20226-Improving Bullet Pull
Mark Lee, Dan Meierhofer, Eric Bultman – Orbital ATK
Nick Tashjian – ARDEC
22 Finite Element Analysis (FEA) Simulations were used to develop a
hypothesis for the cause of lower than allowable Bullet Pull forces
Seated Bullet
1 Bullet Insert
2-4 Bullet Seat
A single Bullet Insert simulation provides the initial state for 3 levels
of “overlap” (case overhanging cannelure) in Bullet Seating.
Case/bullet material models match the anneal and/or cold work
state of the manufactured components
Each of the 3 levels of Bullet Seating are
initial states for an additional 3 levels of Case Crimping that
produce the 3 levels of “engagement” (case material crimped
inside cannelure) for subsequent Bullet Pull. Color contours
indicate accumulating plastic strain in the case as the bullet is
inserted, seated, crimped, and pulled.
Small Overlap,
Light Crimp
Medium Overlap,
Medium Crimp
Large Overlap,
Heavy Crimp
Engagement
Overlap
• Established the physics of the root cause of low Bullet Pull
• Instructed the use of physical measurements from troubled cartridge lots
• Guided the setup of physical experimentation to prove root cause
• Bullet Pull increases with Engagement—change process to increase minimum engagement via
crimp displacement and force procedures; restrict maximum cannelure diameter
• Long Overlap with insufficient crimp has the lowest Bullet Pull—establish upper limit on
Overlap via component/assembly tolerance changes
5-13 Crimped Case
Extracted Bullet
14 – 22 Bullet Pull Force
350
400
450
500
550
600
3.25E-03 3.75E-03 4.25E-03 4.75E-03 5.25E-03 5.75E-03 6.25E-03 6.75E-03 7.25E-03 7.75E-03
Bullet Pull Force
Engagement
Large
Medium
Small
Medium, Extra Crimp
Overlap
FEA Results
23
DISTRIBUTION A: APPROVED FOR PUBLIC RELEASE - DISTRIBUTION UNLIMITED
FEA Conclusions
Unclassified
