Plaster casting .408 cal

[BoyntonStu]

There is a rubber-like coated marble round sold for police use that is specially sized for their barrels.

http://www.airgununiverse.net/community/index.php/topic,335.0.html

Another possibility is to mold in some spiral grooves to make it spin.

[mouz]

you know how a lapua magnum bullet has six bands around it?


http://www.targetsportsmagazine.com/js/tiny_mce/plugins/imagemanager/files/2008/February_08_/SPORTS_STARS/338_LM_02.jpg

[FighterAce]

There is a rubber-like coated marble round sold for police use that is specially sized for their barrels.

http://www.airgununiverse.net/community/index.php/topic,335.0.html

Another possibility is to mold in some spiral grooves to make it spin.

That would be very hard and expensive... trying to match spiral rubber lines on the bullet with the barrels rifling without knowing if its got the right twist rate.

you know how a lapua magnum bullet has six bands around it?


http://www.targetsportsmagazine.com/js/tiny_mce/plugins/imagemanager/files/2008/February_08_/SPORTS_STARS/338_LM_02.jpg

Yes the bands cut into the rifling to make it spin. If I tried that with plaster, they would break off and fill up the whole barrel with just a few shots sent downrange.
For rifling I use a hexagonal nut. That means if I put 6 short lines or bumps around the bullet at equal intervals in the direction of the rifling, they will seat in the rifling grooves, make a possibile 100% seal and make it spin 
The trick is to get the bumps raised enough and for that I'll need to find out how deep my rifling tool cuts into the barrel...
Makes any sense?

[boar]

might rifle a short section of scrap barrel tubing take a cast from then turn your bullet from that

Boar

[FighterAce]

For that you need to cut your barrel length wise in half. Now if you cut you remove material and when you join the 2 halves back together its no longer a perfect circle, its an ellipse. Oval bullet is not a good fit in a perfectly round barrel 

[mouz]

well you cut the barrel piece with a saw of a known thickness and ad the material back on. an expensive idea: cast grooves in the bullet and but O rings around it...... a very expensive idea. you could also cast grooves in the bullet and wrap the groove with a couple turns of electrical tape, it will stick to itself, and if you wrap it tightly it will hold.

[FighterAce]

Nice thinking mouz  Too bad I already thought about all this before you posted it. Casting a recessed area for the tape would be a good idea but expensive. I'd need to apply a release agent for every single pour, not to mention the cost of the tape and time to wrap every bullet.
Casting an O ring groove would actually be a better idea but still I'd need to use a release agent and buy a lot of O rings. Just one thing to note... the O ring will have to adapt to the rifling grooves. To do that, the O ring must be as high from the plaster as the rifling  grooves are deep. If you do that then the bullet becomes unstable in the barrel, just like a nail dart. You never know where the tip is pointing. Again, to solve this you need to add more O rings witch adds cost and who knows what kind of aerodynamic properties.

But why even bother with all that if I can make everything out of a single piece of plaster.

[boar]

i dont think you would need to cut it long ways i think you could push it out thre rifling should make it twist out it might take several tries but its only a small part and you only need 1 to turn down then make a mold from might try a harder plaster at least for the plug if the rifling tears out on demolding
Boar

[mouz]

if you made the grooves shallow and long you wouldn't need a release agent. you could have two. the way i do it is i cast the bullets, in a few hours take them out of the mold, and file a groove around each bullet then wrap in tape, what else do you do while you wait for the next batch to dry? it takes less time and effort than it sounds like it does. the way i get mine out of the mold( two pieces of wood with 9 holes drilled between them and clamped together) is i stick the point of knife beside the bullet and pry it out. this would fine with grooves built in.

[FighterAce]

what else do you do while you wait for the next batch to dry?

I leave it alone for awhile, live my life. What do you expect me to do, sit and watch it harden for 1 hour?

Filing grooves by hand is a labour intensive process and in my mind, not worth it. For the hundreds or even thousands of rounds I plan on making, your approach just wont do it for me. Everyone has different goals and different approaches to different problems. If something is good for you doesnt mean its good enough for me.

btw. doesnt the knife damage the cast?

[mouz]

no, the knife doesn't. my slugs are NOT perfect. i have nothing else to do, my air guns are born of boredom. why you might ask do i need a .52 caliber musket for shooting tin cans?!?!?!?!? cause i got nothin' else to do. you have different needs than me. i need a crude slug for a non rifled barrel. you need the perfect bullet for a rifled bore. i think you should use hydrocal.

[boar]

hydrocal is good stuff ive used tons and i mean that literaly of hydrocal 30  whilt that night be what he needt to get the original plug i think plaster of paris may meet his needs for production hmm bondo might be good for a slug cast that would be machinable to take a mold off of


Boar

[FighterAce]

Interesting... It might blow the cost effectiveness away but hey.. if I can get that much more of a punch when it gets there I bet ya its worth it. I should get some experience with my cheapo plaster first  Not to mention, get it to fly straight

[Forum Admin]

I leave it alone for awhile, live my life. What do you expect me to do, sit and watch it harden for 1 hour?

That was the first thing I read this morning, I laughed so hard, I've got tears running down my face.  Keep up the good work on the project, I'm very interested in seeing how these bullets work and what twist rate will stabilize them.

[paintballarmsdealer]

Did you fine any rubber? I saw some on e-bay being sold out of Italy