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Ammo frustration

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Ammo frustration

Unread postAuthor: skyjive » Tue Sep 09, 2008 11:19 am

So after much experimentation and thinking I am completely unable to come up with a workable projectile for accurate long-range shooting. I am well aware of the principles of forward COM and rearward COP but I can't seem to get a completely stable bullet that will just go in a straight line no questions asked when I shoot at a target say 75m away. The best results have come from spherical or cylindrical ammo that is not stable but still goes sorta straight anyway, but I think I can do better. I'm sure that many of you out there have come up with very good target ammo and I would appreciate any help.
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Unread postAuthor: ALIHISGREAT » Tue Sep 09, 2008 11:24 am

hop up on a spherical projectile to make sure it shoots consistently (also increases range)?
maybe hop up on a golfball would be pretty accurate?
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Unread postAuthor: jimmy101 » Tue Sep 09, 2008 11:43 am

Do you know if the problem is the projectile in flight or the projectile leaving the barrel?

How a projectile leaves the barrel has a huge affect on the accuracy. Real rifle barrels are crowned to insure the shell leaves the barrel consistently and the blowby during muzzle exit doesn't give the shell a kick in a random direction.

Small changes in launch energy will also affect accuracy. Are you getting vertical dispersion (suggesting changes in muzzle energy) or vertical and horizontal dispersion (suggesting a problem with how the ammo leaves the barrel or instability in flight).
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Unread postAuthor: skyjive » Tue Sep 09, 2008 1:08 pm

I don't think the problem is with the shot leaving the barrel, the problem is that once the projectile is in flight it does not stay oriented toward the target and tumbles or "corkscrews" in flight. This is because I use projectiles with forward COM and drag-inducing tails (e.g. darts) to try to get them to be more accurate than spherical projectiles. However, I guess my designs aren't good enough because they are never completely stable. Also, I am using SCH40 1/2" PVC so my ammo is fairly small (and golfballs are out).
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Unread postAuthor: Gippeto » Tue Sep 09, 2008 1:34 pm

I have not worked with 1/2" pvc, how rigid is it?

Is it possible that during recoil, the barrel is "whipping" and transferring this motion to your projectiles?
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Unread postAuthor: skyjive » Tue Sep 09, 2008 1:44 pm

Its actually quite flexible, but the barrel is held onto the the chamber (which is 1" and quite rigid) by PVC rings, one of which is only a few inches from the muzzle, so I doubt that barrel whipping has a significant effect. I also have the same problems when firing from a 1/2" copper gun, which further supports the supposition that the barrel material is not the issue.
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Unread postAuthor: SpudFarm » Tue Sep 09, 2008 3:12 pm

well
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Unread postAuthor: skyjive » Wed Sep 10, 2008 10:59 pm

I assume you use a sabot with that bad boy?
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Unread postAuthor: CasinoVanart » Thu Sep 11, 2008 1:40 am

skyjive wrote:I assume you use a sabot with that bad boy?


And here i was thinking that Spudfarm had a cross shaped barrel. :roll:
Of course he uses a sabot :D

Actually Spudfarm is so good he can even make angled shots with that dart! :P
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Unread postAuthor: cannon monkey » Thu Sep 11, 2008 9:09 am

ok lets see how this goes (loltms) but any ways i been brain dead in the past week and i need cheap easy items to get my hands on or to make cheap
for my 2 inch pvc barrel i been shooting water balloons just for fun. with McDonald water cup (they can stand to 90 psi with out ripping)
but i want new things to shoot i am low on money and cant use potato's or apples or any food at all something reuse able
does any one have any ideas??????

i sorry if i posted this in the wrong place :) thanks
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Unread postAuthor: DYI » Thu Sep 11, 2008 7:34 pm

This is the most stable/effective round I've been able to make with simple household tools and materials:

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Please note that this design is not suitable for hybrids, due to its extensive use of tape. Using a wooden plug behind it, this 50mm round worked fine at 500psi.
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Unread postAuthor: cannon monkey » Fri Sep 12, 2008 11:04 am

lol ya that dart spike think kinda toooo dangerous for where i live but thanks any ways XD
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Unread postAuthor: skyjive » Fri Sep 12, 2008 2:00 pm

I'm a little unclear on what the sabot is made of, is it a wrapped cylinder of duct tape cut in half or something? The inner part is obviously a pipe segment. And what are the relative masses of sabot and projectile? Duct tape in that quantity is very heavy, so aren't you wasting a good bit of energy accelerating it? Apart from that, looks pretty fearsome.
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Unread postAuthor: DYI » Fri Sep 12, 2008 7:55 pm

I'm a little unclear on what the sabot is made of, is it a wrapped cylinder of duct tape cut in half or something? The inner part is obviously a pipe segment. And what are the relative masses of sabot and projectile? Duct tape in that quantity is very heavy, so aren't you wasting a good bit of energy accelerating it? Apart from that, looks pretty fearsome.


Yeah, the tape does waste a lot of energy - I could only get this design up to about 600-700 fps out of the SCTBDC at full power. However, as I said, it's with basic tools and materials. With a lathe, and access to some strong, lightweight plastic bar stock, your range of options is much larger. This dart worked well in terms of accuracy, stability, and sabot separation, but it wasn't hardened, and could be stopped by 6mm steel plate.
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