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Resin Casting Ammo?

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Resin Casting Ammo?

Unread postAuthor: bobgengeskahn » Sun Jul 17, 2011 11:41 am

Hello everyone, it's been a long time since I've posted around here but I have something that I think the people on here would know best about.

I am currently working on a rather extensive airsoft (6mm) HPA redesign project and in working backwards have decided to attempt making my own ammunition.

The peramaters are as follows:
Mass: ~0.3g - ~0.5g max
General description: D = 6.00mm 4mm parabolic cone as the nose with a 2mm section at 6mm with a 3mm long boat tail at the rear.
Other: I would like to use a material that has some give to it since I am planning to use it in a rifled barrel, so it has to be able to take the rifling. In addition the tolerances are pretty tight, so something that would have minimal shrink in the cooling process would be idea.

Since it is so small I am looking at either casting or injection molding with some kind of polymer. In the reading that I have been doing and bearing in mind that this is wholy DIY and I don't already have a desktop injection molder, I am leaning toward casting with resins for a few reasons. Mainly because the mold is simpler and there tends to be less shrink with resin casting. The down side is that cure times are dramatically longer and there are no data sheets that I can find that can give me enough information to estimate the final weights.

Any input that anyone here has about working with pastics, injection molding or casting would be greatly appreciated. I searched around and found some valuable information here, just nothing at this scale or with the level of precision that I am looking for. Thanks!
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Unread postAuthor: spudamine » Sun Jul 17, 2011 12:21 pm

density for most cured epoxy systems is anywhere between 1 and 2 g/cm^3, Check out somewhere like this, http://www.resins-online.com/ they sell a wide variety of epoxies and polyurethanes such as marine grade and electrical and most of the products have data sheets which will give you the density (specific gravity) and the % shrinkage. (don't buy anything there but it's a useful resource).
Cure time will be an issue, decent epoxies generally have a long cure time, which can be accelerated with curing above ambient temperature but at the cost of more shrinkage.
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Unread postAuthor: bobgengeskahn » Sun Jul 17, 2011 1:30 pm

Thanks! There is a lot of good information there I look forward to reading.

As a side note, if anyone has any information about working with HDPE that would be really interesting. I have seen it used in those white Nalgene bottles and it looks like it would be perfect for what I am looking for in terms of physical properties to take the rifling, although it might be a little light...
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Unread postAuthor: Gippeto » Sun Jul 17, 2011 2:19 pm

Made these for my copper gun...I DO have a table top injection molder. :D An aluminum plate with an 1/8" sprue hole sits on top when in the molder.

Another fellow made a mold and was using it to cast urethane ammo. I'll see if I can find the thread for ya.

Edit: Pictures... along with Nova, are gone. :( Might still be a little info to be gleaned by reading through it though. IIRC, the mold cavity was simply drilled into an aluminum block, with the outer edge relieved with a countersink. Left a small "wedge" shape around the diameter of the base when cast.

Would suggest if you go this route, to make the bulk of the pellet bore riding, and utilize the driving band at the rear to engage the rifling. 5% of total length as a max width for the driving band I would think.

http://www.spudfiles.com/forums/pimpin-ammo-t9989.html
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Unread postAuthor: bobgengeskahn » Sun Jul 17, 2011 3:18 pm

Awesome thread, its killing me that the photo links are bad though!

I do remember seeing your ammo before, but like I said, I dont have an injection molder :cry: and the round I am thinking of seems like it would be a little more complicated to make a mold of (I really have no idea, this will be the first mold I've ever made). What kind of performance do you get out of these? Another idea I thought of was simmilar to the Lees slug round; but I was afraid of the mass being too low and complications with the loading process (I don't really want to deal with shells if I dont have to).
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Unread postAuthor: Gippeto » Sun Jul 17, 2011 5:49 pm

The all hdpe rounds weren't accurate, and I only made a handful at the time. The other hdpe rounds had a 3/8" ss ball bearing in the nose. They worked not bad. Typically hitting "can full of water" type targets at 10 yards reliably.

The lead rounds were good for punching holes in plywood. :twisted:


As far as making a mold for what you want...what do you have for tools?

If all you have is a hand drill...I'll save you some trouble and tell you right now that you're wasting your time.

You need at a minimum a drill press with vise. Proper machine tools (lathe and/or mill) would make it easier.
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Unread postAuthor: bobgengeskahn » Tue Jul 19, 2011 1:32 am

Right now all I have is the typical assortment of hand tools, drills and a dremel (assortment of saws and such, but those aren't really applicable to this). Although I have decided that this would be an excuse to get a decent drill press (most of the ones at local stores though are just cheap build quality :( ). If I need access to a lathe and/or mill, I could probably get access to one, it would just take timing to get time on it.
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