Thread: Shotgun-9mm thing

If you have a half decent lathe you'll be able to cut a thread on it. Just get a good lathe book and nut it out, tooling is usually the expensive bit if you don't have any, if you need anything like that done I have a mate here who has a lathe and mill setup at home and could do it.

So the highest of the highest I have found in my data is 11,300PSI-12G and 61,500PSI-.308

I dont have sub sonic loads for .308 so will have to wait until I get on the computer to have a look for that. Also don't know the other bit so will also wait till I get on the pc and google it

Well that will go well!

I hope subs are better. I don't think a full load is bad either as its in its own barrel if thats right?

Hint, work out the area of each case head.............................PSI stands for Pounds Per Square inch.

Originally Posted by veitnamcam

Hint, work out the area of each case head.............................PSI stands for Pounds Per Square inch.

And the calculation Toby should be simple for a fellah like you. Just remember Big Ben Pies are Square.

Hopefully I've got this right

area for 12g - 0.6165"
"""""""".308-- 0.1750"

I can't do the litte 2 off my phone to show its sqaured

So thrust or pressure applied to the action for each is?

I googled and can't find a formula for that. Do you know one I can work off?

Originally Posted by veitnamcam

So thrust or pressure applied to the action for each is?

VC you are subtly becoming quite the physics teacher. Keep it up and Toby will thank you for it one day.

Starting to think me ditching physics for computing was a silly move on my part

I found this

http://en.wikipedia.org/wiki/Bolt_thrust

Also got the formula



6.96645 is a number I got for the 12g but have a feeling it's wrong and if it is right have no idea if it's N or lbs

Originally Posted by Toby

I googled and can't find a formula for that. Do you know one I can work off?

Its pounds per square inch so

12g - 0.6165" x 11,300psi = 6966 pounds of force trying to break the action apart
.308-- 0.1750" x 61500psi = 10762 pounds of force trying (and possibly succeeding) to break the action apart.

So we can see its in the bad idea bucket to run max power 308 out of the shotty action.

If we take 6966 pounds of force as max and divide by 0.1750 case head diameter we end up with 39,805psi as max safe pressure.
This is right around starting loads for 150gr in 308win.
Data I have here for cast bullet loads(that you cant boot up the arse cos they are too soft) Is 170gr 2000 fps =37700psi, 1600fps= 21600psi.

So it should be safe as houses subsonic or at reduced loads, the issue is making sure it is(if it was made) never fired with a full power load.

12g case head roughly 1.9cm diameter.
1 inch = 2.54cm
1.9/2.54=0.748 inches

Area of a circle
A=pi x r^2
pi x (0.748/2)^2 = 0.439 in^2

12g case head about 0.439 in^2

0.439 in x 11300 psi = 4966 pounds bolt thrust

It only be for subs. If I wanted a full .308 load I'd use the .308

So my calculation is right by vc and wrong by banana? I got the measurment off chuck hawkes which is different to bananas

I dont have one to measure but a quick google suggests 6-7k pounds thrust for 12g