Plaster casting .408 cal

[FighterAce]

I'm attempting to make .408 cal replica bullets out of plaster to shoot out of my rifled barrels. I've made a wooden one to make a mold from.






Now I gotta get some epoxy for the mold and plaster to start casting. I feel like I'll need to make a few more rifled barrels to get it fly straight 

[BoyntonStu]

Looks promising.

My concern is how well the plaster will hold up on impact.

Is the plaster the projectile or the carrier?

IOW What percent of the projectile weight is the plaster?

Could it be cast as a hollow shape?

You do excellent work.

P.S.  Check out the accuracy of this smoothbore air rifle and the ammo that did it.

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

[FighterAce]

I just got back from the store. Got 2 packages of epoxy resin and 1kg of plaster. Gonna make my mold now and hopefully first rounds tomorrow morning.

The plaster is just an aerodynamic shell that carries a 7cm nail hidden inside. The theory is that upon impact the plaster will shatter and the nail will penetrate the target... if its armored of course. The plaster will probably survive penetrating a soft target. I dont think I'll be able to do a hollow cast but I'll certanly try.

My concern is plaster catching the rifling. If it doesnt, the bullet will tumble.

I have no idea of the weight since I havent got a digital scale. I'm guessing the percentage of the plaster in bullet weight will be about 80%

[FighterAce]

I'm having problems with epoxy casting so I'm gonna try wood putty since I have so much experience  with it. Plus its way cheaper and easier to manipulate 

[mouz]

this is a really great idea! i hope it works!

[mouz]

i just cast some plaster of Paris bullets and they seem pretty effective just as plaster, enough to blow a huge hole in a tin can anyway. i cast some with a bunch of little nails inside, but i have yet to test them. i also cast one with a single large nail, the plaster shattered upon impact, but instead of penetrating the target the nail ricocheted back at me! this was cause the plaster is so hard that all the energy is used breaking it. i think a bullet with a ball bearing in the plaster would be much better, especially if it is only half cast in plaster and the other half is sticking out.

[FighterAce]

Here is the first one  





I still need to touch up the tip of the mold and sand the entire thing for about 1mm because its a wobbly fit in the barrel. I cant test fire it anyways because the check valve stop on my pump melted. I ordered a new one to be made out of stainless steel.

[Forum Admin]

Looks like it turned out quite well for the first one.  I'd be interested to know how it performs in that rifled barrel you made as well as what it can do to a target. 

[mouz]

do some tests! hey, i want to know, how big is the inside diameter of you barrel? 

[FighterAce]

My barrel is a dead on .50 cal. I cant do any tests.. I already told you... the one way valve on my pump melted so I'm unable to pump at all    Its gonna take at least a few weeks for the part to be made.

btw. I found this calculator online... http://kwk.us/twist.html but I have no idea what SG value to put in. I'd rather believe this thing then trying to rifle at the correct rate by trial and error.

[BoyntonStu]

Here is the first one  





I still need to touch up the tip of the mold and sand the entire thing for about 1mm because its a wobbly fit in the barrel. I cant test fire it anyways because the check valve stop on my pump melted. I ordered a new one to be made out of stainless steel.

Your work is absolutely superb!

[FighterAce]

Your work is absolutely superb!

Thanks  I hope my rifling is too.. otherwise my work over the last few weeks was in vain

[FighterAce]

I got good news and bad news..

The good news is that the bullet does accept the rifling in a pvc barrel. I'll just have to make sure if thats true when its going very fast.

The bad news is that it leaves a lot of gunk in the barrel. I'm hoping the air blast will clear it out....

all thats left is to get my pump going and check if the rifling has too much/little twists... hoping to see some really tight groupings soon

[mouz]

i would suggest making the ammo a bit loose and wrapping with a thin layer of tape.

[FighterAce]

I already thought of this and came to the conclusion its a very very bad idea. This bullet soley relies on aerodynamics and spin for stability. If I introduce anything to the streamlined shape it could tumble even if I get the rifling twist rate right. Then I thought of making a groove on the bullet itself for the tape to rest in but then it would be almost impossible to extract it from the mold in one piece since I have to push the bullet forward.

btw. if you havent tried already, tape doesnt stick to plaster at all, it just falls off 

I've been thinking how the paper cone expands when you fire it and adapts to the contours of the barrel. I wish I could somehow adapt the same thing to solve the sealing issue.
First I thought of inserting a paper cone in the back of the bullet while the plaster is still watery to give it a better seal but quickly realized that the .408 bullet has a slightly tapered end to "calm" the airflow at the back making it more stable.
Any ideas? And no I'm not putting anything behind the bullet to push it like a tight fitting cork...