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Handheld/recoil

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Handheld/recoil

Unread postAuthor: SpudFarm » Tue Jul 27, 2010 4:24 am

Hello, I am looking to build a piston hybrid for my next project when I have gotten my other hybrid to 20x.

It will be made with a 12.5cm ID by 40cm long chamber and have something like a 2m long 2" barrel.

The first HGDT run told me around 8000joules, sounds kind of high to fire from your shoulder to me. Do you think it can be done?

The cannon will probably end up being 50-80 pounds in total.

Thanks!
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Re: Handheld/recoil

Unread postAuthor: jackssmirkingrevenge » Tue Jul 27, 2010 4:40 am

SpudFarm wrote:The first HGDT run told me around 8000 joules, sounds kind of high to fire from your shoulder to me. Do you think it can be done?


A 50 calibre anti-material rifle does over twice that, and they can certainly be fired from the shoulder.

I would still want an effective muzzle brake though, as well as having the barrel and breech free to recoil on the stock supported by a spring/hydraulic buffer as in the NTW-20:

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Unread postAuthor: inonickname » Tue Jul 27, 2010 5:10 am

A 50 calibre anti-material rifle does over twice that, and they can certainly be fired from the shoulder.


Yeh, easily in regards to the recoil..but the weight, not easy. 80 Pounds from the shoulder?

[youtube]http://www.youtube.com/watch?v=yiWn-0gKOm8[/youtube]

That weighs less than 30 pounds. Don't expect to be able to shoulder and aim it accurately for long.
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Re: Handheld/recoil

Unread postAuthor: Ragnarok » Tue Jul 27, 2010 5:17 am

SpudFarm wrote:The first HGDT run told me around 8000joules, sounds kind of high to fire from your shoulder to me.

The muzzle energy is not the important bit. The momentum (including that of the propellant gasses) and mass of the launcher is what defines recoil - ultimately defined as recoil energy of the launcher.

With a 50+ lb cannon, then you could absorb quite a lot of recoil - however, I wouldn't really be prepared to call it "safe" unless I knew enough to figure some calculations. (i.e. projectile mass and associated velocity, chamber size & pressure, and specific launcher mass - some of which I know you've listed, but I'm still pointing them out as important.)
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 27, 2010 5:59 am

As Rag says, momentum is the revelant parameter.

A 50 cal rifle firing a 50 gram projectile at 800 m/s would generate 40.0Ns of recoil.

A hybrid firing a 100 gram projectile at 565 m/s would have same muzzle energy as the above, but generate 56.5Ns of recoil.

A recoil system is definitely in order ;)
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Unread postAuthor: CpTn_lAw » Tue Jul 27, 2010 7:12 am

I remember talking with Spudinator a few yars ago, about his shoulder fired hybrid. He used to shot frozen apples, and said that he usually would be able to shoot it twice a day, not more, because two shots would bruise his shoulder.
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Unread postAuthor: Ragnarok » Tue Jul 27, 2010 7:41 am

johnssmokingrefridgerator wrote:A recoil system is definitely in order

Well, it's important to be clear about what a recoil system can actually do. Improvements can make it easier to handle recoil, but other than actually reducing the momentum of projectile/gasses or increasing launcher mass, you don't actually reduce recoil energy. Laws of motion.

What you can do beyond that is soften but lengthen the recoil - turning it into a "push" rather than a "kick", which means its perceived as less violent.
Basically, you still have to catch/stop the launcher, but it can stop it actually injuring you. The right system could quite easily have solved Spudinator's bruising problems.

Now, one of the best pieces of advice I have heard for shooting high recoil rifles is to keep your weight towards the front foot, grasp the stock with your front hand pushing away from you, then pull the rifle firmly back into your shoulder with your other hand.
This means you've got a solid "join" between you and the rifle when you fire, meaning you act much more like part of the recoiling mass, and because it's already pressed hard into the shoulder the rifle can't "hit" you.

It's not a great stance for accuracy, but then again, it stops you flinching horribly and missing entirely. I've seen videos of people absorbing 200+ ft-lbs of recoil energy with that kind of method, so it's pretty effective.

EDIT: One warning. Do NOT use any kind of muzzle brake unless you've got really good hearing protection. They dramatically increase the sound pressure level for the shooter - can potentially cause permanent damage even with typical protection.
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Unread postAuthor: SpudFarm » Tue Jul 27, 2010 11:42 am

I will look what I can do for the muzzlebrake Jack. I have allways wanted to have one on my hybrid but it is not put to use when the cannon is fixated to a floor.
Do you have ideas for a muzzlebreak that doesn't jam up ammo that fails such as a APFSDS round loosing it's sabot? Many tiny holes is possible but hugely time consuming and probably not so effective.
Something designed around a 2" pipe nipple would be usefull if I want to remove it and add a silencer instead.
I imagine a nipple with square steel tubed welded on in a backwards facing angle, probably a pretty big one to make much difference at such low pressures.

I did know that many rifles has more then 8kj but that is the energy with a 280g slug and 5x so it might simply push me over.

Ragnarok, I haven't started designing this at all yet. I just want to know if it can be fired without super-human powers before I start designing.
The ammo weight and associated velocity is hard to determine since I will be firing all sorts of stuff.

A recoil system can probably be made easily using snowmobile shocks without a spring. They behave great under those conditions.

As to the weight, I think I can handle it if I distribute the weight evenly. I might have to strap it around my back if it turns out to heavy.

I am used to firing rifles and other sort of guns, but as ragnarok pointed out: There is a huge difference in how the recoil is transferred to the shooter. It should not kick much at all. I am worried that I end up failing to sholder fire it and have one more "useless" launcher.
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Unread postAuthor: Ragnarok » Tue Jul 27, 2010 12:48 pm

SpudFarm wrote:The ammo weight and associated velocity is hard to determine since I will be firing all sorts of stuff.

Well then, it's clearly going to recoil differently with different projectiles.

However, as you've now theoretically given enough information for a rough estimate...

Momentum of Gasses for 5x 12.5cm ID 40cm long chamber + 280g apple at 240 m/s (~8000 Joules ME) = ~100 Ns

Recoil energy in 50 lb launcher = ~220 Joules
Recoil energy in 80 lb launcher = ~135 Joules

Compare to the Barrett M82, which is about 135 Joules without the muzzle brake. Depending on efficiency of the brake, that might halve (so, ~70 joules with a good muzzle brake). Bear in mind however, that the efficiency of launcher and firearm muzzle brakes will be different.

You can theoretically withstand 220 Joules recoil , but it would demand you did the right things - get your recoil technique wrong and you run the risk of ending up severely injured.

For reference, 220J is about what you'd get from .700 Nitro Express in an 18 pound rifle. You can see how to get it right with .700 NE here.
If you want to see what happens if you get it wrong, you can see someone messing up with the the similar recoil .577 T-rex round here. (However, you can certainly get it much worse than that. Broken bones are possible.)

Recoil systems might give you more leeway in what you get wrong, but there's only some mistakes they'll allow for.
More mass is the only way to actually scrub off recoil energy, but even a 50 lb. launcher will be pretty heavy.
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Unread postAuthor: SpudBlaster15 » Tue Jul 27, 2010 1:08 pm

I think the sheer weight of the launcher will be more of an issue than the recoil energy. At 80lbs, the launcher mass will absorb a very significant fraction of the potential recoil energy, but it will make aiming and balancing nearly impossible.

My hybrid weighs in at only 30lbs, and although the mass doesn't pose an issue for shooting, it's bordering on what is practical for a hand held, shoulder fired launcher. Honestly, I can't see how you'll be able to manage something that weighs ~3 times greater.
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 27, 2010 1:11 pm

SpudFarm wrote:Do you have ideas for a muzzlebrake that doesn't jam up ammo that fails such as a APFSDS round loosing it's sabot? Many tiny holes is possible but hugely time consuming and probably not so effective.


Technically, a large suppressor would also act as a muzzle brake. If you want to fire saboted rounds, lots of small holes will be time consuming but probably the safest bet in the case of sub-calibre rounds.

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Unread postAuthor: SpudFarm » Tue Jul 27, 2010 11:41 pm

Ragnarok: I would think it could be possible to make a plate for the "butt" of the cannon that matches my body to disperse the energy over a larger area. That would seriously limit the broken bones hazzard.
And, as I plan to take this gun to 10x depending on how it turns out to behave when fired, it might be needed.
(I said 5x because that is the lowest mix I am prepared to accept)

Spudblaster: I can make it with straps that supports it's weight on my neck, then have some "butt" assembly on the middle of the cannon so it can be aimed pretty easily once I get it up from the ground.
If it turn's out to be to heavy, it's possible to just make two handles on it and fire it from the hip with a laser sight.

But if it turn's out to be heavy for that to, it would be pretty cool to mount it in some AA gun simmilar setup with wheels for transport.
I couldn't find a picture of exactly what I mean but I am talking about those who take use of a standing shooter behind it and recoild to both his shoulders.
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Jsr: I guess I could just make a big suppressor with a muzzle brake inside to. And I have been thinking a bit about it, mabe grooves going along the length of the barrel will be more effective then holes? It will be simpler and it will be hard to jam something in 3mm wide grooves.
This is what I am talking about, but with much thinner grooves.
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 28, 2010 12:13 am

Grooves sound... well, groovy :) and you could combine it with a simple tee brake, like the AW50 but slipping over the grooved part if you know what I mean:

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Unread postAuthor: SpudFarm » Wed Jul 28, 2010 3:10 am

Lol JSR! :D
I mean that I can make such grooves in the last 40cm or so of the barrel, then have sevral backfacing pipes welded on over the grooves.

Search for "Golf ball cannon montage" on youtobe and see if you find the complication of solid propellant powered cannon. At 3:40 in the video he shows a picture of a muzzlebrake much like I am thinking of.
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Unread postAuthor: Ragnarok » Wed Jul 28, 2010 6:20 am

SpudFarm wrote:And, as I plan to take this gun to 10x depending on how it turns out to behave when fired, it might be needed.

Well, with that 280g slug and approximated 10x performance, recoil in a 50lb. launcher will be ~550 J. It'll be ~345 J with an 80 lb. launcher.

I have seen recoil systems which can make that kind of recoil within human limits, but I'd probably still steer clear.

~~~~~

On the muzzle brake issue, I'd sooner recommend a suppressor. It should help reduce recoil (partly because of the added weight), but without the risk of hearing loss associated with muzzle brakes.

I would also point out that bruises, sprains and even broken bones can heal. Lost hearing will not.
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