Team 07 F Airgun Ammunition Project Team Members
Team 07 F Airgun Ammunition Project Team Members Bryan La. Mora Joe Ouellette Zach Rohlfs
Project Definition Task: Provide an economical material to replace the current lead pellet. Reason: Due to health concerns lead pellets will eventually be discontinued.
Specifications Pellet Size: -. 177 cal. -. 176 +. 003/-. 0005 -. 4 to 10. 5 grain -. 195” to. 260” (ASTM F 590) -Any Shape
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” @ 25 yd Shot Group
Ideas & Evaluation - All steel pellet - Composite pellet - BB encased in plastic - Steel cylinder encased in plastic - Plastic and Iron filings mix
Design Obstacles -Metal and plastic composite -Steel core -Plastic exterior
Design Obstacles • Sacrificed aerodynamics to increase weight • Keeping the manufacturing process as simple as possible
Plastics Research Requirements: -Dense -Impact resistant -Fairly high melting point -Inexpensive -Easily molded or thermoformed
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
Inner Material - Criteria - Coefficient of restitution - Density - Cost - Materials - Aluminum Nickel Tin Steel Brass Copper
Bounce Back Effect - Lead: Copper: Brass: Steel: 55 Feet 77 Feet 105 Feet 314 Feet
Bounce Back Results Worst Case scenario coefficient of restitution: . 22 Coefficient of restitution from tested : . 106 Coefficient of restitution of lead: . 16
Pellet Flight Characteristics z Will the velocities be approximately equal? z Is the Cd, coefficient of drag constant? z How do we determine the coefficient of drag? z What does this all mean?
Calculating Drag z Cd is the coefficient of drag z Fd is the force of drag z r is the density of the fluid z A is the cross-sectional area. z m is the mass of the pellet z ad is the acceleration of drag z V is the velocity of the pellet at a given time, t
Fluent and approximations z Experimental data is not needed. z Small geometries need to be scaled by Reynolds numbers. z Two dimensional approximations differ from three dimensional.
Results and Their meaning z Cd~0. 4 for hand calculations on the old pellet. z Cd~0. 47 for the old pellet by Fluent using a two dimensional model. z Cd~0. 56 for the new pellet by Fluent using a two dimensional model. z The velocity of the new pellet will degrade faster.
Calculation Assumptions 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.
Pellet and Barrel Flow . 177” 24 psi 19. 5” Barrel: Brass 330 Rifling: 1 Twist in 14” Right Hand Lead 6 Lands. 045” wide
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
Heat Generated by Friction LB = Barrel Length Wf = Work Due to Friction FP = Force due to Pressure DH = Change in Heat
Temperature Change Mwt = Material Weight DH = Change in Heat CP = Heat Capacity DT = Change of Temp Pellet Weight DTLead Pellet = 1. 77 °C Lead =. 512 g DTPlastic Pellet = 1. 49 °C Plastic =. 0418 g DTBarrel weight Brass 330 = 185. 07 g =. 0017 °C
Prototyping & Testing Schedule
Conclusions z The new Pellet met the following criteria: y. Functions in a. 177 cal Air Rifle. y. Between 4 and 10 grains in weight. y. 255 in length y. Operates in a velocity range of 100 to 1200 ft/sec. y. Nontoxic and resistant to black oxide. y. Low Bounce back.
Conclusions z The new Pellet fell short in the following areas: y. Utilize rifling in barrel: x. Plastic did not conform to the rifling of the barrel. x. Under-sizing of pellet “skirt” will help pellet follow rifling. y. Accuracy: x. The lack of spin of the pellet out of the barrel. y. Intact after impact: x. Prototype was hand machined, plastic did not “lock” core into pellet.
Questions?
- Slides: 25