High precision nail darts?

[FighterAce]

I've found that my darts dont hit the same spot every time. Each one has its own flight characteristics.
I'm looking for a dart design that could hit the same exact spot over and over again with a gun thats fixed to a stationary object. I know smoothbore has its limitations but I think I could melt spiral grooves in my pvc barrel with a heated hexagonal nut and then just sand the inside to achieve a rifled barrel. I'm just not sure for the bullet design.
So far I've tried my darts with a longer tail, fins, wooden dowels, hot glue and that water hose tail but nothing is accurate enough.

Any ideas?

[Forum Admin]

Get a scale that is accurate to about .01 grams. Sort your nails by weight. Then find a consistent way to make tails. Be sure the tails are centered. Then weigh the completed darts and be sure they weigh within a grain or two of each other. (sorry for the change in units  ) If you do those things, you will tighten up your groups. Another thing is to be sure the blast from firing does not move the stabilizing tail.

[BoyntonStu]

I've found that my darts dont hit the same spot every time. Each one has its own flight characteristics.
I'm looking for a dart design that could hit the same exact spot over and over again with a gun thats fixed to a stationary object. I know smoothbore has its limitations but I think I could melt spiral grooves in my pvc barrel with a heated hexagonal nut and then just sand the inside to achieve a rifled barrel. I'm just not sure for the bullet design.
So far I've tried my darts with a longer tail, fins, wooden dowels, hot glue and that water hose tail but nothing is accurate enough.

Any ideas?

You have stayed the accuracy goal as I see it.  Very ambitious.

Gary Barnes achieved this accuracy with his smooth bore:

http://www.glbarnes.com/accuracy.html

Unbelieveable!!


Look at his guns (and prices).

[FighterAce]

Get a scale that is accurate to about .01 grams. Sort your nails by weight. Then find a consistent way to make tails. Be sure the tails are centered. Then weigh the completed darts and be sure they weigh within a grain or two of each other. (sorry for the change in units  ) If you do those things, you will tighten up your groups. Another thing is to be sure the blast from firing does not move the stabilizing tail.

The water hose technique is very consistent but the problem seems to be its weight. I think a digital scale will squeeze into my budget in a few weeks so I can confirm that.
I dont think the blast from firing moves the dart at all cause its got no recoil, bipod + my steady hand 

Its not ambitious at all. I'm already getting less then 2cm groups out of my M4 setup. The problem is keeping that.
When I shoot from my balcony at a downward angle I can get insanely tight groups but when I get down and shoot level at a target, the darts end up all over the place. I'm not quite sure whats the cause of this...

Here take a look... this one is from the balcony


and level..


Sry, I had to angle the camera so I can get the whole target

[FighterAce]

Last night I was playing around with different paper tail designs and found that short tails fly pretty nice. I made a few and shot a test group this morning.



The tailless nails are from previous shots

They are better then the regular darts but they dont seem to hit level with the muzzle. I made a few with slightly longer tails. The glue is drying right now so I'll have to wait a bit to test them out.

[FighterAce]

Found the problem... Took me awhile to remember that the nail is not centered to the barrel and that I'd need a discarding sabot to make it level in the barrel thus making the nails fly straight. When I shoot at a downward angle, the nail centers itself in relation to the barrel and flies very accurately. Time to recall some papercraft skills and make an easy to make paper sabot 

[Forum Admin]

That makes a lot of sense. The cork tails that Stu uses do a remarkable job of keeping the nail centered, as do the hot glue rings and shotgun wads. Judging from your website's section on papercraft, you will be able to do the same thing with paper. If you can find a easy way to make a discarding sabot, you can use smaller diameter stabilizers that minimize drag, while still retaining the power benefits of a larger bore. 

[FighterAce]

I hope I wont need to make sabots... I know it would be a lot of work for something thats just gonna fly out and be useless. I'm still looking for that magical 12mm rubber/synthetic tubing. It would be a nice replacement for the corks, wooden dowels and paper...

[FighterAce]

I've tested those bigger darts this morning. They flew pretty much level without tumbling. They are 1/2 the size of my regular darts and their accuracy is at least 3 times better. I'm very happy with this design  I'm gonna make some more to check their flight at longer distances but so far they seem to be a very good candidate for a good bullet thats fast and easy to make.

Here it is... 5cm group at 10 meters 


Back side

[Forum Admin]

That's some good grouping. Looks like you are getting somewhere. 

[FighterAce]

A little update... I made a master template for those shorter tails. From that I've made 10 new ones. I used a sheet of A4, 200 g/m² paper. Its like a perfect middle of paper and cardboard. I used non-diluted wood glue to hold the nails in place. The whole inside of the paper tail is also coated in wood glue. To me it seems like I got a pretty consistent shape. Not sure about the weight tough...
I found that on some darts, the nails werent centered to the tail because they were bent. A few mins ago I found the solution... rotate the nail inside the tail until it lines up.



I'm gonna shoot all of them tomorrow morning to check grouping...

btw. I use a bolt system in witch the barrel moves back and forth and it rotates to lock. When I insert the dart, the nail tip rests at 6 o'clock .- in relation to the ground. When I rotate and lock the barrel, the nail tip shifts to 4 o'clock position.
Due to movement and shock felt on the bolt between loading and firing the dart keeps shifting orientation inside the barrel. A light tap on the bottom of the gun will bring back the nail tip back to 6 o'clock position just before firing. I'm hoping this knowledge will also improve my grouping because the dart will always be in the same position inside the barrel. This could sort of replace sabots dont you think?

[Forum Admin]

Making sure the dart is in the same position in the barrel each time you shoot should help improve your grouping. Looking forward to seeing your shots.

[FighterAce]

I shot just 4 so I can zero to the rest but that didnt work out very well... The shots are outside the adjustment range of the red dot. I'll have to raise and turn one side of the picatinny rail to compensate but I dont have any tape left to do so.
Here are the test shots...



Man I really gotta replace that target, its full of holes 

[Forum Admin]

Looking better, that some pretty good grouping. How far away are you shooting from?

[FighterAce]

Looking better, that some pretty good grouping. How far away are you shooting from?

darn.. sry I didnt even see your reply  I think it was somewhere between 10 and 12 meters

Yesterday I noticed that my regular paper darts fold easily at the point where the nail head meets the paper. I think this is one of the bigger causes of inaccuracy and tumbling. Today I picked up some 200 g/m² A4 paper and I'm making a small batch of my regular design nail darts. They are a bit shorter because I had to optimize the size so I can use up the whole sheet of paper cause all that thickness doesnt come cheap especially on the large scale.
Also, I'm gonna try the 16d nails and see how they perform. I'm hoping the longer nail body will make the dart more stable.

btw. I think I got an idea to replace the sabots but no ammo to try it on... I spent all my darts and I'm not making any cause I'm not sure what to make right now, still experimenting with different designs