Bullet moulding help

Shangti

New Member
Hi guys I am hoping someone could help with a newbie moulding person. I have a 3D print of a 40k Bolter round that I want to duplicate.

The majority of the rounds will be single piece, (these are simple 1part pour moods) but some of them I want to be spent rounds.

My question what’s the best way to cast the spent shells? I have seen people using a core inside the hollow tube then making a 2 part mold, also seen 3 part molds with a plug. I am planning on using smooth-on 20. Any help greatly appreciated.
 
A spent round can be one piece as well if you use an appropriately stiff RTV. Alternatively, mold the lip as a shallow depression, with the center marked and bore out with a drill.
R/ Robert
 
The problem I have is this is extra large ammunition (the bolter I am making is almost 1m in length). The round is about 100mm long and 32mm diameter, it would be a waste of material to solid cast and then bore it out (plus i dont have anything that big for the job). I did debate sluch casting with a one piece but it wont be nice and smooth inside.

Sorry I dont know why this image keeps coming out on its side, I've rotated it and still does this. Anyway you see the size if it now


IMG_5658.JPG
 
You're going to have a difficult time. The bullet and the casing have undercuts that would make removal from a mould either difficult or would cause ripping of the mould. You would need to make a 3 piece mould if you want the casing hollow. Or you could get away cutting the casing in half and make a 2 piece mould on each piece and just glue the halves together.

TazMan2000
 
"Sorry I dont know why this image keeps coming out on its side, I've rotated it and still does this. Anyway you see the size if it now"

Default horizon VS portrait. The longest side, left to right. crop it so it is shorter than than wider should do it.
 
I have always used brass open tubes, depending on the scale I work in. for one side to simply use filler and blacked paint like brass, with a pin hole in the center. then just cast it to the ground .
 
Cool thanks. I figured it might be a 3 piece, nothing like starting at the deep end.

Cheer peoples

After thinking about it, my advice for a three piece mould might not be wise. If you're moulding a 3D print, you're going to have some texture, that will cause a lot of friction and resistance to pulling out the RTV that goes into the cavity even if you use mould release. The possibility of ripping the RTV "cylinder" off is great, unless you have the cavity tapered to the bottom. Perhaps cutting your master in half, making two piece moulds of the halves and then gluing the halves together might be easier. You could always try the 3 piece...the only thing you would lose is some RTV and time.

TazMan2000
 
You might have to use trial and error to find the right mould. Sometimes it cannot be avoided, but I try to avoid mould seams anywhere that is going to be a beast to clean up later. From your picture above I cannot tell if the casing is closed at the bottom... if so I would make the bullet out of 3 parts, a nose that sticks into the cylinder on the top and the bottom ring sticking into the cylinder the same way from the bottom. the nose and the butt are relatively easy to mould and cast... as for the cylinder I would try the following...

I would try a 2 part mould by filling the cylinder center with silicone first. Make it a bit longer than your casing on both the top and the bottom and give it a fairly good locking texture at the bottom so that you can set it inside the second part of the mould without any wobbling. You might want to taper it a very little bit so that it is easier to connect the two mould parts. You can "extend" your center mould on the top/bottom with any wide tape. You also might want to use tape to cover the entire inside wall of your casing and get rid of any relief on the inside... that will make it easier to pull the silicone out later. It might require a bit of fiddling, but you should also be able to get away with placing your main pouring channel for resin in the center silicone part as well.

Once you have the center part of your mould finished, build a cage to contain the outer silicone. I use LEGO for this because you are very flexible in terms of size and form and they are re-usable. Take the tape off the bottom side of the mould, I would leave it on the top side to serve as the escape channel for the resin, make sure that the tape is thick enough for this purpose. Once you have the cage finished, use talcum powder to dust up everything and pour the outside part of the mould.

When your cast is cured, you should be able to pull the cast with the center mould out and then pull the main pouring channel out from the center like a sword from a sheath, that should also make it easier to then remove the center silicone from the cast by pushing gently on one side and pulling from the other.

I hope that helps and my description is understandable.
 
Last edited:
Wow, thanks dude. Sorry its taken so long to see this, didnt get a notification. I will give it a crack next month hopefully and let you know how it goes.
 
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