Attentive readers will instantly recognise that this is the air rifle on page 159. Inattentive, or fiscally prudent, will have been wise enough not to have bought the book (which book, pray? Why, http://www.iop.org/EJ/article/0031-9120/41/3/M02/pe6_3_m02.pdf?request-id=6fe6bca2-f28b-4f25-a81a-9dfae4f8e0ac, of course. But don't click on that link cos it's a PDF, and I only include it because it flatters my pathetic little ego) so they won't have a clue.What you're looking at is a copper tube with a smaller diameter rifled copper barrel running down the middle
. The front is sealed round the outside of the rifled barrel, and traps air between the outer and inner tube. Air is pumped in using a bicycle track pump via the Schrader valve, soldered in the middle (to a ring of brass, also soldered in place, to give it a bit of purchase). It's sealed at the back by the brass valve which I have very kindly pulled out of the back (at the bottom of the picture) to show how it works. The smaller diameter O-ring seals the back of the barrel, and the larger O-ring seals the entire back of the outer copper tube. Pump the bally thing up and this brass plug tries to move backwards under pressure, and you hold it in place with some kind of improvised trigger at the back, which is what the steel rod is all about. As soon as the smaller O-ring clears the back of the barrel, all the air belts the bullet out down the bore. Should this explanation have you faltering then there is the option of thrusting money at your bookshop or my publisher, which they and I will enjoy, and you will ever afterwards regret especially if your local constabulary disputes your need to inform yourself of these arcane adventures in physics. - I digress. - (But how else am I going to sell the wretched book? I'm not J K Rowling for goodness' sake.)This particular gun has an 18.5 inch barrel, and since performance relates to the square root of the barrel length, the pressure has to be fairly high. (Because performance relates directly to the pressure.) Unfortunately copper ain't very strong, and if you get carried away, the outer tube will burst, possibly around 380 psi, and you will be horribly injured in a spectacular way because compressed air is incredibly (I choose the word carefully) dangerous. - The bigger the diameter reservoir tube, the lower the pressure it will tolerate. This one's 3/4 of an inch in diameter and I've had it up to 250 psi using one of those tiddly little air shock pumps, whereat it gave me a satisfying 260 feet per second velocity with a half-ounce lead ball, which since it's 33 foot-pounds is something you May Not Do in England.
. The front is sealed round the outside of the rifled barrel, and traps air between the outer and inner tube. Air is pumped in using a bicycle track pump via the Schrader valve, soldered in the middle (to a ring of brass, also soldered in place, to give it a bit of purchase). It's sealed at the back by the brass valve which I have very kindly pulled out of the back (at the bottom of the picture) to show how it works. The smaller diameter O-ring seals the back of the barrel, and the larger O-ring seals the entire back of the outer copper tube. Pump the bally thing up and this brass plug tries to move backwards under pressure, and you hold it in place with some kind of improvised trigger at the back, which is what the steel rod is all about. As soon as the smaller O-ring clears the back of the barrel, all the air belts the bullet out down the bore. Should this explanation have you faltering then there is the option of thrusting money at your bookshop or my publisher, which they and I will enjoy, and you will ever afterwards regret especially if your local constabulary disputes your need to inform yourself of these arcane adventures in physics. - I digress. - (But how else am I going to sell the wretched book? I'm not J K Rowling for goodness' sake.)This particular gun has an 18.5 inch barrel, and since performance relates to the square root of the barrel length, the pressure has to be fairly high. (Because performance relates directly to the pressure.) Unfortunately copper ain't very strong, and if you get carried away, the outer tube will burst, possibly around 380 psi, and you will be horribly injured in a spectacular way because compressed air is incredibly (I choose the word carefully) dangerous. - The bigger the diameter reservoir tube, the lower the pressure it will tolerate. This one's 3/4 of an inch in diameter and I've had it up to 250 psi using one of those tiddly little air shock pumps, whereat it gave me a satisfying 260 feet per second velocity with a half-ounce lead ball, which since it's 33 foot-pounds is something you May Not Do in England.
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