userjjb

Hey guys, been awhile since I've been on NerfHaven. Looks like there's been lots of cool stuff done since last I was here! I got reeled in by the allure of the greater power of potato cannons and Nerf fell by the wayside, but now that I'm in an apartment there isn't much room for 900 fps golfballs anymore. Classes don't start for me for another week and I've been bored looking for a project to work on that will get along with my smaller confines.

Having looked at some of the stuff CaptainSlug has been working on gave me a couple ideas for a very simple semi and/or full auto nerf gun. Essentially it's a fusion of a small piston-valved pneumatic launcher along with a bolt-action breech. The key feature in this design is that the bolt is actuated by the piston, enabling semi and full auto fire.

For an example of the type of bolt-action breech I'll be using check out Retiate's Clipped AT2K.

For several examples of barrel-sealing piston-valved pneumatic launchers, see my archived thread on Spudtech. (The third launcher down uses the same size components to be used in my nerf gun)

For an example of the HPA source/setup I'll be using see CaptainSlug's Paintball Tanks With Nerf, Fun with HPA topic.

Now that that's all out of the way, here's my design:

There's a few key elements that are omitted/not obvious; In the first diagram the actual magazine reciever and clip are omitted for simplicity. Also it looks like the bolt is coming out where the darts would enter, this is just poor artistry on my part, the bolt would exit through a slot in the 1/2" PVC (see Retiate's write up to see what I mean). Also all of the breech elements are nested. Going outward to inward: 1/2' PVC, 19/32" brass, 9/16" brass, internal breech action. Finally, in the second diagram the far end of the first diagram is pictured (both 3/4" female adapters are the same part). Obviously things aren't perfectly to scale as well.

The cycle proceeds as such:
1. Dart chambered, bolt forward, breech closed, spring extended, piston forward and in contact with internal bolt action, chamber and pilot pressurized, air source open, exhaust closed.

2. Air source closed, exhaust open. The pilot vents to atmosphere and pulls the piston back. This now vents the chamber into the barrel firing the dart.

3. Spring return on bolt retracts and opens breech. Next dart enters breech.

4.Exhaust closed, air source open, pilot fills pushing piston forawrd and sealing. Piston pushes internal bolt action forward closing breech and stretching return spring. Chamber and pilot are now fully pressurized.

And the cycle is back where it started.

The wonderfull thing about this design is I can adjust barrel length and chamber pressure to customize dart range. I picked as an example a chamber 12 ci @ 30 psi, with a 12 in barrel. One of the members on Spudtech developed a tool that simulates the performance of a gas gun given various parameters and outputs expected muzzle velocity, valve cycling etc. The tool is called GGDT and is available for download at the author's website if you guys would like to try it out. Here is a screenshot of GGDT with the info for this gun input:

You can see from the graph that the dart will exit the barrel 20 ms after firing. I expect the spring to take significantly longer than this to open the breech, so there shouldn't be any gas excaping even though firing and breech opening occur "simultaneously".

The air source on the 3 way solenoid will be normally open and the exhaust normally closed. So by merely pulling the trigger (and thus cycling the valves) the gun will fire and reload, semi-auto. Here's an example of the 3 way solenoid I plan to use. Alternatively the clip could be taken off and dart's loaded manually in semi-auto mode if the user is out of loaded clips.

Alternatively, the ball valve leading to the pop-off valve can be opened. Now once the pilot reaches the pop-off pressure the valve will open and actuate the piston valve. After firing the continued air source feed will reseat the piston valve until pop-off pressure is reached again, full-auto. For an example of a full-auto piston valve launcher see markfh11q's website.

The best thing about this launcher is that it requires at most a dremel (although you could get away with hand tools) and no machining. All parts are readily available at Home Depot (and wherever you get your brass), with the exception of the the HPA setup and the 3 way solenoid valve, which is around $20 (less if you buy one surplus off Ebay). You can even leave out the o-ring and check valve on the piston, it just improves performance, although o-rings are easy to get at Home Depot and you can make your own check valves for about 90 cents (if anyone is interested I can make a write-up on how I make mine). Once built the whole thing can be dismantled for servicing and repair with no tools whatsoever. Also the design is extremely compact with essentially no external components except for the clip and the bolt return spring (which will likely be covered by a half-cylinder of PVC so it isn't exposed to fingers getting caught or the mechanism being jammed).

EDIT: Added two sentences that clarified how the breech elements are nested.

This thread is for the information of all those attending the first MANIAC. Official details below. If you are coming, please leave a post saying you are coming, what guns you are bringing, and who (if anyone) you are bringing. Please no discussion as it will clutter things, if you want to discuss or ask questions please use the thread started by Team Slaya.

What: Massachussetts Area Nerf Interests And Competition, MANIAC

A get together of fellow nerfers from the Massachussetts area.

When: Sunday June 26, 2005 11am-5pm

We begin nerfing at 11 am, and will have everything packed up and cleaned up by 5pm. My advice to you: if you want to check out the competion, or just shoot the breeze, as well as recieve instruction as to where and what we are doing come 30 - 45 miiutes early. We will nerf without you if you are late.

Also, we will stop around 2 for a lunch break, if you want to eat, bring a packed lunch, as I have no idea if there is any eating establishments nearby.

Why: Because we like you... M-O-U-S-E

How: Banned is anything that shoots over 150 ft, for safety reasons. If you think a gun is questionable (SM5K, Titan, homemades, or others), bring it, and we will take a look at it. Chances are it will be a no to the usual banned weapons, but if your homemade shoots a reasonable range (ie 50-100ft) than chances are we will allow it. If anyone doesn't want you using it, it will be banned

Protective eyewear (ie sunglasses) mandatory

Please be sure to bring as many darts as humanly possible. I will be bringing around 200. Also, mark your darts with a letter with sharpie, not all FBR is created equal.

We will be playing most of the standard games, deathmatch, team deathmatch, CTF, pistol wars, etc. I am open to reasonable suggestions for games when we get there. Teams will be randomly chosen.

Where: Menotomy Rocks Park, Arlington, MA

Directions:
From outside Boston take I-95 to Exit 29A, Route 2 East. Proceed on Route 2 to exit 59A, Pleasant Street. Make a left onto Pleasant Street. At Massachusetts Ave. make a left heading west toward Lexington. Make a left at Jason Street. Proceed on Jason Street through a four-way stop at the Gray Street intersection. Menotomy Rocks Park will be on your right on Jason Street. You will see a wrought iron fence, a stone wall with a small sign, a bulletin board and an open field.

Address:
125 Jason St, Arlington, MA
Yahoo Maps
Mapquest

My contact information for questions/comments/concerns:

aim - userjjb8686
email - userjjb@yahoo.com

if your parents want someone to talk to or to ask questions, contact me and I'll give you my phone number.

When I first picked up the Tek 6 I thought it had good potential, even though the plunger tube is a little narrower than a NF tube, it seemed like it had good air output.

The main reason why it gets crap ranges is two-fold. First it's a rotating barrel, so there are seal problems. Second, there's a big bottleneck for the air right after the plunger tube, the hole is barely a centimeter in diameter. In this mod I eliminate both problems.

The first thing to do is take the gun apart. There are screws in the main body of the gun, as well as the slide. However, there's another one hidden under the slide, so be sure to take off the slide, and remove that screw, before you pry apart the gun and break it.

Here's the gun internals (post-mod, no before pictures sorry):


When you open it up, remove the turret, as well as the long stepped sliding piece thats right below the turret, you won't need these.

Next, take out the plunger tube. Your goal here is to get a piece of brass to fit on the end with a hole in the end of the tube as wide as the brass. Here are some pictures of what to cut and what not to cut off:

At the far end of the tube carve out a hole where the piece that connected to the turret used to be as wide as your brass:


Be sure to leave two sections of the end, the screw hole where it attaches to the case, and a crosspiece that slides into a slot in the case, this will keep the barrel secure.




Take your new barrel (I used a 4 inch piece of 17/32 brass), and goop a whole bunch of epoxy around the new plunger hole as well as on the two remaining chunks. Let this dry for a couple minutes.

Now you need to cut the case to fit the new barrel. Carve out a circular chunk on each side of the case, it's more trial and error than anything to get the right fit




Now you should have a larger hole that looks like this:


Now put the new barrel/plunger assembly back in the case. You may have trim some of the epoxy off so that the notch fits into the slot on the case. Put all the parts back on, and screw it up, and voila:


Range testing with 20 shots flat gave an average range of 62ft.

With a spring replacement it could rival the NF, but what I really like about it is the feel. It's smaller than a NF, and the circular end of the gun makes a very comfortable grip for two handed firing. Also, the plunger is excellent and has such a superb seal, to reload all I need to do is put the dart in the barrel a lttle, and when I cock it, it draws the dart right into the barrel, speeding up reloading.

I was wondering if someone could give some of the crossbow's dimensions. Specifically, I'm looking for:

The inner diameter of the plunger tube.
The length, diameter, and wire thickness of the spring.
How far the plunger head travels from a cocked to at rest position.

If you happen to have these figures on hand, or don't mind opening your crossbow up and measuring that would be great, but some fairly accurate guestimations are welcome as well.

Well not really anything of valuable contribution, so I figured Off-Topic is the way to go, but anyway its sort of a funny little incident.

For my first mod (nested brass barrel for NF) I was looking everywhere for some brass, I found a couple places, but they would have needed to order it, and I'm a very impatient person so I ended up calling a bunch of places seeing if they had it in stock. By happenstance one place recommended me to another, who recommended me to yet another. Anyways this place happened to have a few sections in stock and I plan to go today to pick up my reserved sections.

Simoultaneously and somewhat independently I've recently been scouring local thrift stores for old Nerf guns (can't wait until summer garage sales get in full swing), with no luck so far. However, in a somewhat parallel manner one owner of a thrift store tolled me of some stores called Children's Orchards which sell children's used clothes etc. as well as maybe selling used toys (bingo).

I was looking online for the best route to each when I realized something. They are both at the same address! As in 446 Boston Rd, Billerica. Holy crap! Talk about one stop shopping huh?