In recent years, there has been a general tendency to increase the caliber and power of naval and coast defence guns. At the same time, the fear becomes more and more manifest that guns of large caliber, on account of their increased power, may wear out prematurely and lose accuracy of fire to such an extent as to no longer meet the justifiable needs of service in times of peace and of war. Several examples of short life which have occurred in the naval and coast artillery of various countries seem to justify these fears. In view of such occurrences, it seems opportune to call attention to some endurance tests lately carried out by the Krupp Company at the Meppen firing ground with several of their large caliber guns of the jacketed and hooped type. The results of these trials furnish proof that, in so far as guns of the Krupp construction are concerned, the above mentioned apprehension is devoid of any foundation.
Two 8.27-inch naval guns, length 45 calibers, model 1901, and an 11.02-inch naval gun, length 45 calibers, model 1901, have, in the course of recent years, fired a very large number of rounds at the Meppen proving ground. Before each round, excepting in the series fired rapidly, the length of the powder space was determined by measuring the distance from the rear face of the loaded projectile to the supporting ring for the cartridge case bourrelet; since an excessive increase of the length of the chamber, due to wear and the erosion of the rifling lands at their origin, would entail a notable diminution of the initial velocity, and of the accuracy of fire, and consequently of fitness for service.
The indications indispensable for a judgment of durability, taken from the actual results of the tests referred to, are set forth in what follows, as well as in appendices 1 and 2. It is there shown that the two guns of 8.27-inch caliber have fired, up to the present time, 390 and 344 rounds, respectively, and the 11.02-inch gun, 192 rounds, without the muzzle energy and accuracy of fire being sensibly diminished; the limit of their lives, therefore, has not yet been attained, and the tests of these guns will consequently be continued.
KRUPP 8.27" GUNS OF 45 CALIBERS LENGTH, NOS. 1 AND 2.
(Light type, Model 1901, with jacket and two rows of hoops.)
DATA RELATIVE TO GUN No. I
Length of gun. 370.9"
Length of bore 347.5"
Length of powder space 55.4"
Length of rifled bore 292.1"
No. of grooves. 64
Twist of rifling 1 in 45 to 1 in 30 calibers
Weight of gun, with breech closure 33,369 pounds
Weight of projectile 238 pounds
Initial velocity 2,789 f. S.
Muzzle energy 12,850 f. t.
Gun No. 2 had a longer powder chamber (56.0-inch), on account of the reinforced rotating bands adopted for its greater power (mean initial velocity 2903 f. s., see also "Remarks" relative to Gun No. 2). The rifled part, consequently, is shortened to 291.4-inch. The number of grooves is reduced to 6o.
REMARKS REGARDING THE EXTRACTS FROM FIRING SHEETS AND THE DIAGRAMS OF POINTS OF FALL OF 8.27-INCH GUN No. I.
With the principal object of these trials, which was the determination of durability, were combined certain secondary objects, particularly experimentation with powders of different dimensions as well as with rotating bands of different forms and materials. The variations in initial velocities, for equal weights of projectile and of charge, must be attributed to this circumstance as well as to the lower temperature of the powder in the latter tests.
After the first 350 rounds, the initial velocity was increased from 2789 f. s. to 3084 f. s. in order to try the gun also with the normal power (15,690 f. s.) for which Krupp guns of this caliber and model are designed. Under these conditions, 36 rounds were fired.
In judging the resistance of the gun, account must be taken of the higher temperature of combustion, in comparison with nitrocellulose powder, of the powder with 25 per cent of nitroglycerine used in all the tests. It must also be taken into consideration that the greater part of the firings were concentrated in very short intervals of time. Among others, there were three rapid-fire series of ten rounds each, that is, rounds Nos. 231 to 240 in 2 minutes and 20 seconds, rounds Nos. 241 to 250 in 2 minutes and 25 seconds, and rounds Nos. 264 to 273 in 3 minutes and 3 seconds, which, on the average, corresponds to four rounds per minute.1 In spite of all these conditions favoring wear and erosion of the lands, the length of the powder space only increased 2.52-inch, or less than 1/3 a caliber, as the result of the 392 rounds fired up to the present time. This shows how great the resistance of the gun is, in spite of its great power. How small, thanks to this great endurance, the loss of initial velocity attributable to increased length of the powder chamber has been, may be seen by comparing rounds 14, 18 and 22 with rounds 214, 220 and 226, as well as rounds 54, 60 and 66 with rounds 215, 221 and 227. These rounds furnish a particularly good comparison for the reason that they were fired with powder and projectiles of the same kind and of the same lot. Only the temperature of the powder differed much, being 14° C. in the latter firings, or 13° C. lower than in the earlier ones. The first of these comparisons, where the length of the powder chamber had increased by the small quantity of 1.14-inch after about 200 rounds, shows a diminution of average initial velocity of only 86 f. s., and the second, where the length of the powder chamber had increased .95-inch after about 160 rounds, shows a loss of velocity of 90 f. s. And, moreover, it must be noted here that the greater part of these diminutions of velocity—about 66 f. s.—is due to a lower temperature of powder.
At round No. 386 a projectile weighing 309 pounds and 4 calibers long was fired to determine if the gun was still capable of meeting the requirements imposed by the forcing of so long a projectile. The test was particularly hard from the fact that the projectile was taken from the old stock of the proving ground and for this reason the form of its rotating band was not suited either to the great initial velocity or to the special conditions of loading. The trajectory of the projectile, nevertheless, was excellent (see the illustration of the perforations made in cardboard screens, placed 50 meters and 140 meters from the muzzle).
1In the extracts from the firing sheets, in Appendix 1, rounds 231 to 237 and 238 to 250 are grouped in series, because the former were fired with shell fitted with less-pointed caps, and the latter with more-pointed caps.
The diagrams of points of fall were chosen so as to permit a comparison at three different ranges, at the beginning, at the middle, and near the end of the tests thus far carried out. It may be safely concluded from them that the accuracy of the gun has remained beyond criticism. This is also proved by the last grand series of rounds, fired after the increase of initial velocity (rounds Nos. 375 to 385 at about 13,500 yards, having given a dispersion in range of 126.6 yards, and a mean dispersion in direction of 12.3 yards), and by the rapid firings (rounds 264 to 273 at 7100 yards having given a mean dispersion in direction of only 4 yards).
REMARKS REGARDING THE EXTRACTS FROM FIRING SHEETS AND THE DIAGRAMS OF POINTS OF FALL OF 8.27-INCH GUN No. 2.
Until shot No. 266, the charges were for the most part chosen to give an initial velocity averaging about 2903 f. s. and reaching as high as 3018 f. s. The increase of length of the powder space is consequently greater than in gun No. 1. The last 78 shots thus far fired, that is Nos. 267 to 344, were against armor plate, with charges and velocities reduced to give the desired velocity on impact.
On account of the constantly varying conditions of charges and projectiles, the initial velocities constitute, as a means of judging the durability of the guns, a less sure basis than in the case of gun No. 1; but very favorable testimony in this regard is given by the diagrams of points of fall contained in Appendix 2. On account of the less number of rounds, only two series of rounds at two different distances are here compared; besides this, the result of the last grand series of rounds is shown with the diagram of points of fall prior to the firing against armor plates (shots 234 to 247 at about 12,250 yards, having likewise given a very satisfactory accuracy). In a series of rounds fired still later (258 to 266 at about 8750 yards), the ranges were only estimated, on account of the marshy ground at the points of fall; the total dispersion in range was only about 164 yards.
Subsequent to the foregoing the endurance test of 8.2-inch gun No. 2 was continued up to a total number of more than 500 rounds. The mean initial velocity obtained during this continuation of firing was 2952 f. s., the weight of projectile being always 238 pounds. The firing was almost exclusively for accuracy at a distance of about 8750 yards, and the results exceeded every expectation. The dispersions remained in an absolutely uniform manner of the same value as in the first part of the trials. Thus there was obtained:2
Rounds 392 to 402 at 8,573 yards;
L50 = 32.7 B50 = 6.9 yards.
Rounds 409 to 412 at 8,443 yards;
L50 = 54.5 B50 = 5.1 yards.
Rounds 453 to 462 at 8,520 yards;
L50= 44.7 B50= 5.6 yards.
Rounds 463 to 472 at 8,390 yards;
L50 = 70.2 B50 = 4.6 yards.
Rounds 483 to 492 at 8,257 yards;
L50 = 39.6 B50= 7.5 yards.
Rounds 495 to 508 at 8,477 yards;
L50 = 33.1 B50 = 5.0 yards.
A comparison of the dispersion of the previous rounds, 212 to 227, with that of rounds 495 to 508, is especially instructive. The two diagrams are the results of firing with the same charge (82 rounds) and the same kind of powder; the temperature of the powder in the second case was 6° C. lower than in the first. Although about 300 rounds had in the meantime been fired, the rectangle of dispersion of the last series is only a little greater than that of the earlier one (166 against 153 square yards). To obtain the same range, it was necessary to increase the elevation about 1° in the last series.
THE KRUPP 11.02" GUN, LENGTH 45 CALIBERS.
(Light gun, Model 1901, with jacket and two rows of rings.)
Length of gun 501.4”
Length of bore 472.68”
Length of power space 90.85”
Length of rifled bore 381.83”
No. of grooves 80
Rifling 1 in 45, to 1 in 30 calibers.
Weight of gun, with breech closure 82,914 pounds
Weight of projectile 672 pounds
Initial velocity 2,821 f.s.
Muzzle energy 37,113 f.t.
2See the diagrams of points of fall in Appendix 2. L50 and B50 are the length and width of the rectangle containing 50 per cent of the impacts. Half the sides of this rectangle are the "probable errors" in range and laterally. The "mean error," or "mean deviation" is the probable error divided by .845.
REMARKS RELATIVE TO THE EXTRACTS FROM THE FIRING SHEETS AND THE DIAGRAMS OF POINTS OF FALL.
Up to the end of 1907 there had been fired, with a mean initial velocity of 2821 f. s., 138 rounds, of which 28, towards the end of the trials thus far carried out, had a mean initial velocity as high as 2886 f. s. Besides these 138 rounds there were 33 fired with initial velocity of 2690 f. s., and 21 with a velocity below 2624 f. s. The firings until then carried out with this gun had for an object, in the first place, experiments with powders; the determination of the life of the gun was only a secondary consideration. Not only were the weights of charge and the temperature of the powder very different, but the powders used were also of very varying dimensions and compositions. In about half, the tubular powder contained 15 per cent of nitroglycerine and in the other half 25 per cent. For these reasons the initial velocities given in the extracts from the firing sheets do not offer direct evidence bearing upon the question of the durability of the gun; but we may conclude that it has a very great longevity, in view of the excellent conservation of the accuracy of fire, especially as regards the dispersion in range, as may be seen from the diagrams of points of fall in Appendix 2. The increase of only about 1/3 of a caliber in the length of the powder space for 192 rounds speaks equally in favor of the gun's endurance.
ENDURANCE TESTS OF KRUPP NAVAL GUNS OF 8.27-INCH
AND 11.02-INCH CALIBER.
(L/45 Mod. 1901) AT MEPPEN.
(Extracts from the firing sheets.)
POINTS OF FALL.
RANGES AND SIDES OF 50% RECTANGLE IN YARDS.