Benefits of Two Dimensional Internal Ballistics Modelling for Small
Calibre Cased Telescoped Ammunition
I. Robertson
1
, M. Pocock
1
, C. Woodley
2
, S. Georgi
1
, R. Threlfall
3
, C. Guyott
1
1
Frazer-Nash Consultancy, Stonebridge House, Dorking Business Park,
Dorking, Surrey, RH4 1HJ, UK, email: i.robertson@fnc.co.uk
2
QinetiQ, Fort Halstead, Sevenoaks, Kent, UK
3
Oxford University, Engineering Dept, Oxford, UK
Session: Interior Ballistics
Presentation preference: Oral
Introduction
Currently there is a drive to reduce the burden on the dismounted soldier in order to
increase his or her agility and endurance, thus reducing casualties and injuries. One
of the largest contributors to the total weight burden on the dismounted soldier are
ammunition and weaponry. The Lightweight Small Arms Technologies (LSAT)
programme has been established in the US to concurrently develop lightweight
weaponry and two types of ammunition technology to replace the conventional
5.56 mm NATO round currently in service (Reference 1). The presently favoured
munition is the Cased Telescoped (CT) round which has been developed to
operational prototype stage.
The commercially available one-dimensional, internal ballistics code, FNGUN, has
been used during the LSAT program to inform the ammunition designers and cut the
cost of expensive firing tests. FNGUN2D, a two-dimensional version of FNGUN, has
recently been released and therefore was not available for the LSAT modelling. This
two-dimensional code incorporates the well respected QIMIBS solver developed by
QinetiQ Ltd (Reference 2) and offers much greater fidelity when modelling complex
gun systems (References 2, 3 and 4).
FNGUN2D is used in this paper to simulate the operation of a weapon firing a
generic 7.62 mm CT round, to investigate if similar weight savings to the 5.56 mm CT
round can be achieved whilst maintaining performance conditions such as muzzle
velocity and peak pressure. The paper highlights the benefits of a two-dimensional
internal ballistics code over a one-dimensional code for this application. The study
solely uses open literature data relating to the small calibre rounds for the purposes
of a publishable paper.
Modelling of a conventional 7.62 mm round is undertaken in order to derive the
propellant properties, by tuning these properties to the openly available operating
conditions namely maximum pressure and muzzle velocity (Reference 5). These
propellant properties will be used when simulating the CT round using FNGUN2D.
The conventional round is modelled in FNGUN and FNGUN2D to highlight how the
internal ballistics can be modelled in one dimension with a good level of accuracy
and to gain confidence in the FNGUN2D predictions of small calibre weapons.
The LSAT program achieved approximately 40% weight reduction in the mass of a
linked ammunition round through the use of polymer casing, plastic links and
compacted propellant without any loss in performance conditions (Reference 1). This
paper describes the possible weight saving for a 7.62 mm CT round based on a
scaling of the 5.62 mm CT round and does not include any weight saving provided by
a compacted propellant. A schematic of the proposed 7.62 mm CT round is shown in
Figure 1.
