy for calculating things like breech block weights, throw and spring rates for blowback guns. I normally use them in a program that lets me adjust barrel length, bullet weight, powder charge, breech block weight, spring rate and pretention so the cartridge case is where I want it when the bullet leaves the barrel and the pressure drops. It works great with a normal barrel. But the Mk5 doesn’t have a normal barrel. The pressure starts dropping before the bullet leaves the barrel. So field testing is my only option. It’s not really a burden. I actually like being able to shoot in my garden and not be heard. And those garden gnomes are irresistible targets.
PM
Originally Posted by 
