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BBMG detent alternative

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Unread postAuthor: pneumaticcannons » Sun Dec 04, 2011 10:20 pm

Gun Freak wrote:Bends are rather simple to make, and judging by the random circles on the rod I'd say he's new to the program :wink:

I guess I'm just a fail at sketchup :D
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Unread postAuthor: Gun Freak » Sun Dec 04, 2011 10:23 pm

I guess so, lol

I use it a lot... Used to do 2D work on it but I prefer 3D now.
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Unread postAuthor: pneumaticcannons » Sun Dec 04, 2011 11:11 pm

I guess so, lol

thanks for the words of support :D
I'm actually not that bad... After all my woodshop teach did make me model my entire minigun in it :roll: waste of time because I pretty much just improvised the whole thing :?
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Unread postAuthor: JDP12 » Mon Dec 05, 2011 12:49 am

What about something like this? Whipped it up in inventor quick, didn't add any springs or anything, but you should get the idea.. its a variant of a standard hopup detent with 6 detents circular about the tube. The tube the detents are housed in is slightly larger than the BB itself, so as to allow air passage around it to propel the BB ahead of it (to avoid the issue of an o-ring detent). however this does still waste air slightly..

Or what about a standard hopup system(bb slightly projecting into the barrel) immediately before an o-ring detent? I envision this to help avoid the issue of multiple BBs in the barrel and not receiving air..

Thoughts?
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Unread postAuthor: jackssmirkingrevenge » Mon Dec 05, 2011 1:08 am

Gun Freak wrote:Bends are rather simple to make, and judging by the random circles on the rod I'd say he's new to the program :wink:


:D

The tube the detents are housed in is slightly larger than the BB itself, so as to allow air passage around it to propel the BB ahead of it (to avoid the issue of an o-ring detent). however this does still waste air slightly...


I've pondered this but it's a less-than-elegant solution, unless you can do the math really well.

Ideally, you would have to feed air into the chamber fast enough that time to reach pop-off pressure in the chamber = projectile travel time in the barrel.

I can see it working, but you would need a high flow firing valve and a flow control valve between that and the chamber in order to be able to "tune" it.

One disadvantage (unless you're trying to achieve it :D) would be that rate of fire would still be very high, because there is a minimum flow needed to the chamber for it to fire at all, and this flow is likely to be quite high.

Or what about a standard hopup system(bb slightly projecting into the barrel) immediately before an o-ring detent?


It might work, but one thing I like about the proposed blocker system is that it eliminates the guess work because it depends on chamber pressure, therefore:

- BB in the detent -> blocker activated, no more BBs can enter the breech
- BB not in detent -> blocker returns to rest, a new BB can enter the breech.
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Unread postAuthor: JDP12 » Mon Dec 05, 2011 1:25 am

valid points.. i'm just trying to think of ways to get the "perfect seal detent" i.e. o-ring without the problems of blocking off the barrel.. without a complex bolt system like you have designed..
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Unread postAuthor: jackssmirkingrevenge » Mon Dec 05, 2011 1:32 am

JDP12 wrote:a complex bolt system


I thought it was fairly simple, but the fact that I haven't built it yet means I'm looking for something even simpler ;)
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Unread postAuthor: JDP12 » Mon Dec 05, 2011 1:34 am

Oh it's definitely been simplified down.. but your designs are always a bit complex, and even more so when it comes to testing them... things such as spring pressure, piston area, and clearance issues are a few issues I see with this design. I'm not critiquing your design, just want to try and find something simpler, although I doubt I will.
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Unread postAuthor: warhead052 » Mon Dec 05, 2011 10:50 am

Homemade hop up incorporated? I did that with an oring and a airsoft barrel. About five minutes later with a hack saw I had an adjustable hop up built into the barrel, and the oring also built up a bit of pressure.
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Unread postAuthor: JDP12 » Mon Dec 05, 2011 1:45 pm

The problem with an o-ring an full auto is that the next bb tends to seal in the o-ring, cutting off air supply to the bb currently in the barrel.

EDIT: after doing some thinking instead of paying attention in my thermodynamics class...

It seems this is really just evolving into a full auto blow forward bolt mechanism... So why not just cut out the air/bb chamber and make it a magazine fed full auto? More air efficient, and simpler to manufacture. I'll draw up a quick diagram when I get home..

EDIT 2: After drawing a diagram i realized theres no point to post it, as it looks exactly like the diagram JSR posted with his blowforward bolt a long while back. I feel like this current design you have is simply a more complex design of that, and you could easily modify that for full auto...

Seems like we're trying to reinvent the wheel now.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 06, 2011 1:00 am

JDP12 wrote:I feel like this current design you have is simply a more complex design of that, and you could easily modify that for full auto...

Seems like we're trying to reinvent the wheel now.


I'm not sure I agree.

There detent "valveless" mechanism is hands down the most efficient there is, as I've said many times but I'll list the benefits again:

- zero "valve opening time"

- 100% full flow at projectile motion

- zero dead space

Any type of blow forward mechanism will by definition be less efficient, and need more air at higher pressure to get equivalent power.

The only problem with the detent is reliable and sequential feeding, and I believe this is a simple way to solve the problem.

Shaved the design down a little in the meantime, I think I can give this a go this evening pending some dramatic epiphany :)
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Unread postAuthor: CpTn_lAw » Tue Dec 06, 2011 4:45 am

Hi guys,
A while ago i posted a scheme of a BBMG that wouldn't loose air. Some kind of a full-auto barrel-sealing piston valve.
Let me try to find it back...

EDIT : Found it Image


This was a while ago, like 4 years...
This design is the same as a Nerf machine gun I had when i was kid. It could be done with stronger materials and benefit from the piston type of guns.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 06, 2011 5:29 am

Hah! He's still lurking :D

I remember the thread :)

It would not lose air in the sense that there wasn't an exhaust valve (same as my pop-off design really) but you still lose air with whatever bolt mechanism you choose to make.
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Unread postAuthor: JDP12 » Tue Dec 06, 2011 11:14 am

Oh.. doh. I'm an idiot. *Wanders off to wonder if engineering is really the degree for him*

Well now that I figured it out, I definitely like that design and think it would work very well, can't wait to see results..

If I may make one suggestion, make the back part of the spring/plug housing removable so you can swap out springs. Since you may not get it right the first time, saves you from having to build a whole new assembly.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 06, 2011 1:17 pm

JDP12 wrote:Oh.. doh. I'm an idiot. *Wanders off to wonder if engineering is really the degree for him*


I'm sure it is :) you're on spudfiles!

If I may make one suggestion, make the back part of the spring/plug housing removable so you can swap out springs. Since you may not get it right the first time, saves you from having to build a whole new assembly.


Yup, the back plug will be removable. I need to reload it somehow anyway :) machining the prototype as we speak, it will still need epoxy though so testing will have to wait 24 hours.
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