I'm only leaving the rest of this unchanged for historical and reference purposes.
This should give you the gist of the design:
The holes are 5/16" diameter x 3/8" to 1/2" deep. The foam is the 13mm (~1/2"-ish) pink stuff that I ordered from china
The filling is silicone rubber, either the sealant type that cures with contact to moist air, or the mixed type that cures anaerobically.
The tip is 1/2" mcmaster adhesive felts with the adhesive ripped off.
Length is 32mm-36mm
Works in a conventional pvc-wye hoppers
Safer than any other hopperable darts that I know of
Comparable performance to slugs
0.8g +-.1g @ 2 sigma
Captain Slug, for putting felt bumpers on his darts and being the first person I know of to make ANY effort to pad ammo
Ryan McNumbers, for being helpful and supportive with pretty much every dart making scheme I've had.
Most of all Caffeine, for telling me that brad pointed drill bits can make good holes in foam, AND for suggesting silicone adhesive as a dart-tip material. He suggested these things to me shortly before he died a couple years ago. Efforts to resurrect him have proven futile, but I haven't give up.
The details are as follows:
Make non-adhesive, 1/2" felt pad. Die cutting non-adhesive foam is the best solution here, but I didn't (and don't) have that. So, I tore the adhesive off of some of the sticky felts that are used normally for metal weighted slugs*.
Aquire a 5/16" brad-pointed bit with a stop, and some sort of jig to guide the dart into the center of the blank. My jig was made from 5/8" x ~1/2" PEX, 1/2" x ~3/8" PEX, and 11/32" x ~5/16" brass tubing.
The outermost PEX (white) holds the dart, while the brass guides the drill.
The duct tape acts as an endstop that determines the depth of the hole
Put your blank in something to hold it while the silicone sets. This jig was precision made to do things other than this--All you need is a board of something with 1/2" holes in it to hold the foam without damaging it, position doesnt matter.
I used a 1 to 1 mixed silicone RTV at first for this, but I think for most people silicone sealant is more practical and less messy. I've used both general purpose sealant, and a low-viscosity variant (Dow Corning 734). The low viscosity variant seems to bond better with both felt and foam, but the general purpose is MUCH more controllable and less messy.
It helps to get the nozzle in the hole to reduce trapped air and better bond with the foam.
Add the 1/2" diameter felt pad
For not-a-writeup, these would be done in greater numbers than 1, but beware that the silicone forms a skin fairly quickly that will prevent the felt from sticking. I would estimate this takes 5-10 minutes, which for me was filling 30-40 darts before needing to switch to felt placement. Also beware that this type of silicone requires about 24 hours to set enough to be removed, and at least 1 week to set enough to use. During this time [internet chemist hat], the sealant cures by expelling acetate ions into the moisture in the air, forming vinegar and it's familiar caustic odor. It needs to do this a lot to cure, so it cannot be kept sealed away during the cure process, as this would saturate the air with vinegar, reaching an equilibrium with the silicone that prevents curing.
The low viscosity silicone sealant may turn out to be necessary to adhere the foam to the silicone. I don't have any real-use testing with these, but the general purpose sealant darts were very east to pull apart, separating foam from silicone. Low viscosity silicone sealant is MUCH messier, on account of not flowing controllably from the caulk gun, and also on account of not being able to bulge as much without spilling out of the dart.
Especially with mixed silicone and low-viscosity silicone, these darts are quite difficult to make well, and there are a wide variety of ways they can be flawed, resulting in a wide variety of symptoms**. However, if these type of materials are used with this basic method, no lack of quality can present as serious a safety hazard in the way that stefans and damaged / poorly made slugs can, since nothing hard is in the dart. You still, of course, don't want to get hit in the eye-Goggles, people!
*There are many ways to do this, and difficulty seems to vary from roll to roll. I ended up needing to stick the felts together, then rip the felt off the central adhesive blob one at a time with a roll of white felt for these. There are a variety of ways to do this, the best one depends on the roll of felt. In any case, I need to find a source for 1/2" non-adhesive felt pads.
**More coming on that
Great job on these, especially since they're hopperable without any wye modification. How heavy are they?
0.7g-0.9g, for the most part 0.8g. The variation in weight is mostly from the hole depth
I remember one of your design goals with the rubber-headed darts was better aerodynamic performance than slugs. Did that goal go by the wayside to meet the hopper requirement, or are these a separate evolutionary line of darts?
A bit of both. Making special hoppers for rubber tipped darts is still of-interest, but I'd also want to have vented hollow domes for better padding, and the special hoppers need to be extremely low cost/labor (at least for me) to be widely adopted. These less than revolutionary VANS work with the hoppers people already have, which are cheap and easily implemented. Since I'd like to be mass producing darts by early summer, I'll take care of these first. This method also allows me to advocate these metal free darts without directly telling them to buy MY metal free darts, so I can be a safety nazi more effectively. If I had a supplier / method for domed felts....
Do you think it would be possible to burn the hole instead of drill it?
Generally no. The silicone needs the rough surface of the drilled foam to bond.
I don't understand; why do you have to remove the adhesive? Wouldn't that help it bond to the silicone better?
Silicone is basically immune to adhesives. By using bare felt, the silicone seeps in between the threads and cures, forming a bond.
Would a 1/4" drill bit work for this? Due to the slightly smaller diameter, I suppose you'd have to drill deeper to hold the same ammount of silicone. Also, do you have an McM number for the silicone you used?
A 1/4" drill isn't completely out of the question, and would make cleaner holes with fewer rejects. But to get the same weight, you need to drill 56% deeper, or close to 3/4". At some point, the front-heavy balance of the dart will be sufficiently disturbed that the darts will no longer fly straight. So really, the 1/4" holes are only good for lighter darts / lower powered blasters.
75825A2 for the low viscosity stuff that bonds well to the rough foam. The general purpose stuff I just got at a hardware store.
Edited by KaneTheMediocre, 27 November 2012 - 04:18 AM.