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Why 6/8mm?

16960 Views 62 Replies 10 Participants Last post by  Cheese Man
Why has airsoft stuck to the 6/8mm (hardley 8mm anymore) platforms? Is it to preserve safe MEDs? Is it because if we went bigger there would be too much mass? Or is it just because the industry has decided that for us?

I have been looking into custom BB designs for a project and designing custom 6mm BBs is just damn small. Then I contemplated going to 8mm. Most recently I have been thinking about going as large as ~10mm (0.40cal. to be exact). From varous topics I have read I can see a few problems/hesitations for going so large, the main concern most likely being that increased mass = increased MED/more safety concerns.

However, I would pose that for a sniper role, since our MED is longer anyway; a slightly larger round at the heavier range of existing BBs (0.4 - 0.5) would be able to be fired at a lower FPS with greater stability resulting in better range and increased accuracy. Wheter it would be custom 8mm rounds or going as large as what I am thinking I don't know, but its just a thought.
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Generally plastic of this kind would be of bad quality would it not?
sniperninja said:
They have plastics that don't need heat, you just mix and pour it into the mold.
I can imagine it wouldn't be the greatest quality... but... if it is some form of simple epoxy resin it could be pretty amazing stuff... as far as precision/weight go I'm not sure, but it'd be worth a shot over trying to make a precision injection mold, especially since I cant think of any way to break it down to less than 3 parts, and 3 part molds get very very... very complex to deal with :-/

Edit: Advantage to an epoxy based over an injection mold (if it is epoxy) would be that if it is done cold, epoxy generally expands in the curing process, where as with an injection mold there is always the possibility of air pockets getting stuck in the mold, causing the injection material to combust/the material contracting when cooling; all resulting in imperfections in size and tolerances. Professionals have very complex machines to get the consistency they do, i.e for mainstream BB production, however even for a store bought personal home press you run into a lot of these issues if you are trying to make precision parts.
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bobgengeskahn said:
ME as in Mechanical Engineering.

I think boat tail, mostly because it work very well with match grade RS bullets.
And this is my thinking for trying it, however the seal that is created in RS vs. the 'seal' (or lack of) that is created in airsoft may cause an unacceptable bleed of pressure. The other concern I have with a boat tail would be exposing the fins to the air flow from the cylinder (planning for a HPA set up) would cause the BB to rotate counter to the intended spin once it leaves the barrel. I may just be over emphasizing the effect in my head... all the more reason to test

On a slightly more serious note, I have been looking all day and have yet to find a way to build an acceptable mold. I have mainly been looking into injection molding and some rapid prototyping techniques. Anyone have any ideas for an accurate cheap way to cast things?
damn. You had me all excited for a second xD

Before you have a mold, don't you need something to mold with?
If possible, what about a CNC'd mold? Probably a one piece that would need the flashing sanded, or a totally CNC'd piece of ammo? Thought that would be expensive.....
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There are a few ways to make molds depending on the manufacture process you're going to use. Most likely since this would be a "garage style" build I'll have to get one pellet built out of 7075 or some sort of steel and use that to cast off of... and it honestly wouldn't be that difficult as long as I can draw it in CAD first (I know some people that would be able to cut it, might take a while, but free is worth waiting

Another possibility would be to go straight to the mold and design that on CAD and have it cut, but like I said, designing a 3 part mold is very difficult to get right, especially on a 6mm by 12mm round, or even if I go to a 8mm. (I am still looking for a 10mm/0.40" tube since that is where I'd like to end up, just cant find anything precise enough to be the barrel, so if anyone knows anywhere...)
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Slice and dice some cheap stock barrels? Or totally off?
If you found an IB with an outer diameter greater then 11mm, you could drill it out to 10mm, but it could easily be bent.

10mm brass tubing, but I think its a 10mm OD, doesnt say :X
Unfortunately with both of these ideas is that if I were to bore a stock barrel the wall would be too thin (stock barrel OD is usually only about 10.5mm) and I couldn't assure 10.0mm +/- 0.001 or even +/- 0.01 with a drill that long.

I have found some 10mm ID tube (tube is measured by OD, pipe is measured by ID for those that may not know the difference), however they only guarente accuracy down to +/- 0.05 usually or worse, which in airsoft barrel terms is HUGE as most of us know
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I found aluminum at 6.04. That is as close as I could find aside from 5.90. I looked for weeks for steel brass and aluminum. I did however find carbon fiber barrels in 5.98. When I called the guy was away on a family emergency.

I bet there is tubing in 8mm ID though. Many sites post both ID and OD or OD and wall thickness.
If I can find a precision 7 or 8mm barrel I'll try to go with that, but the barrel hunt will have to wait till I can decide on an actual size for the BB.

I have spent most of the day looking at different casting techniques and started reesarching different .410 sabot/slug designs. There are both rifled and unrifled slugs for the .410 and it seems from the forums that I have read that the rifling on the slug does not actually spin the slug at all and is more for looks than anything else. What do you guys think? I have not heard anything else either way, however after thinking about it I could see it going either way. On the one had it would make sense that curved v. straight cuts would make a difference, on the other hand the control surfaces would have to be rather large to make a difference.

My original plan was to make rifled rounds and find a way to hook up a high speed video along the flight path to see if they actually did spin... but for ease of manufacture it would be nice if I could clear this up before custom building a rifled mold (because that would only be about 10x the cost and about 100x the headache of not rifling it
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This might be a stab in the dark, but does anyone have a picture of the cross-section of a TK Twist barrel? Either 6mm or 8mm. I am debating a slight change to design, but right now it remains a tangent...
The only pics of that are looking down the barrel im pretty sure.
For those still interested in this, I have been able to locate TB 8mm barrels, so I think that is what I will end up going with. They have to ship from Japan though so it will be a while, however I am coming close to a BB design, hopefully I'll be able to get some casts done before the barrels get here.
Awesome. You are awesome.
Sadly this is going to mean I won't be able to send you guys any to try out... well, I could, but you wouldn't be able to shoot them unless you have an 8mm laying around. But if someone does let me know because I'd like to see how a hop up will effect them since I am not planning to have one in the build I am hoping to do.
Why not buy a cheap as chips second hand .22 air rifle and hack the barrel off that? It will be pre-rifled for you!!

As far as making the ammunition is concerned I dont know how they make BBs so smooth and shiny, but I would avoid a rapid prototyping machine as the surface of the shapes they produce is very grainy, you would end up with dimpled BBs after all!!
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What are you going to be making the pellets out of? Unless I am missing something major here...
This is how BBs are made:

All BBs, reguardless of brand, are typically made in 3 or 4 major factories in China. The defining factor that you pay for is the polish quality and precision in the molding process. The polish is typically done in a tumbler with a polishing powder in it (like super fine sand).

The materials that I am looking at are... different. There are certian characteristics that I need for my idea to work, so I have a few things in mind that I am going to try, but nothing solid yet that I really want to discuss yet ;-)
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