Me 109 30mm weapon

[funked]

Toad it's the other way around.  Imagine two projectiles of precisely the same shape and size, fired with the same muzzle velocity.  The heavier one will drop less at a given distance downrange.

Think superball vs. ping pong ball.  

[This message has been edited by funked (edited 04-03-2000).]

[Toad]

I am in fact wrong.

That will teach me to post on this subject without reviewing my ballistic data!    

Using the Speer Reloading Manual Number 10 as a reference, ballistic coeficient is the key.

"Ballistic Coefficient: Ratio of the sectional density of a bullet to its coefficient of form. Represents the projectile's ability to overcome the resistance of the air in flight."

It's not the size, weight or the sectional density of the bullet alone that makes the difference, it's the resulting BC.

Now, for an example:

The Speer .284-145 grain (7000 grains/pound) SP bullet and the .338-275 grain SS bullet both have a Ballistic Coefficient of .46.

Start both of them at the same muzzle velocity and the exterior ballistics are identical, because the BC is identical.

For example, with a 200 yard "0" and a muzzle velocity of 3000 FPS, both bullets "fly" the same trajectory.

They will be 1.3" above the Line of Sight at 100 yards, "on" at 200, drop 6.7" below LOS at 300 yards, -19.4" at 400 and -39.2" below LOS at 500 yards.

This is despite the potentially confusing fact that one bullet is almost twice as heavy and about 20% larger in diameter than the other. They still fly the same trajectory.

Muzzle velocity and "zero" are the variables that determine drop given a known BC.

I'd bet that the 20MM Hispano and the 30MM 108 don't have the same BC, however.

If you increase BC, you get a flatter trajectory. For example, the best BC in the book is a .284-165gr BT bullet.

At a MV of 3000 and a 200 yard zero it does significantly better than the .284-145gr (BC .46.) It drops almost a 1/2" less at 300, an inch less at 400 and about  3" less at 500 yards.

Energy, measured in Foot Pounds per Grain, is independent of BC. Any bullet moving at 3000 FPS MV has the same Muzzle Energy in Foot Pounds/Grain (19.98) no matter what the BC. (Decreasing, of course, as velocity decreases.) So here the heavier bullet would have an advantage; more grains, more foot pounds.

I wonder what the BC of a superball and a ping pong ball are?    

This may be MORE than we really wanted to know?    

Sorry guys, should have reviewed my book before I stuck my hoof in my mouth. Been longer than I thought since I did any serious reloading.

[This message has been edited by Toad (edited 04-04-2000).]

[This message has been edited by Toad (edited 04-04-2000).]

[funked]

Good job!  You da man!

I only knew that because my first class in numerical methods (aka computer simulation) centered around simulating artillery projectiles.  It was a convenient example I guess.

Never took a class where we figured out what happens when the projectile hits something though.    

[This message has been edited by funked (edited 04-04-2000).]

[skippy]

thats a 30mm cannon?  thought it was a mortar.....  if we can play the "this gun , no that gun thingy" how about 6 x 13mm on the 109 ! thats what i want.

[This message has been edited by skippy (edited 04-16-2000).]

[Fishu]

I Would personally prefer MG151/20 over MK103 and MK108 anyday  

1. If I am going for fighter hunt, I feel much more comfortable with higher velocity cannon.

2. One miss not so bad with 20mm  

3. What 20mm takes as more hits, 30mm loses with shorthage of ammunition and velocity (serious drawback for hitting!)

4. 10-15 rounds of MG151/20 has been enough for me to bring down any fighter.  
..so far