IMPROVED AUTOMATIO ČAS CHECKS FOR PROJECTILES
Year: 1878

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LETTERS PATENT to Thomas James Smith, of the Firm of Robertson, Brooman,
and Company, of 166, Fleet Street, in the City of London, Patent Agents, for
the Invention of IMPROVED AUTOMATIO ČAS CHECKS FOR PROJECTILES"
A communication from abroad by John Gazzam Butler, Captain of Ordnance,
West Troy, New York, United States of America.
caled the 24th December 1878, and dated the 24th June 1878.
COMPLETE SPECIFICATION filed by the said Thomas James Smith at the
Office of the Commissioners of Patents on the 24th June 1878.
THOMAS JAMES SMITH, of the Firm of Robertson, Brooman, and Company, of
166, Fleet Street, in the City of London, Patent Agents. "IMPROVED AUTOMATIC
GAS CHECKS FOR PROJECTILES." A communication from abroad by John Gazzam
Butler, Captain of Ordnance, West Troy, New York, United States of America.
This Invention relates to certain devices called "gas checks" or sabots, the
object of which is to close the windage of projectiles, thus preventing the wasteful
and destructive action of the powder gases, more especially in rifled guns'; and they
may be attached to the projectile permanently, at the works, or just previous to
loading, or they may be loaded separately from the projectile.
A gas check which affords the option of loading with the projectile, or indepen-
dently of it may be called "automatic," and the present Invention relates princi-
pally to this class, having reference to a gas check which shall not only close
windage, but shall also be capable of rotating the projectile, that is, of conveying
to it the full rotation due to the "pitch" of the rifling.
With a view to a clearer understanding of the precise nature of these improve-
ments, I will refer to Figures 1, 2, 3, 4, 5, and 6, on Sheet I., designs which are so
accurately described in previous Letters Patent granted to my foreign correspondent,
No. 1510", that I cannot do better than quote from said Letters Patent in this
place. Referring to these Figures,
A indicates the body of the projectile, and B, my double lipped band applied
"thereto; x x x x x E is the annular slit groove or channel between the two

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lips of the band, and may be cast or cut in as may be preferred; × × × × × O is
"the upper lip, and P the lower lip of the annular band; E is the opening
"between the lips, designed to receive the powder gas, which is instantly and
evenly distributed around said opening or annular groove; S, T, is a beviled
junction, straight or curved, of the band and projectile.
"
"
"
The material of the double lipped band may be any ductile and tough metal,
" but in practice a proportion of copper 25 and tin 1 has been found to give
"excellent results.
5
The practical operation of this projectile is as follows:-The projectile being
"londed without respect to the grooving of the gun, and the gun discharged, the 1
"powder gas is quickly and evenly distributed around the annular channel E, and
"the upper lip O is evenly and uniformly expanded into the grooves of the gun,
whereby the desired rotation is communicated to the projectile. While however
"the upper lip is freely expanded into the rifling of the gun, and performs its duty
" of coinmunicating the twist of said rifling to the projectile, the lower lip P is 1
pressed upon the body of the projectile, with an intensity proportionate to the
"force of discharge, and thus stripping is rendered impossible, except through
gross defects of material or workmanship. The beveled surface S, T, is an
additional precaution against the breaking of the projectile, the lower lip P
serving as a 'gas check,' being a chief preventive in this respect, as has been s
explained. Suppose the upper lip to be distended by the discharge, the material
of the band folds or upsets to some extent upon itself, and what pressure obtains
upon S, T, being normal to it, it is better able to withstand without giving way.
Moreover, the angle at S is very strong, and in pressures of great violence the
" softer metal of the band would ride up on the beveled surface S, T, rather than 2
break the projectile.
"
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E
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"Although it is preferred to use the screw thread (as a incans of attachment),
particularly in projectiles of large calibre, yet it is probable that the downward
pressure of the gases upon the lower or inner flange will be sufficient to sink it
into any irregularities of surface provided for the purpose upon the base of the
projectile, in place of the screw. In such case, the sabot could be slightly forced
upon the projectile in its manufacture, and the bite would be secured by
means of
gas pressure upon the flange P to retain the sabot in position upon the
projectile during its passage through the gun, and during flight."
"The side slip (independent rotation) of the gas check being prevented by the
"notched base or conc S, T, already described.
"
"Various other forms of sabots (gas checks) are shown, all of which however
"embrace the fundamental principle of combining with the wedging portion of thic
sabot, a lower flange or lip (and most generally also an upper or outer lip) which
shall operate as a gas check in excluding the gas from its interior, and which also
by its extent of surface, is capable of a more secure attachment to the projectile,
"which attachment is likely by gas pressure to be more firm after firing than
" before it."
Thus were described gas checks which have been proved of unqualified excellence,
but which it was intended should be permanently attached to the projectile in
manufacture, or at least slipped on to the projectile before loading. But fears have
been expressed that gas checks, if permanently attached to the projectile, would be
very liable to injury in handling and transportation, and hence it has been thought
desirable to provide if possible (at least until the question is settled), a means of
attaching these gas checks, not only immediately previous to loading, but if possible
to provide that they may be loaded separately from the projectile when desired.
Especially in this latter case, it was feared that the gases of discharge would find
entrance under the lower lip or flange P, before it could become accurately ad-
justed to its place, and to guard against such a contingency the expedient has been
resorted to of extending the lower lip P over the entire base of the projectile, or
connecting its rim by a disc p, which however superfluous in permanently attached
gas checks, may prove an improvement of merit where the gas check is required to.

page_text: play a game of leap-frog with the projectile. If therefore this connection of the
lower lip of my gas check by a thin disc extending over the base of the projectile,
constitutes a patentable feature or improvement, I do not claim it.
The placing of exterior projections S, S, upon the gas check to fit into the
corresponding grooves of the rifling is attended with more or less trouble and
expense, they cause additional friction and delay in loading, and serve no useful
purpose except to stop the projectile at the bottom of the rifling, and thus leaving
the desired air space between the cartridge and the projectile in the purely hypo-
thetical case of an invariable charge and longth of chamber. If however these
projections are provided, then it is clear that very much less expansibility of the
gas check is required (since the grooves of the rifling being already filled, only
windage has to be closed) and we may therefore either greatly diminish the expan-
sible portion of the gas check, the upper lip or flange o, or change the design, and
dispense with it altogether.
These considerations lead us to Figures 7 and 8, forms of automatic gas checks
which may be found to answer well the purpose intended. They consist of simple
cup-shaped devices with the usual projections on the exterior, and beveled on the
interior to fit over the correspondingly tapered base of the projectile.
These gas checks may be either slipped on to the projectile just before loading, or
they may be inserted on top of the cartridge, or independently, and after being
ramined home, the projectile is inserted and set into the gas check which either
rests against the top of the cartridge, or the bottom of the rifling. Upon discharging
the gun, the gas check is driven upon the conical base of the projectile, the angle of
which is just sufficient to allow the part B of the gas check to be expanded or
wedged out to fill windage tightly, with sufficient surplus, "drive," or motion, to
compress upon and secure a "bito" into the ridges and depressions and d on the
projectile, whereby it not only grips the latter sufficiently to rotate it, but is held
in place during flight. The inner conical surface of the cup may be ridged if
desired to correspond to corresponding elevations and depressions on the conical
base of the projectile.
Gas checks of this form, Figures 7 and 8, will be open to the objection of receiving
their maximum distension at the point of maximum pressure near the seat of the
charge, and will consequently by attrition become somewhat looser as they near
the muzzle.
Whereas, if there is provided a feature capable of even moderate expansion, such
as an outer lip or projecting flange; this will be kept distended during the passage
of the projectile through the bore. This form is shown in Figure 11, where o is
the expansible part referred to, and if the wedging part be shortened, as shown at
bin dotted lines, the gas check will be reversible, and may be loaded either face
next the projectile. We have thus an expanding cup, the only novelty of which
consists in its being made automatic by combining it with a wedging part b.
Referring to Figures 9 and 10, we obtain expansibility to any desired extent by
the groove E, and this leaves Figure 9 to differ from Figure 6 mainly in method of
attachment. In Figure 6, the gas check becomes fast to the projectile by the
pressure of the lower flange P into the grooved by the gases of discharge, while in
Figure 9, the wedging part of the gas check is crowded by pressure against the
walls of the gun into the depression d, and wedging is a main feature, and ex-
pansion simply auxiliary.
In Figure 10, the lower lip or flange is curled around the base of the projectile,
instead of extending entirely across.
Figure 12 represents a gas check which may be applied just previous to loading,
and in which a close fit of the lower flange P is secured upon the tapered base by
means of a rubber band shown at R in cross section, which is let into a circular
recess for the purpose, and projecting slightly beyond the inner surface of the
flange, is capable of slight compression, as the gas check is slipped on to the pro-
jectile and pressed forward before loading. x is an inner circular groove to facilitate
the spreading of the part y of the gas check as it expands into the offset d, while

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the part is wedged and compressed between the walls of the gun, and the screw
ridges on the conical surface, thereby preventing detachment after firing, as well
as securing the rotation of the projectile by affording the necessary "grip."
Reference has already been made to the only argument for the presence of
exterior projections S on the gas check, namely, as a means of stopping the projectile
at the bottom of the rifling and short of the cartridge, that the desired air space
may be preserved between the cartridge and the base of the projectile. Figures 13
and 14 show a means of accomplishing the same end, while retaining all the merit
of a plain gas check firmly attached to the projectile, and of a shape which has
proved so perfect in practice. This improvement consists in drilling one or more
holes at proper points around the sabot or gas check, and immediately before
loading, or at any convenient time prior thereto, driving in little plugs or buttons
of suitable shape, such as are shown. These sliding in the grooves will of course
stop the projectile at the desired point, and to make allowance for a varying charge
there may be other holes provided in the body of the projectile, as at h'. In Figure
12, another form is shown, a "clip" being hung on to the lip of the gas check prior
to loading.
As a means of preventing the bruising or denting of the outer lip or flange of the
gas check, the groove or gas channel E may be filled with any hard substance, as at
Fin Figure 13 or 14. This substance may be a hard metal cast into the groove.
In Figure 14, it serves the additional purpose of holding the gas check in place.
Having thus described the nature of the said Invention and in what manner the
same is to be performed, I declare that I claim,-
Firstly. The cup-shaped gas checks B, shown in Figures 7 and 8, in combination
with a projectile having a truncated and serrated base for automatic attachment,
effected by the discharge, as herein-before described.
Secondly. The combination of the gas checks shown in Figures 9 and 10, with
the notched or grooved basc, as set forth.
Thirdly. The cup-shaped gas check shown in Figure 11, capable of being made
reversible, if constructed according to the dotted line b.
Fourthly. The rubber packing ring R seen in Figure 12, when used for the
purpose set forth.
.
Fifthly. The circular inner groove a, Figure 12, acting as und for the purpose
hercin-before described.
Sixthly. The plugs, stops, buttons, or studs 7, Figures 12, 13, and 14, acting as
and for the purposes set forth.
Seventhly. The hard filling F under the upper flange of the gas checks shown in
Figures 13 and 14, as herein-before described, and for the purposes set forth.
In witness whereof, I, the said Thomas James Smith, have hereunto set my
hand and seal, this Twenty-fourth day of June, One thousand eight hundred
and seventy-eight.
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ATHET