the field artillery journal - Fort Sill - U.S. Army

SUPPLEMENTAL NOTES ON LOST MOTION
breech mechanism. They go to show, however, the presence of
lost motion in designs other than our own; they indicate that
lost motion does affect the accuracy with certain types of
carriages. In view of the marvelous results attributed to the
"Soixante quinze" in the present war where such enthusiastic
references include this Deport type, we may feel assured that
the design has been considerably improved in this respect or
that the gunners have learned how to control lost motion. 3
3
The following is taken from a memorandum on the subject of lost motion in the
Deport carriage, prepared at the Rock Island Arsenal, June 5, 1914.
"1. Before Road Test, measured May 4, 1914.
"In elevation, Gun at -7.5 degrees depression, lost motion was 13.9 mils
" " 0. " " " " 18.4 "
" " 15. " elevation " " " 18.0 "
" " 25. " " " " " 4.74 "
"2. After Road Test, measured June 3, 1914.
"In elevation, Gun at -7.5 degrees depression, lost motion was 18.95 "
" " 0. " " " " 23.7 "
" " 15. " elevation, " " " 23.1 "
" " 25. " " " " " 10.95 "
"3. Before and after Road Test, on dates above.
Mils before Mils after
"In traverse, Gun at zero azimuth ......................................... 10. 13.
Guns at 250 mils (pointing right) ..................... 10. 13.
" " 250 " ( " left)..................... 9. 11.
" " 400 " ( " " ) ..................... 6. 8.
" " 400 " ( " right)..................... 7. 10.
"4. From the above figures it is seen that the lost motion in elevation was increased
by 5 mils and in traverse by 3 mils, due to the road test, for practically all positions in
elevation and traverse.
"5. It should be noted that the construction of the Deport carriage is such as to
permit the gun to be thrown considerably off the target beyond the position where
all lost motion in the gears is taken up by force exerted at the breech in firing,
maneuvering, etc. The elevating cranks on the trails turn if the gun is jolted up and
down and the traversing handwheel runs around readily when force is exterted on
the breech in the direction of azimuth. After the road test, this derangement was
much more easily obtained especially in azimuth, by forcing the piece around with
one hand on the operating lever of the breech block through 250 mils or more. This
additional derangement does not occur in the service 3-inch field gun, as after the
lost motion is taken up the piece comes practically to a positive stop. Moreover, the
connection of the trail and axle of the Deport carriage is such that if the brake is
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