STRESSES IN GUN FORGINGS. 
89 
The accuracy of the results is of course dependent upon 
the measurements of diameters. Of this, however, there is 
every indication that proper care and skill were exercised. 
The measurements were made with a micrometer scale and 
read to the fractional part of tofoo °f an iuch. The sensi¬ 
tiveness of the results is such that an error of joiroo °f an 
inch in the reading of an average diameter (five inches) cor¬ 
responds to 600 pounds per square inch in the expressed 
stress of tension or compression. 
Deductions from the Application of the Formulas for Gun 
Construction .—These and other similar experiments show 
the favorable condition of strains produced in a hollow forg¬ 
ing by interior cooling. The strains are analogous to those 
produced by shrinkage in the built-up construction and serve 
the same purpose. The present experiments are particularly 
instructive in that they deal with a hollow forging of vary¬ 
ing thickness of wall, with sectional dimensions correspond¬ 
ing to the service field gun. 
The strains directly produced by the treatment are found 
to be more intense than is necessary and show the desira¬ 
bility of an amelioration of that treatment in future opera¬ 
tions ; but the strains left after annealing the treated forging 
are moderate and satisfactory. The elastic resistance of the 
sections, both before and after annealing, is shown to be 
superior to that of corresponding sections of the built-up 
field gun. This, however, is in part attributable to higher 
qualities of metal. 
The physical qualities of the forging, determined from 
tensile-test specimens taken from it after treatment, are as 
follows: 
Breech end. Muzzle end. 
Elastic limit, pounds per square inch. 68,000 75,500 
Tensile strength, “ “ “ “ . 126,500 128,400 
Ultimate extension, per cent. 9.50 11.625 
Reduction of area, “ “ ... 12.14 16.35 
For present purposes the elastic limit for extension will be 
taken at a reduced value, 0 — 60,000, and the elastic limit 
for compression will be defined in each section by the actual 
