I have been moulding my own rounds using a lead nose and polyurethane.
I would like to hear anyones suggestions as to the best shape for accuracy.
The size of the rounds vary from 12.7mm to 18mm and are usually 15 to 25 mm long respectively. Cheers.
Peace
Scotty
Ammo
-
jackssmirkingrevenge
- Five Star General
- Posts: 26204
- Joined: Thu Mar 15, 2007 11:28 pm
- Has thanked: 572 times
- Been thanked: 345 times
since you're not spinning your rounds, you need them to be drag stabilised, either using fins or, easier option, with a hollow tail. What calibre is your launcher? For a 3/4" caliber I found that (aside from spherical projectiles) these were the best option: slugs for a 3/4" barrel - takes a bit of work to make one but they're fairly sturdy and usually re-usable, depends what you're shooting at.
hectmarr wrote:You have to make many weapons, because this field is long and short life
-
jimmy101
- Sergeant Major
- Posts: 3199
- Joined: Wed Mar 28, 2007 9:48 am
- Location: Greenwood, Indiana
- Has thanked: 5 times
- Been thanked: 17 times
- Contact:
Like JSR said, hollow tail.
A solid but light tail is the same as a hollow tail, as long as the density of the tail is much less than the density of the nose.
A lead nose with a piece of polyurethane foam rod of the same diameter should be stable. Figure the length of the low density rod as about 3x the length of the lead nose. Wood is enough lighter than lead that it would probably work as well. (The basic aerodynamics of a bottle rocket.)
Easy enough to figure out if a simple bullet shape will be aerodynamically stable or not. Put one together and find the front to back balance point. (This is the front to back center of mass of the projectile). Trace the outline on a piece of cardboard and cut it out. Find the front to back balance point of the piece of cardboard. (This is the approximate center of drag/pressure/thrust of the projectile.)
For the round to be stable the balance point of the actual round should be ahead of the balance point of the piece of cardboard by at least the diameter of the round. (Or is it at least 2x the diameter of the round?)
A solid but light tail is the same as a hollow tail, as long as the density of the tail is much less than the density of the nose.
A lead nose with a piece of polyurethane foam rod of the same diameter should be stable. Figure the length of the low density rod as about 3x the length of the lead nose. Wood is enough lighter than lead that it would probably work as well. (The basic aerodynamics of a bottle rocket.)
Easy enough to figure out if a simple bullet shape will be aerodynamically stable or not. Put one together and find the front to back balance point. (This is the front to back center of mass of the projectile). Trace the outline on a piece of cardboard and cut it out. Find the front to back balance point of the piece of cardboard. (This is the approximate center of drag/pressure/thrust of the projectile.)
For the round to be stable the balance point of the actual round should be ahead of the balance point of the piece of cardboard by at least the diameter of the round. (Or is it at least 2x the diameter of the round?)
Jimmy that what i thought too kinda- however the hollow tail would improve muzzle velocity due to the lighter weight round, thanks for that idea Jack (i actually had the same thought today, about making a top plate with pegs that are aligned with the centre of the round, i make like 15-20 at a time, jus wasn't sure how that idea would "fly")
Off topic banter- I have a S/S Hybrid that's about 600ml ( it takes 22cc Butane for normal combustion, someone can figure out how big it is for me
3.12% Butane is optimal!) Anyhoo it had a leak, i fixed, Loaded polynut round, injected 44cc Butane, Put 15psi into her ( i know that means she is running a bit rich maybe) Aimed at 5 gallon metal drum approx 4-5 Metres away, Clicked igniter, Witnessed instant holes in both sides of drum... It didn't slow down... Hit tarp 20 metres behind target a near flat trajectory, Hit and went through 1/2 inch thick plywood box that our panel saw is stored in, Thats it, i have to open the box tommorrow and see what damage it did to the saw!....
Peace
Scotty
Off topic banter- I have a S/S Hybrid that's about 600ml ( it takes 22cc Butane for normal combustion, someone can figure out how big it is for me
3.12% Butane is optimal!) Anyhoo it had a leak, i fixed, Loaded polynut round, injected 44cc Butane, Put 15psi into her ( i know that means she is running a bit rich maybe) Aimed at 5 gallon metal drum approx 4-5 Metres away, Clicked igniter, Witnessed instant holes in both sides of drum... It didn't slow down... Hit tarp 20 metres behind target a near flat trajectory, Hit and went through 1/2 inch thick plywood box that our panel saw is stored in, Thats it, i have to open the box tommorrow and see what damage it did to the saw!....Peace
Scotty
-
jackssmirkingrevenge
- Five Star General
- Posts: 26204
- Joined: Thu Mar 15, 2007 11:28 pm
- Has thanked: 572 times
- Been thanked: 345 times
think shotgun slugs:
The "air rifling" doesn't have any appreciable effect, what keeps the slug stable when fired from a smoothbore barrel is the lightweight plastic or fibre tail attached to the base.
One advantage of using a hollow tail is that the propellant gasses tend to "inflate" it, sealing it against the barrel and preventing any blowby.
The "air rifling" doesn't have any appreciable effect, what keeps the slug stable when fired from a smoothbore barrel is the lightweight plastic or fibre tail attached to the base.
One advantage of using a hollow tail is that the propellant gasses tend to "inflate" it, sealing it against the barrel and preventing any blowby.
hectmarr wrote:You have to make many weapons, because this field is long and short life
-
jackssmirkingrevenge
- Five Star General
- Posts: 26204
- Joined: Thu Mar 15, 2007 11:28 pm
- Has thanked: 572 times
- Been thanked: 345 times
woof! 
lol
lol
hectmarr wrote:You have to make many weapons, because this field is long and short life