long range ammo MiniBoy Mark I

[MrCrowley]

Why is there a problem where shooting this sabot round is concerned? Is it too heavy or something? I don't see how it would cause a problem when you've shot the cannon before. What size is your barrel and what threads are attaching it?

It will be at least 50g heavier than any other projectile I've fired before. Muzzle energy is expected to be around 7,500 ft/lbs according to HGDT.

Not only that but until recently, the piston used to open prematurely but now that has been fixed so it takes a lot more pressure to open. I've never fired a projectile over 50g since the piston has been fixed.

I guess you could epoxy a short bit of threaded galvanized thread directly into the barrel. The steel would take care of the stress around the crack, and the epoxy joint should only see shear stress, which should be negligible for the reasons above (except perhaps recoil forces. Use a barrel brace to mitigate this)

That's an idea worth checking out. I'll have a look in the garage today and see if there'a anything I can use.

Edit:

I'm lead to believe 40mm threaded fittings have a outside diameter of no larger than 48.3mm. Perhaps I could sand down a bit of the aluminium barrel and get some 40mm threads welded on to it. I believe welding can weaken aluminium though, still a plausible idea?

[Moonbogg]

Why is there a problem where shooting this sabot round is concerned? Is it too heavy or something? I don't see how it would cause a problem when you've shot the cannon before. What size is your barrel and what threads are attaching it?

It will be at least 50g heavier than any other projectile I've fired before. Muzzle energy is expected to be around 7,500 ft/lbs according to HGDT.

Not only that but until recently, the piston used to open prematurely but now that has been fixed so it takes a lot more pressure to open. I've never fired a projectile over 50g since the piston has been fixed.

I guess you could epoxy a short bit of threaded galvanized thread directly into the barrel. The steel would take care of the stress around the crack, and the epoxy joint should only see shear stress, which should be negligible for the reasons above (except perhaps recoil forces. Use a barrel brace to mitigate this)

That's an idea worth checking out. I'll have a look in the garage today and see if there'a anything I can use.

Edit:

I'm lead to believe 40mm threaded fittings have a outside diameter of no larger than 48.3mm. Perhaps I could sand down a bit of the aluminium barrel and get some 40mm threads welded on to it. I believe welding can weaken aluminium though, still a plausible idea?

The weakened aluminum should be OK still since the stress in that area should be mostly tensile, and it would take a lot of projectile friction to cause the aluminum to break in tension. The pressure holding ability, or hoop stress in the welded region should also still be very strong since it is a small diameter. The aluminum will be around 15,000psi yield in the weld area or whatever 6061-0's yield is. Find 6061-0's yield strength and use that to calculate your safety factor for the heat affected zone of the barrel. Welding essentially anneals the aluminum back to its non heat treated condition.

[MrCrowley]

Thanks for that info. I could also get a 50mm threaded adapter and see if it would fit over the 50.5mm barrel. If the gap is too big, I could epoxy it on but if the fit is perfect I'd get it welded.

Then I would only need to buy 2 square meters of fibreglass or so and layer the first meter of the barrel.

A barrel like this could set me back $50USD including adapter, fibreglass and any epoxy/welding. I'd feel a lot safer than using the ABS barrel I 'spose.

[POLAND_SPUD]

A barrel like this could set me back $50USD including adapter, fibreglass and any epoxy/welding. I'd feel a lot safer than using the ABS barrel I 'spose

or be a man and get a proper steel or aluminium barrel

Don't say I can't find them - they are somewhere out there but you haven't found them yet

[MrCrowley]

I'm sure I could find them but I would have to go to the trouble of finding them seamless (for steel), the right diameter, reasonably priced and willing to sell by the meter.

I imagine I would still need to get threads welded/machined/epoxied too.

[Moonbogg]

I'm sure I could find them but I would have to go to the trouble of finding them seamless (for steel), the right diameter, reasonably priced and willing to sell by the meter.

I imagine I would still need to get threads welded/machined/epoxied too.

There are other ways to fasten the barrel. If you can manage to seal it with o-rings, you can secure it with set screws.
But about the concern for the barrel breaking...is the concern your safety or having to replace the barrel? You can fire from a distance and hope it works to fire the special round, and if it breaks then you will be forced to replace it with a better one anyways.

[MrCrowley]

My only concern is safety. The barrel only cost $50 (back when I had money haha) so I wouldn't be too bummed about replacing it.

I could remote fire it, would just need some sort of stand/holding apparatus. The recoil pipe coming off the side would help in some way i'm sure and since I only need to fire it at an angle of 10-15 degrees, it could be fired from the ground.

[Moonbogg]

Yeah, if thats the case then just remote fire the thing. If it breaks you can then replace it. If it doesn't break, you can then be considered lucky and replace it anyway.

[Gun Freak]

If it breaks it screws up the shot and possibly loses miniboy

[MrCrowley]

OK so I've had some time to collect my balls from the ground and now I'm feeling a little more optimistic. I managed to thread the ABS adapter in to the malleable iron adapter completely. If I can then epoxy some metal fitting on the inside of the ABS in that area, I'm sure it would survive.

If I then fibreglass 1m of the barrel to a thickness of 1.5mm and then use another cloth to fibreglass the first 0.5m of the barrel to 4.5mm thick, I should be sweet... I hope.

Remote firing may still be on the cards as 10kJ (7,500 ft/lbs) is uncharted territory in terms of handheld cannons I believe.

Several days before the launch I will do test firings with 100g projectiles and I even have a 150g steel ball bearing to test if I can find a suitable target.

[Moonbogg]

Remote firing may still be on the cards as 10kJ (7,500 ft/lbs) is uncharted territory in terms of handheld cannons I believe.

I'd be a moron not to agree. Don't even mess around here with this thing at those forces, its not even close to being worth it. Remote fire that biotch and stay hella far back.

[MrCrowley]

Since I don't have long between finishing university for the semester and the estimated launch date, I've been thinking about every minor detail of the launch to insure I account for it.

Once everything is set up on the beach and there are no civvies in site, I will do a test fire of a 100g frozen lemon. This will be to check the ignition isn't shorting out on the 15-20m extended wire and how the launcher reacts to being fired on the ground.

My plan for the cannon support is to just place it in the sand leaning on the recoil support (which is a 1" x 12" tube sticking out the side, perpendicular, to the chamber). The front of the chamber will then have a sand filled bag placed under it to raise elevation to about no more than 20 degrees. More plastic bags will be filled with sand and placed over the recoil support pipe and behind the launcher.
I assume the cannon will jump and move back but hopefully this will have little effect on the projectile.

I'll have everyone stand at a 60 degree angle behind the cannon; so not directly behind but far enough around to be out of the way of any fibreglass failure.

At this stage, no attempt at tracking the projectile is being made. Magic powder is tempting but I would have to drill a hole through the sabot to allow any gases to ignite it and this may melt the sabot and cause separation issues. I was thinking of stuffing the holes in the tail of the projectile with steel wool to help ignite the magic powder on the basis of the barrel temperature being significant enough to ignite the steel wool without much direct contact with the flame front (so no drilling holes in the sabot). Keep in mind this will be carried out in summer, reasonably close to a wooded area.

Apart from that, an ATV will search roughly a kilometer section of the beach about 3.5-4.5km away from launch site. Due to time and petrol constraints, it will literally be a drive up and then back down the search area.

I know all this planning may sound overkill but in NZ we don't have many large, flat, lifeless, unoccupied areas to do launches like this comfortably and regularly. Also, my friends who will be helping me have no idea what they're doing, are impatient and will need clear instructions, I will have to plan for everything beforehand. Not to mention the fact this is potentially quite dangerous with a lot of time, effort and money invested in it.

[jackssmirkingrevenge]

The front of the chamber will then have a sand filled bag placed under it to raise elevation to about no more than 20 degrees. More plastic bags will be filled with sand and placed over the recoil support pipe and behind the launcher.

Not going for the full 50-55 degrees?

I assume the cannon will jump and move back but hopefully this will have little effect on the projectile.

The projectile should have left the barrel long before the recoil moves the launcher enough to affect it.

Apart from that, an ATV will search roughly a kilometer section of the beach about 3.5-4.5km away from launch site. Due to time and petrol constraints, it will literally be a drive up and then back down the search area.

Where do you expect the wind to be coming from? If it's from the sides I would aim around half a degree in the direction of the wind to compensate, at that range even a slight breeze is going to have a significant effect.

As to filling, I would pack it with talcum powder or similar, at least it will provide a visible trail in flight to some extent and give some indication of potential landing sites.

[MrCrowley]

Not going for the full 50-55 degrees?

'twas thinking the wind might blow it off course too much if I fired it from a large angle. It would be beneficial in the sense I could dig a hole in the sand to fit the cannon in as to give it a large firing angle but I don't want to risk the projectile drifting off in to the dunes, forest or sea. Then again, a low angle might give me a higher chance of finding it due to it staying on course more.

Where do you expect the wind to be coming from? If it's from the sides I would aim around half a degree in the direction of the wind to compensate, at that range even a slight breeze is going to have a significant effect

Think I talked about this before but can't recall what I said. Last time I was there there was a strong southerly (tail wind blowing diagonally to the ocean), I probably should expect anything though.

As to filling, I would pack it with talcum powder or similar, at least it will provide a visible trail in flight to some extent and give some indication of potential landing sites.

Perhaps red dyed talcum powder...

...better than nothing I 'spose.

[jackssmirkingrevenge]

'twas thinking the wind might blow it off course too much if I fired it from a large angle. It would be beneficial in the sense I could dig a hole in the sand to fit the cannon in as to give it a large firing angle but I don't want to risk the projectile drifting off in to the dunes, forest or sea. Then again, a low angle might give me a higher chance of finding it due to it staying on course more.

The wind is going to affect it as long as it's in flight. Seems a bit silly to have attempted to optimise everything then fire it at a much less than optimal launch angle...

Think I talked about this before but can't recall what I said. Last time I was there there was a strong southerly (tail wind blowing diagonally to the ocean), I probably should expect anything though.

Expect a moderate wind diagonally across its path to blow it at least 10-15 metres off course over a couple of kilometres.