Building the CASAS Model

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Building The CASAS Model

The CASAS analysis uses a finite element (Lumped Parameter) model to represent the chamber, breech bolt and cartridge case. The model is divided into four zones as shown below.

Zone 1 includes:

Spring To Ground - This spring ties the model to ground and is typically set to be 10 times the breech stiffness. The load on this spring is the load that must be reacted by the weapon's breech lock.
Breech Block - The mass of the breech block will be required.
Case/Breech Block Gap Spring - Represents the breech stiffness which should be measured on the weapon of interest or determined by analysis. This spring also includes a gap to represent the head space (axial gap between case base and bolt face). These parameters are extremely important to the quality of results from the analysis.
Case Base - The thick-walled section of the case is modeled as a single lumped mass and a spring. The user must determine the axial position of the transition between the case base and Zone 2 in the model. The case base section is assumed to be the portion of the case that does not contact the chamber during firing.

Zone 2 is the thin-walled body of the case. You will use the CASAS model generator to develop a lumped parameter model of Zones 2-4.

Zone 3 is the taper of the case. There are springs to ground that represent the axial stiffness of the chamber in this region. These stiffnesses are typically set to equal the spring to ground in Zone 1.

Zone 4 is the neck of the case. The bullet pull force is applied to the nodes in this region.

Ring Elements are used to model the thin wall sections (Zones 2-4) of the cartridge case. These elements are subject to both radial and axial loads as shown in the free body diagram below.