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Airgun Ammunition Project
Team Members
Bryan LaMora
Joe Ouellette
Zach Rohlfs
Team 07F
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Task: Provide an economical material to replace the current lead pellet.
Reason: Due to health concerns lead pellets will
eventually be discontinued.
Project Definition
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Specifications
Pellet Size:
-.177 cal.
-.176 +.003/-.0005
-.4 to 10.5 grain
-.195” to .260” (ASTM F 590)
-Any Shape
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Specifications
Requirements:
-minimum 24 lb shot force
-Non-Toxic
-100 ft/s to 1200 ft/s velocity range
--30 to 100 deg F operating temp.
-Immune to black oxide oils
-Remain intact after impact
-$.10 to $.80 per 100 pellet cost
-.835” @ 25yd Shot Group
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Ideas & Evaluation
- All steel pellet
- Composite pellet
- BB encased in plastic
- Steel cylinder encased in plastic
- Plastic and Iron filings mix
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Design Obstacles
-Metal and plastic composite
-Steel core
-Plastic exterior
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Design Obstacles
•Sacrificed aerodynamics to increase weight
•Keeping the manufacturing process as simple as possible
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Plastics Research
Requirements:
-Dense
-Impact resistant
-Fairly high melting point
-Inexpensive
-Easily molded or thermoformed
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Plastic Body Material
- Criteria- Impact resistant at
low temperature- High density- Low cost- Easily injection
molded
- Material- Polypropylene- Polystyrene- PVC- ABS- Acrylic- Polyester- Nylon- Polyethylene- Fluoropolymers- Polycarbonate
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Inner Material
- Criteria- Coefficient of
restitution- Density- Cost
- Materials- Aluminum - Nickel - Tin- Steel- Brass- Copper
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Bounce Back Effect
- Lead: 55 Feet- Copper: 77 Feet- Brass: 105 Feet- Steel: 314 Feet
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Bounce Back Results
Worst Case scenario coefficient of restitution: .22
Coefficient of restitution from tested : .106
Coefficient of restitution of lead: .16
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Pellet Flight Characteristics
Will the velocities be approximately equal?
Is the Cd, coefficient of drag constant?
How do we determine the coefficient of drag?
What does this all mean?
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Calculating Drag
AV
FC dd
2
21
Cd is the coefficient of
drag Fd is the force of drag is the density of the
fluid A is the cross-
sectional area. m is the mass of the
pellet ad is the acceleration
of drag V is the velocity of the
pellet at a given time, t
dd amF
dt
dVad
dx
dvVad
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Fluent and approximations
Experimental data is not needed.
Small geometries need to be scaled by Reynolds numbers.
Two dimensional approximations differ from three dimensional.
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Results and Their meaning
Cd~0.4 for hand calculations on the old pellet.
Cd~0.47 for the old pellet by Fluent using a two dimensional model.
Cd~0.56 for the new pellet by Fluent using a two dimensional model.
The velocity of the new pellet will degrade faster.
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A) Pressure is constant through barrel.
B) Temperature decrease due to pressure change of gas is neglected.
C) Temperature is constant.
D) Force of gravity is negligible on pellet.
Calculation Assumptions
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Pellet and Barrel
19.5”
.177”24 psi
Flow
Barrel: Brass 330
Rifling: 1 Twist in 14” Right Hand Lead
6 Lands .045” wide
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Force due to Pressure
AC = Contact Area
CL = Contact Length
w = Width of Contact Area
FP = Force due to Pressure
P = Air Pressure in chamber
2.00553inC
A
)02(.277. ininCA
WLCCA
.277inLC
)6(045. inLC
.133lbPF
)200553(.2
24 ininlb
PF
CPAPF
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Heat Generated by Friction
.0531lbf
F
)133)(.4(. lbfF
PFkfF
LB = Barrel Length
Wf = Work Due to Friction
FP = Force due to Pressure
DH = Change in Heat
lb.0863ftf
W
)121)(5.19)(0531(.inftinlb
fW
BLfF
fW
lb.0863ftΔΗ
f
W
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Temperature Change
)( PCMwt = Material Weight
DH = Change in Heat
CP = Heat Capacity
DT = Change of Temp
Pellet Weight
Lead = .512g
Plastic = .0418g
Barrel weight
Brass 330 = 185.07g
TLead Pellet = 1.77 C
TPlastic Pellet = 1.49 C
TBarrel = .0017 C
)(
))((
wtMPC
wtMPC
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Wk Mon Tues Wed Thur FriMarch1 10-14 First Day Back
2 17-21 Quarter Time Line update Empire update
3 24-28April 4 31-04 <-------------------------Tooling Setup---------------------------> Crosman Update Meeting
5 07-11 <---------------------------------------------Machining of f irst 7 pellets-------------------------------------------------------><--------Testing #1--------->6 14-18 <---------------------------------------------Machining of 40 new prototypes------------------------------------------------>
7 21-25 <--------Testing #2--------->May 8 28-02 <----------------------------------Technical paper edit------------------------------------------>Tech paper to Advisor for review .
9 05-09 <-----------Technical paper f inal edit--------------> Technical paper Turn in. Set up test f iring Pellet Firing Demonstration
10 12-16 <------------------------------Creation: poster/presentation-----------------------------> Deliverables w rap up Final Presentation
Prototyping & Testing Schedule
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Conclusions
The new Pellet met the following criteria: Functions in a .177 cal Air Rifle. Between 4 and 10 grains in weight. .255 in length Operates in a velocity range of 100 to 1200
ft/sec. Nontoxic and resistant to black oxide. Low Bounce back.
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Conclusions
The new Pellet fell short in the following areas: Utilize rifling in barrel:
Plastic did not conform to the rifling of the barrel.Under-sizing of pellet “skirt” will help pellet follow
rifling.
Accuracy:The lack of spin of the pellet out of the barrel.
Intact after impact:Prototype was hand machined, plastic did not “lock”
core into pellet.
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Questions?