SpudFiles

I countersunk a dimple on the face of the cork and hot glued the marble into it.

These are rough prototypes before cleanup.

This design may offer 'cartridge' loading.

The natural cork round weighs 112 grains.

The artificial (rubber) cork round weighs 148 grains.

What do you think about its ballistic coefficient compared to a sphere?

Poor man's Brenneke slug

boyntonstu wrote: What do you think about its ballistic coefficient compared to a sphere?

It would be much better if the marble was recessed to it's half diameter point. Eliminate the flat surface of cork which defeats the purpose somewhat.

Even better, why not drive a short fat bolt into the cork?

Replace the cork by a small section of pipe and be done ..

I agree that putting the marble farther in so that the center of the marble is level with the front of the cork would reduce turbulence and thus drag in front. Also, the flat back of the cork will give you additional drag, you could file it down to a tapering curve for better performance.

On the other hand, being really careful kinda defeats the purpose of easy cheap ammo. Your choice.

I would put the marbles farther in if you wanna use corks. if it were me i would use pvc instead of corks because then you could sink the marble in to your desired spot and have a hollow back end for stabilization. For both ammos i would only expect exceptional accuracy to about 30 feet with a proper metal barrel.

Brian the brain wrote:Replace the cork by a small section of pipe and be done ..

Like this? Or, should I shorten it?



Note that the metal primer holder ring has been removed.

The plastic "pipe" that remains is a perfect fit for copper type L 3/4"!

I couldn't get the marble to where I wanted it, but you should get the idea.

BTW have you seen these shots with a flat front and rear projectiles?

Pretty darn good. 905 grains!

http://www.glbarnes.com/field_justice.html

Thats a good idea, to bad i don't have a shotgun.

Do these all weigh exactly the same...in grains?

I really dont see the appeal of using marbles inconsistant, light and expensive, as Jack suggested previously in this thread a bolt and nut would be a far better option. I posted chronograph results for shotshells at low pressure here http://www.spudfiles.com/forums/brass-h ... 20581.html , if you want a blunt projectile use a bolt in place of the nail. You already have a perfectly centred hole to use in the primer socket, so make use of it!

Using the primer hole up front, you add dead space inside the empty hull.

You push a marble into the hull and place hot glue on the crimp.

When you turn it over, the marble falls and it centers itself in the crimp and is glued in place.

Prochrono results today:

10d nail 184 gr 879 fps 600 psi
192 701
180 658
166 664
182 714

Marble 156 854
162 614
160 766

I believe that my manual operation of the 1/2' BV pilot is causing the inconsistencies.

The potential is there as seen in the higher numbers.

I need a spring and a trigger.