RIFLE-BARREL STEEL, .30 CALIBER.	69
Specimens from Rifle Barrels, from Springfield Armory.
The specimens marked M3 D represent the steel in the bar.
Those marked M 3 A, M 3 B, and M 3 C, two sets, were taken from finished barrels, one set from the butts over the powder chamber; the other set were taken farther up the barrels, near the middle of their lengths.
Specimens carrying the letter A came from barrels which were annealed after roiling, according to the usual practice at the armory.
Those marked with the letter B were from barrels rolled and annealed at their residual heat, while specimens C were cooled in the air after rolling.
Hydrostatic tests of sections over the powder chambers were made on barrels from each of the three lots above mentioned, the results of which follow the details and tabulation of these tensile tests.
No. 7399.
Marks, M 3 D.
Sectional area .25 square inch. Gauged length, 1".
Specimen from the bar.
Applied loads per square inch.	Elongation per inch.	Successive elongation per inch.	Permanent set.	Successive permanent set.' ■».	Remarks.	
Pounds. 1,000 5,000	Inch. 0. .0001	Inch. 0. .0001	Inch. 0.	Inch.' (5 0.	; V V■ • >• •’ \ ; ;• >£7 Initial load.	
10,000	.0003	.0002				
20,000	.0006	.0003				
30,000	.0010	.0004				
40,000	.0014	.0004				
50,000	.0017	.0003				
60,000 70,000	.0021 .0025	.0004 . 0004	0.	0.		
75,000	. 0029	.0004			Elastic limit.	
76, 000	. 0058	.0029				
77,000	.0075	.0017				
78, 000	.0090	. 0015				
80,000	.0115	. 0025				
84,000	.0150	.0035				
88,000	.0190	.0040				
92, 000	.0230	.0040				
100,000	.04	.017				
108,000		.01				
116,000	.08	.03				
118,880					Tensile strength.	
						
General summary.
Tensile strength per square inch of original section.......................pounds.. 118,880
Elastic limit per square inch of original section..............................do... 75 000
Elongation per inch after rupture.............................................inch..	’. 23
Elongation per inch under strain at elastic limit..............................do...	.0029
Character of broken surface......................... fine granular 60 per cent, silky 40 per cent