Material Dilemma

[Moonbogg]

So, I am making this hybrid cannon and I am, yet again, battling between strength vs weight benefits. I'll keep this simple. I want some of the parts to be stronger than what aluminum can offer so I am considering a strong stainless steel for the end caps and that will put the cannon at a healthy 30+ pounds easy. Is that just too ridiculous for a hand held in your opinions?
I planned on having the cannon be held in the gatling gun orientation with two handles and having the cannon down by the hip area.

[streetfire]

you can have both strength and lightweight with carbon fibre reinforced aluminium or just carbon fibre it is kind of expensive however

[jackssmirkingrevenge]

An M60 with a 200 round belt can be fired from the hip by a healthy individual, and weighs about 35 lbs.

Is it the ideal configuration for such a launcher though? Accurate aiming isn't quite feasibly, even with a laser fitted you couldn't steady it - shouldn't it be shoulder fired? Or are you afraid to have the chamber next to your head?

[Moonbogg]

An M60 with a 200 round belt can be fired from the hip by a healthy individual, and weighs about 35 lbs.

Is it the ideal configuration for such a launcher though? Accurate aiming isn't quite feasibly, even with a laser fitted you couldn't steady it - shouldn't it be shoulder fired? Or are you afraid to have the chamber next to your head?

I don't like the idea of any chamber next to my head, especially a 4x hybrid. The strength of the cannon should be overkill and will be hydro tested to at least 600psi. Shoulder fired would be good for aiming, but I have plans to shoot heavy stuff, like soup cans and other heavy things. I think a heavy recoil with a shoulder fired cannon might be unstable to hold. A hip shooter seems better for heavy stuff, and I will have feet on the cannon for table shooting if I want to aim and might even get a little table to rest it on.
But the weight just seems like a lot for any hand held, although the BL cannons are over 26lbs and they are 1x combustions...

My venom hybrid is huge and only weighs 18lbs total, but I could get away with that due to the lower pressure. Perhaps I will design it to be held in all 3 configurations. Hip shooter, table rest shooter, and even shoulder fired if I am comfortable with it. Maybe shoulder fired at lower mixes maybe.

[MrCrowley]

I know my hybrid is about ~30lbs, last I checked it was 15kgs I think.

I can carry it about 100m before getting tired so as long as you're not running a marathon with it, the weight is fine if you're just firing from one place.

[mattyzip77]

I dont know if your a drinker, but a 30 pack must weigh close to 30 pounds, lol, figure it out!!

[jhalek90]

I wonder if anyone has uses titaniumn for a hybrid...
Might be to brittle though.

worth considering?

[warhead052]

If it ends up to heavy, might I suggest a tripod? Or skids, and make it look like a Lahti l-39?

I would recommend titanium, people use it alot, and from what I hear its very strong and sort of light.

[velocity3x]

I want some of the parts to be stronger than what aluminum can offer so I am considering a strong stainless steel......

Are you using Cosmos to determine the strength of the aluminum end caps? If so, the result could be incorrect. Cosmos has incorrect properties values (default values) for aluminum in the library. The last cannon I built was designed to an FOS of 3 kpsi. After building it, I found the default property values were incorrect. I entered the correct property values and found the actually FOS is 11.5 kpsi.

(EDIT) My Cosmos library had the tensile strength for 6061 T-6 set at 14ksi rather than the correct value of 42-45ksi. It cause me to greatly over-design. From researching machinist forums, I see that many people have been fooled by this same error.

[jackssmirkingrevenge]

What safety factor are you going for though, what discrepancy between working pressure and failure pressure would you like to achieve? I have a feeling you might be setting the bar a little high.

[Moonbogg]

6061-T6 properties are correct in cosmos. The end caps are plenty strong for pressure holding. The main issue comes in with the tie rod clamping force. The clamping force required to give me the safety margin I want is too great for the aluminum to handle with an adequate safety factor. Also, the design requires tapping into the front end cap to hold the piston housing. I don't want to tap into the aluminum since those screws might have to come out for piston servicing and tweaking. Aluminum threads strip and they are not strong enough for a high strength bolt let along frequent reuse.

I am going for an all around safety factor of around 6-8, with the exception of the tie rod "preload". The tie rods will be able to hold about 4.5 times the pressure they will encounter for regular use and 3 times for the hydro test. A common preload safety margin is 2.5 and I just wanted more for this and aluminum end caps can only handle that pre load with a safety margin of around 2. Thats only in one direction on the end caps. So now, you have the end caps stressed from the tie rods and all of a sudden you slam them with the combustion pressure from the other direction. I am not comfortable with this.

17-4ph end caps fix the strength issue, they are more ductile, and they can be tapped into easily, simplifying the design. The only issue is a little extra weight.

So yes JSR, I may be aiming pretty high for the safety margin here, but when I use this thing, and especially when I hand it to a friend to fire, I want to know that this thing is total overkill strength wise and the thought of it failing should make me laugh due to that being really unlikely.

[Brian the brain]

My Cannon for the demo I did at the Chunkin event in Belgium last year was a good 20 kg.
A bit too heavy to really carry it around much.

But the reason for all that weight was safety.
A PVC launcher could be shot at the same pressures I used there and at the same dimensions it would have weighed 25% of the metal version.

I did not want anything to happen with 5000 people watching....

Well, not just me...

For safety reasons they forbid me to use pressure rated PVC..

[jhalek90]

I stil think titaniumn will be worth looking into.
Very strong, and depending on the alloy, lighter than aluminum.

Edit: also it TIG welds very well.

[Moonbogg]

I stil think titaniumn will be worth looking into.
Very strong, and depending on the alloy, lighter than aluminum.

Edit: also it TIG welds very well.

The cannon would cost 10 grand.

[mattyzip77]

I stil think titaniumn will be worth looking into.
Very strong, and depending on the alloy, lighter than aluminum.

Edit: also it TIG welds very well.

The cannon would cost 10 grand.

Moonbogg you got the big bucks, who you kiddin, lol!!