BBMG detent alternative

Building or modifying BB, Airsoft, and Pellet type of guns. Show off your custom designs, find tips and other discussion. Target practice only!
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POLAND_SPUD
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Thu Aug 25, 2011 4:04 pm

I'm not too concerned about being economical with airflow, rather optimising muzzle energy
First of all, that's not what you normally say. Secondly the first two designs doesn't offer higher muzzle energy than the third one (the one with a detent)
Looking at the global picture, note that eliminating the detent increases rate of fire, meaning a given target will require a shorter burst (in terms of firing time) to be destroyed, so you're still saving gas
Detent is a detent - you get - let say 500 psi as opposed to roughly 40 psi

Sure the chamber is pressurised when you open the valve. However, the problem here is the delay between openning the valve and the time when the first bb enters the barrel... I have no idea how to calculate or measure that but the pressure will drop


For me it seems you're trying to reinvent the wheel... nope that's not the right term. You designed a gun that is more like a typical piston valve pneumatic rather than BBMG.
You do know that you might as well use an airsoft hopup unit?

I need a "sandblaster" in my armoury though
The problem is see here is shi### performance of 1mm ammo... You might not be able to judge the performance of the gun due to that and its scale...

Choose 6mm (or at least 4.5mm)... build a couple of prototypes and compare their performance.
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Lockednloaded
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Thu Aug 25, 2011 5:04 pm

A little modification to one of your designs, ignore the fact that the BBs are stuck to the top of the cloud chamber

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warhead052
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Thu Aug 25, 2011 5:52 pm

LNL, I think that may work pretty well, except we would need to turn gravity back on :wink:
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saefroch
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Thu Aug 25, 2011 8:53 pm

BBs could get lodged behind the bolt. Moving the air inlet to behind the bolt would solve the problem.
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Lockednloaded
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Thu Aug 25, 2011 9:01 pm

I tried to indicate that the bolt inlet is much smaller then a BB to avoid such a problem
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jackssmirkingrevenge
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Fri Aug 26, 2011 1:08 am

saefroch wrote:Don't mean to get off-topic, but how large is that SCUBA tank and what pressure do you keep it at? I think you mentioned you run 800psi on the outlet of the regulator?
It's 8 litre capacity and I have it filled to 300 bar (4410 psi) - never hooked it up directly to a prototype though, I use it to fill my PCPs (Daystate Mk3 at 210 bar, FX Monsoon at 200 bar) and Ninja paintball tanks (48ci and 13ci, 200 bar) - the latter is where I get my regulated 800-850 psi output.
TRADITIONALIST_SPUD wrote:First of all, that's not what you normally say.


The times they are a-changing' ;)
Secondly the first two designs doesn't offer higher muzzle energy than the third one (the one with a detent)
I would dispute that, more below.
Sure the chamber is pressurised when you open the valve. However, the problem here is the delay between opening the valve and the time when the first bb enters the barrel... I have no idea how to calculate or measure that but the pressure will drop
You have a point, in the sense that the detent is the only way you can guarantee maximum pressure behind the BB at the time of firing. However, it depends at what rate you're feeding air into the BB chamber. If you have say a 3mm barrel but at feeding through 4mm tubing, more air is coming into the chamber than can flow out (especially considering flow is obstructed when a BB is in the barrel) so I think with the correct setup things will even out. Just a theory, I need to try it out :)
The problem is see here is shït performance of 1mm ammo... You might not be able to judge the performance of the gun due to that and its scale...
Again, fair point - but as I said, I need a 1mm "duster" for practical purposes anyway, so might as well try and optimise it. Making an o-ring detent for a 1mm BBMG is not exactly a practical option so I need alternatives.

I know, I know, you want to see the detent-blocker thing work. All in due time :) I definitely want to make it for 4.5mm, trying to figure out the best way of machining it. Trust me, when you get your lathe (it's only a matter of time now :D) you'll know there's more work in the designing that the making!
Magneticboots wrote:A little modification to one of your designs, ignore the fact that the BBs are stuck to the top of the cloud chamber
Image

Putting the breech at the bottom is asking for trouble in my experience...
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Sat Dec 03, 2011 9:05 am

Thinking of a way of making this design practical, here's on idea. The principle is as suggested previously, a BB would jam in the detent, causing pressure to build up in the chamber, causing the piston to compress, blocking off the breech until the BB is fired, depressurising the chamber allowing the piston to return to its rest position and the cycle to be repeated.
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detentblocker.png
detentblocker.png (8.78 KiB) Viewed 840 times
hectmarr wrote:You have to make many weapons, because this field is long and short life
warhead052
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Sat Dec 03, 2011 8:14 pm

I see one problem with that. If the piston is depressed, and air pressure is behind it, wont it get jammed there? And how do the bbs feed into it.
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pneumaticcannons
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Sun Dec 04, 2011 10:18 am

If the piston is depressed, and air pressure is behind it, wont it get jammed there?
I think that the thing that blocks the breech is just a wire(lol I thought it was like a little cup at first too)
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jackssmirkingrevenge
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Sun Dec 04, 2011 1:11 pm

pneumaticcannons wrote:I think that the thing that blocks the breech is just a wire(lol I thought it was like a little cup at first too)
Yep, some mucking around with sketchup later:
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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Gun Freak
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Sun Dec 04, 2011 1:19 pm

There isn't very much area for pressure to act on, that spring would have to be really weak or the area would have to be bigger.
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jackssmirkingrevenge
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Sun Dec 04, 2011 1:27 pm

*cough*850psi*cough*

Even with a 1mm diameter piston there would be a full pound of force pushing on the blocker.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Gun Freak
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Sun Dec 04, 2011 1:29 pm

I'll shut up.

:D

Shame you're just now getting sketch up :wink:
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pneumaticcannons
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Sun Dec 04, 2011 8:49 pm

judging by the bends I'd say he's had it for a while :D
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Gun Freak
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Sun Dec 04, 2011 9:24 pm

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:
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