SpudFiles

Mr.michael.2468 wrote:now i look at my 1/2in barreled sniper cannon with a sigh...

You can still do it with a 1/2" cannon, it's two different approaches to the same problem.

Let's take a couple of anti-materiel rifles as an example.

The Polish Wz. 35 could throw a 7.92mm round well past 4,000 feet per second. It did this by using a massive cartridge in a full bore barrel:



The Barret M82 has a bore almost double the size at 12.7mm, and is capable of throwing a similarly sized bullet to the one the 7.92mm Wz. 35, at roughly the same velocity, using the saboted M903 round.



You can get high performance with full bore barrels, but using larger barrels and sabots allows you to work with lower pressures and slower valves and get the same if not better performance.

I'm really keen to do some long distance (1500m+) range testing. I'm hoping you guys will talk among yourselves, come up with a cheap, easy to make, aerodynamic, suitable design for me and then I'll test it out. I cbf doing all the hard work!

MrCrowley wrote:come up with a cheap, easy to make, aerodynamic, suitable design for me

Here you go

Obviously you're not aware how aerodynamic kiwi's are without fins in their ass

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To be honest, I expected something with a sheep

MrCrowley wrote:Obviously you're not aware how aerodynamic kiwi's are without fins in their ass

Ah, but it has a hammer and nails in its ass, for added sectional density!

Cute little vid, shame the kiwi is so disturbingly flesh coloured...

To be honest, I expected something with a sheep

Not pointy enough, though admittedly ready for tuft testing

Seems like a bit of hassle to get the right C.G. for a Sears-Haack body to stop it tumbling, as well as the right diameter, length and materials. No idea how I would go about making one. I think something that'd be easy would be like a 30mm mortar shell, don't they (full-sized mortar shells) have a C.D. of like 0.04?

Wonder how much it'd cost to get made...

MrCrowley wrote:Seems like a bit of hassle to get the right C.G. for a Sears-Haack body to stop it tumbling, as well as the right diameter, length and materials. No idea how I would go about making one. I think something that'd be easy would be like a 30mm mortar shell, don't they (full-sized mortar shells) have a C_D of like 0.04?

Most mortar shells seem to have a C_D of around 0.1, but even if you had one made it still wouldn't address the issue of sectional density. If it was a full bore round, you could either have it light enough to be shot fast but with very poor sectional density, or vice versa.

That's the beauty of discarding sabots, they provide low density in the barrel, which is what you want for a fast shot, but high density outside the barrel, giving much better velocity retention.

This is how I envisage it being built - tube body, with a weighted nose section, a lightweight tail and fins made of thin blasa, ply or aluminium with low area but large contact with the barrel (hence the cutouts) to keep the projectile centred. This allows the use of a simple one-piece cylindrical sabot that doesn't need complex interlocking petals.

Care should be given to detail such as tapering the edges of the fins as these make a significant difference to C_D, as well as sanding down any beads of adhesive where the fins are attached etc.

What part of the drawing are the fins, sorry?

To have enough weight I'm thinking of using 20mm PVC and possibly thin sheet metal (tin?) for fins. Say the dart is 200mm long, would you make the fins something like 80mm long and perhaps 20mm tall? I'll figure something out for the nose but it'd probably have a fishing sinker or two in the front and perhaps another two in the PVC tube where it attaches. Epoxy/filler would be used to smooth the exterior gap between the PVC pipe and nose.

MrCrowley wrote:What part of the drawing are the fins, sorry?

The white parts, suspended by magnets on rectangles of creamy goodness

Attaching the tin might be a bit tricky, you might need to slot them together and into grooves in the pipe in the same way a throwing dart is manufactured.

Attaching the tin might be a bit tricky, you might need to slot them together and into grooves in the pipe in the same way a throwing dart is manufactured.

Great minds...

MrCrowley wrote:Great minds...

... make quick and dirty paint drawings

Clever bastard!

Perhaps I can find someone with a scroll/band saw. I don't trust my handsaw skills to cut down the length of PVC like that. I've tried before and once you've made one cut (essentially cutting it in 'half'), trying to make the 'quarter cut' is very difficult since the PVC flexes too much. Guess I could use aluminium if I could find some.

the dart thing gave me an idea, i took an aluminium dart flight holder thingy and cut of the threads, took the dart flight and cut it down, then took a bullet and glued it to the back, hope it works and sorry for the sh*t picture but i used my phone

i was looking around but couldn't find any diagram of the CheyTach m200 Intervention, manly the round it fires. i know its a .408 and is really really pointy

i tryd to quick scope in real life with my bros 22-250 and yea don't try it hurts your shoulder real bad, that was with a small cal to.

-_- wrote:i know its a .408 and is really really pointy

So it is... but it leaves the muzzle at almost 3,000 feet per second, and is still supersonic at 2000 yards, so not really relevant to spudguns which are mostly subsonic.

ilovefire, looking forward to your results

Just a thought on fins, how about making them from paper and impregnating them with epoxy...