200 THE COMPLETE WILDFOWLER 
As far as the shooting of guns converted on this principle is 
concerned, we can speak of one we know which shoots very 
well and has done some good work. We cannot enter into 
any details of cost of conversion of punt-guns, this matter 
being entirely one of where and how the work is done. We 
can add, however, that B.L. punt-guns when new are expen- 
sive. Old M.L. punt-guns are, as a rule, to be bought very 
cheap. The extra cost of conversion added to the price of an 
old M.L. gun would hardly reach half the amount charged for 
a B.L. gun of its size, new. 
The method of conversion here adopted is the simple 
screw-block breech. The M.L. gun is cut as near as possible 
to the breech. All wood and fixtures in the shape of hand- 
stock and hoops are removed. If the gun has trunnions, these, 
of course, can be left in the same position on the gun, for the 
conversion will make no difference to’ them as far as balance, 
etc., are concerned, which can easily be adjusted afterwards. 
The breech of the gun is then threaded and the chamber bored. 
The chamber has a slight taper. This is of note, and prevents 
cases sticking after being fired. Then the gun is ready for 
the breech-block to be fitted. If the barrel is to be re-bored, 
the boring can at this time be undertaken. The threads of the. 
breech-block are, perhaps, the most important items in our 
subject. They should be in shape exactly similar to those in 
our sketch, i.e. with wall back and tapering fronts. Such a 
thread is known as the ‘‘buttress” thread. The great advan- 
tage of this screw for the breech of B.L. punt-guns is that it 
may be always slightly slack, and yet, when the pressure of 
discharge comes on the block, the threads are tight. After 
the gun has been fired, the screw is again free to turn quite 
easily, and as this screw is to perform an important part in the 
extraction of the fired cartridge, it is essential that it should 
not jam, as it probably would do with ordinary V threads. 
The thread in our sketch is of % in. pitch. The gun is 
