Influence of chamber misalignment on cased telescoped (CT)
ammunition accuracy
D. CORRIVEAU *, C. FLORIN PETRE
Defence R&D Canada, 2459 De La Bravoure Rd., Quebec, QC G3J 1X5, Canada
Received 19 September 2015; revised 12 November 2015; accepted 13 November 2015
Available online 17 December 2015
Abstract
As part of a research program, it was desired to better understand the impact of the rotating chamber alignment with the barrel throat on the
precision and accuracy of a novel cased telescoped (CT) ammunition firing rifle. In order to perform the study, a baseline CT ammunition chamber
which was concentric with a Mann barrel bore was manufactured. Additionally, six chambers were manufactured with an offset relative to the
barrel bore. These chambers were used to simulate a misaligned chamber relative to the bore axis. Precision and accuracy tests were then performed
at 200 m in an indoor range under controlled conditions. For this project, 5.56 mm CT ammunition was used. As the chamber axis offset relative
to the gun bore was increased, the mean point of impact was displaced away from the target center. The shift in the impact location is explained
by the presence of in-bore yaw which results in lateral throw-off and aerodynamic jump components. The linear theory of ballistics is used to
establish a relationship between the chamber misalignment and the resulting projectile mean point of impact for a rifle developed to fire CT
ammunition. This relationship allows for the prediction of the mean point of impact given a chamber misalignment.
Crown Copyright © 2016 Production and hosting by Elsevier B.V. on behalf of China Ordnance Society. All rights reserved.
Keywords: Cased; Telescoped; Ammunition; Aerodynamic; Jump; Accuracy
1. Introduction
The introduction of new electronic sights to increase
warfighters’ awareness and communication capability on the
battlefield has the potential to significantly increase their effec-
tiveness. However, these new pieces of equipment increase the
weight burden that must be carried by the soldiers. This, in turn,
reduces their mobility and agility.
Two areas where significant weight reduction could be
achieved are the weapon system and the ammunition. In order
to reduce the weight of the ammunition, several concepts are
being investigated and reached a high technology readiness
level. Among these, polymer cased ammunition, caseless
ammunition (CL) and cased telescoped ammunition (CT) are
the most promising. Using these technologies, ammo/link
weight reduction of the order of 37% and 12% volume reduc-
tion could eventually be achieved
[1].
For polymer cased ammunition, a standard rifle chamber can
be used. However, for CL and CT ammunition a rotating or
sliding cylindrical chamber must be used for both in-line, push
through feed and ejection. With such a mechanism, there exists
a possibility that the rotating or sliding chamber axis be slightly
misaligned with the barrel axis. If this occurs, as the projectile
is propelled out of the CT ammunition casing and it enters the
leade (freebore) area before the barrel engraving, the projectile
axis relative to the barrel axis will be at an angle. Therefore, the
projectile gets engraved in the rifling at an angle relative to the
barrel axis. This misalignment or tilt of the projectile has been
shown to result in a lateral throw-off at the muzzle and an
aerodynamic jump.
This is significant for high-precision gun designers as the
aerodynamic jump and lateral throw-off are a significant source
of dispersion. In the case of a CT ammunition rifle with a
misaligned chamber, it is believed that this would affect the
accuracy of the rifle in the form of a bias in the mean impact
point and to a lesser extent the precision. This is explained by
the fact that in the case of a misaligned chamber, the projectile
would generally be always tilted in the same direction as it gets
engraved after exiting the chamber.
In order to reduce the bias and the dispersion associated with
the aerodynamic jump and the lateral throw-off, the gun’s twist
rate can be reduced to lower the spin rate of the projectile at the
Peer review under responsibility of China Ordnance Society.
* Corresponding author. Tel.: +1 4188444000.
E-mail address:
daniel.corriveau@drdc-rddc.gc.ca (D. CORRIVEAU).
http://dx.doi.org/10.1016/j.dt.2015.11.008
2214-9147/Crown Copyright © 2016 Production and hosting by Elsevier B.V. on behalf of China Ordnance Society. All rights reserved.
Available online at www.sciencedirect.com
Defence Technology 12 (2016) 117–123
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