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M82A1 0% (destroyed)

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: Demon » Tue May 10, 2011 12:47 pm

No matter the front ejected sabot, discarding sabot, or plain wadding, the projectile spins.

Rifling is the only way to fix that.
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Unread postAuthor: jor2daje » Tue May 10, 2011 4:29 pm

Is the part of the reducer that hits the sabot perfectly flat? If it isn't it might hit unevenly and shift the projectile at the last second?
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Unread postAuthor: Demon » Tue May 10, 2011 4:52 pm

I wil repeat for the third time, no matter how I launch, spin is created (And it would seem that it happens at the muzzle of the barrel). Putting gradually bigger holes at the end of the barrel won't change anything since the projectile, on front of the sabot, gets out of the reducer's smaller hole before the sabot's rear exits the barrel.

On one lucky shot (that had no imparted spin on it), the projectile managed a bull's eye @ 65 meters (soda can).

I tought that, with a 80 centimeter barrel, I would've had gotten better results (At least at 100 meter, hitting a man sized target).

The project is on hold until I find how to get a decent accuracy at each shot
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Unread postAuthor: FighterAce » Tue May 10, 2011 5:33 pm

65 meters with a screw and nut? How did you stabilize it? Are you sure its not tumbling end over end?

What if you put a strong spring at the end of your barrel so the sabot doesnt stop so suddenly?
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Unread postAuthor: Demon » Tue May 10, 2011 5:36 pm

The projectile is simply heavy enough not to be any problem IF there is'nt that goddamn-coming-out-of-nowhere spin.
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Unread postAuthor: FighterAce » Tue May 10, 2011 6:10 pm

So basically, if you got enough power you can fly a brick :D

Maybe as the sabot hits the stop and the projectile starts to come out, the sabot tilts due to the impact and nudges one side of the projectile making it spin. Try a different stop, reduce the projectiles length thats inside the sabot and maybe smooth the projectile a bit? Filling the gaps with epoxy or something... that would also be a good way to make them all the same weight.
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Unread postAuthor: saefroch » Tue May 10, 2011 6:42 pm

I know this is really unlikely, but it might be possible that it's the interaction between the exposed threads and the sabot that is imparting the spin on the projectile...

Have you done any filming to determine if they're tumbling or spinning as if the barrel is rifled?
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Unread postAuthor: Demon » Tue May 10, 2011 6:56 pm

Accuracy's good enough for where I can shoot anyway ...

But a new :idea: just popped in my head !

http://www.google.ca/imgres?imgurl=http ... 29,r:0,s:0

Long link FTW !

A VSS Vintorez (pop-off based) using the energy of the front ejecting sabot (The sabot will be ejected upward this time) to load the next round.

Will shoot full auto with airsoft .3 gram, and all the ejecting sabots will look like spent cartridges. !!11!!one!!one11!!!!

It will be awesUmeZ !

But that does'nt mean I stopped working on the asthetics of the M82A1. It just will take more time.
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Unread postAuthor: hi » Tue May 10, 2011 10:16 pm

What if you just shoot a marble or ball bearing? it doesn't matter if that tumbles...
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Unread postAuthor: jackssmirkingrevenge » Wed May 11, 2011 3:54 am

The projectile is simply heavy enough not to be any problem


False.

Your projectile is unstable, end of.

Unless it's a perfect sphere you can't expect it to tumble in air without significant effects on trajectory.

If you can get the sabot to impart enough spin to the projectile, rifling the barrel could potentially make a difference.

Otherwise as suggested above, use spherical shot.
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Unread postAuthor: Demon » Wed May 11, 2011 5:55 am

The spheric projectile was spinning crazy at the exit of the barrel.
This is not the case anymore for the cylindric one, as it spin slower or barely.

Accuracy is'nt what I dreamed of, but anyway I have no decent shooting range. (I get 60 centimeter deviation at 65 meters with the simple bolt, as opposed to sometimes more then 10 meters with the spheric one).

It would seem sabots are the ennemy of unstabilized projectiles ...

I have a concern, tough. If ever I rifle the barrel, will the cylindrical projectile (.3 mm per 20 mm) will respond well to it ? Are there any physics associated with the shape of the projectile that comes out of the rifled barrel, or it does'nt matter ?
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Unread postAuthor: jackssmirkingrevenge » Wed May 11, 2011 7:01 am

Demon wrote:The spheric projectile was spinning crazy at the exit of the barrel.


How can you tell?

This is not the case anymore for the cylindric one, as it spin slower or barely.


Again...

It would seem sabots are the ennemy of unstabilized projectiles ...


Before you blame sabots, have you tried firing your projectiles through a barrel that fits them exactly, without the need for wadding?

I have a concern, tough. If ever I rifle the barrel, will the cylindrical projectile (.3 mm per 20 mm) will respond well to it ? Are there any physics associated with the shape of the projectile that comes out of the rifled barrel, or it does'nt matter


It has more to do with the length and weight distribution of the projectile, look up the Greenhill formula, there are several online calculators: http://kwk.us/twist.html
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Unread postAuthor: Demon » Wed May 11, 2011 9:00 am


The spheric projectile was spinning crazy at the exit of the barrel.



How can you tell?

This is not the case anymore for the cylindric one, as it spin slower or barely.



Again...



Are you serious ? You think I can't tell when the projectile makes a 90 degre turn ?
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Unread postAuthor: jackssmirkingrevenge » Wed May 11, 2011 10:21 am

Demon wrote:Are you serious ? You think I can't tell when the projectile makes a 90 degre turn ?


You mean you can actually see it spinning, or are you getting "keyholing" in the target?
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Unread postAuthor: inonickname » Wed May 11, 2011 10:23 am

Demon wrote:

The spheric projectile was spinning crazy at the exit of the barrel.



How can you tell?

This is not the case anymore for the cylindric one, as it spin slower or barely.



Again...



Are you serious ? You think I can't tell when the projectile makes a 90 degre turn ?


Not when the projectile is travelling that quickly, and will appear the same, spinning or not...

Do you mean something else? Eg. Is the projectile "looping" around.
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