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"5. No, only use pipe that's marked SCH40 or SCH80. Gravity feed fittings should not be used with pressure either." -CaptainSlug
You should be careful here making a distinction. Schedule-40 and Schedule-80 are actually only designations of dimension, they actually don't say anything specific about working-pressure of a pipe. In order to verify a pipe is rated for pressure applications look for "NSF-pw". Pressure rated fitings and pipe will always have this designation. HOWEVER, they also typically come with other designations as well. Virtually all pressure rated pipe and fittings will have a NSF-dwv rating as well (you could if you wanted use NSF-pw PVC for drainage, waste etc, but it's overkill). So just because the pipe is marked with dwv doesn't mean it isn't also pressure rated, just be sure to check first.
Unless you can set the breech to stay open for a set interval of time, I personally would recommend avoiding a brass slide breech for this kind of system because it has a rather high tendency to chew up darts. This is why I've switched to using a ramrod system in my most recent design.
And just so you know, that "3-way solenoid valve" or directional control valve is going to have a very low flow rate.
I could easily use a small QEV (1/8" or 1/4") in place of the solenoid valve if flow was a major concern, I just would prefer to be able to actuate the pilot valve electronically rather than pneumaticly so I have thin wires running to the trigger rather than tubing.
However, please note that the solenoid is not what's providing the power for the launching of the dart, but rather the barrel-sealing piston. The pilot (filling) side of the piston is pressurized and pushes the piston forward against the portion of 1/2" pipe sticking into the 3/4" tee. The neoprene on the front of the piston seals off both the pilot and chamber allowing them to pressurize. Once the exhaust port of the solenoid is opened the pilot area behind the piston vents to atmosphere and the chamber pressure pushing on the outer area of the piston slams it backward. This unseals the barrel and allows the chamber to vent down it propelling the dart.
The flow rate of the solenoid can actually be quite low and still properly actuate the piston valve. Especially with the o-ring and check valve you can pilot the valve with low flow. I have a 2" valve (that can be seen in my Spudtech thread referenced previously) that I can actually pilot with a Schrader (tire/bicycle) valve and that has around a 6 ci pilot volume behind its piston.
I agree however that the most problematic out of everything is getting the darts to feed smoothly, we'll just have to see how it goes once I get everything together. A great many people already uses breeches like this albeit not automated, so I don't anticipate it being to troublesome.
I may eliminate the internal bolt action and just extend the length of the 19/32" brass to reach the piston. I'll have one less part that can break/has to be made. This would also have the side benefit of allowing this piece to be removed from the inner section of 9/16" brass for disassembly/repair.
One idea I've been throwing around is having the opening of the breech actuated by the trigger pull rather than a spring. This again removes additional moving and external parts and increases simplicity of the design. I imagine the trigger-pull as a two stage actuation. The trigger would have some free movement backwards before it came into contact with the breech slide, during this time it would actuate the valve. Once the valve is actuated the breech would no longer be held forward and now that the trigger engages the breech slide it would continue to move backward, opening the breech and chambering a dart. Upon trigger release the pilot of the valve would resume refilling and the breech would close again. This would make the design less jam prone I think, but unfortunately the design would no longer be capable of full-auto. I may try the trigger breech return if the spring breech return doesn't work out.
BTW, CaptainSlug what do you think of the Gas Gun Design Tool (GGDT), have you tried it out yet? I would think it'd be right up your alley. It's a really quick and accurate way of predicting muzzle velocities before you go ahead and make the darn thing. It's accurate to with a couple percent, IIRC the only thing it doesn't take into effect is the transfer of heat from the working gas to the gun, the guy who made it is the Lead Firing Officer at the US's China Lake facility.
EDIT: Threw in some ideas for potential improvements and mades some comments about GGDT.
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.
also the main problem is how to get barrel sealed from the air tank from the part of the piston, because they don't have something special for that.so that will take some time.
the operating pressure, don't know. i think something about 7-10 bar that is 100-145psi. but i don't know how many pressure my PVC can hold. so that will need to be tested first.
I know that some people have trouble finding proper PVC pipe or fittings in the UK, not sure about Holland though. My advice to you is to make sure that the piping and fittings you use are pressure rated. You want to use "solid core" PVC, it should have some sort of pressure rating on the side. I'd recommend trying to find a plumbing supply store, if anyone should have it, they would.
If for whatever reason you can't find pressure rated stuff, be VERY careful, try to pressurize it remotely to test it.
This next model takes into account the second (and more complex) force on the dart, air drag.
A little explanation of air drag will go a long way to hopefully illustrate how exactly it works. The formula for the force due to drag is F=1/2 p vē A Cd, where p is the density of the fluid medium, v is the velocity of the projectile, A is the reference area of the projectile (imagine a slice through the dart perpendicular to the direction of travel). and Cd is the coefficient of drag (it's a dimensionless number related the shape of the object). I'll save you the drudgery of calculation, for a 1 cm diameter dart, F=.1 vē roughly(in units of g*m/sē).
Here's where things get interesting.
One problem in calculating how drag force affects the dart velocity lies in the fact that it is dependent on the dart velocity. Drag slows the dart, which in turn changes the drag force in turn affecting dart velocity. This would normally be a job for integrals, however since the time of flight is relatively short, the drag force is "relatively" constant. (Go ahead and feel free to do out the integrals for the time dependent velocity function if you want, for our purposes the accuracy is unneeded and my approximation is sufficient.)
Now that we have the force, we can calculate the deceleration due to drag using Newton's formula of F=ma. a=F/m where F is the drag force and m is the mass of the dart.
Resubstituing the newly found drag deceleration into our formula along with a little creative rearrangement of terms we get:
d= v/t - .1vē/m
This formula actually came out better than I thought it would, the first term v/t is exactly what we had before in my first post. The second term modifies this, subtracting from the total range based on it's mass and velocity.
Looking at the second term, one can now clearly see the effect of the mass of the dart on range, the greater the mass of the dart, the farther it will go, up until a limit. It is important to note that this isn't a one to one ratio, if you double the weight of the dart it isn't going to go twice as far. Dart weight's effect is only noticeable if the dart is too light, or the dart velocity is high.
We can also answer the other question about a maximum dart range, short answer:no. Long answer: In order to achieve greater dart ranges, we need to increase the muzzle velocity of the dart. This isn't a problem at first, however we soon encounter a technical difficulty. The drag force is proportional to the square of the velocity, whereas it's directly proportional to the mass. This means as we increase the dart velocity we will have to increase dart mass exponentially. However, as long as you have a potent enough nerf gun, and resilient enough darts, there is no maximum range.
Before I end let me say a couple of things though. This post was intended to explore the motion of a dart through the air, exploring the effect of it's mass, as well as determining if there is a theoretical maximum range. There is still the consideration of the flight characteristics of a dart, as well as the method of propulsion to consider. Hopefully this has been helpful.
In order to predict the motion of an object, you need to consider all forces acting on the object, as well as the object's initial state. It is as simple as that. In our discussion here there will be two forces acting on the dart, gravity and friction.
To start off simple, let us imagine the dart in the ideal conditions of a vacuum. Here there is only one force, gravity, and the analysis of the motion of the dart is quite simple. The dart emerges from the barrel with some initial velocity v at a height h. For simplicity, let us assume it emerges from the barrel parallel to the ground.
Now lets resolve the forces. For our purposes we don't necessarily need to consider the force of gravity, but rather the acceleration due to the force of gravity, which at the earth's surface is 9.8 m/sē. Using an accepted formula d=gtē, solving for t we get t=√(h/g). At a height of one meter, this is roughly .3 seconds.
Now that we know the flight time, we can substitute this in a simple distance equation: d=v/t. The v is the velocity of our dart and t is our flight time. Thus, for a dart fired at 1 meter off the ground, the distance traveled will be v/.3 where v is the muzzle velocity in meters per second.
So for example, if you fire the dart at 6 m/s, it will travel 20 meters.
As you can see, in a vacuum a dart has no maximum velocity, nor does it's mass affect its range. However in real world conditions things are different, both of these answers will change once we factor in drag forces.
First: Scientifically, what is the MAXIMUM physical range that a stock micro dart can fly after being fired from a very high-power gun?
Second: How much does weight affect the range and flight of stock micro darts?
I only had a little bit of time to do this post. In a day or two I'll add a second part, adding on the effect of drag forces on the dart's motion.
In my opinion I doubt it could be built to be mobile. Let alone cost effective or safe. Then again, I could be wrong. Build it and prove us wrong.
Pretend the spring is a keychain and the firing pin is a key. Pull out one end of the spring so that the firing pin goes between the outermost coil and the next one, now just spin the spring, voila, easy and painless.
I can't seem to get the spring off of the firing pin. Is there some specific way to do this? I tried everything - pliers, cutting it, nothing worked.
Also, like I've already told some people, we will begin nerfing at 11, I recommend you get there at 10
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
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.
125 Jason St, Arlington, MA
My contact information for questions/comments/concerns:
aim - userjjb8686
email - email@example.com
if your parents want someone to talk to or to ask questions, contact me and I'll give you my phone number.
I'm sure his parents don't want a whole bunch of kids they don't know tramping through their house and making it stink up with epoxy and hot glue and dropping plastic shavings all over. I understand the fact that you're getting the brass there to mod your gun, but you can just borrow someone else's gun (my aresnal has grown, use one of them). Alternatively, I could just bring my epoxy and my pocketknife, which requires no electricity, and will work just as well as hot glue and a dremel.
Kiljhadh, how far is your house from the park? Is it walking distance? If so, modders could, theoretically, come to your house to mod, then walk over to the park with you. That would work better, for there is an obvious lack of electricity in the middle of a park.
Haha, you've never met a human before, have you? People are us unpredictable as... well, I can't think of anything funny, but suffice it to say they are unpredictable. However, it would seem we have at least a solid six, but could be upwards of ten.
Arcanis/userjb, could we have a set-in-stone headcount?
I created an official thread for the war, please post in there if you are going, leave the discussion in here to minimize clutter.
Shadic, I would loooooove some pictures of the park and the areas kiljaha mentioned, or motivate him to e-mail me, IM me, PM me, or anything. Finally, you are welcome to come to MANIAC if you want.
I don't know if this was directed at me, but I'm neither little, nor just rambling off physics terms. I'm actually two and half years older than you, and have just completed my second year as a physics major in college, so I know a thing or two.
And for you little kids who think you're so smart in physics because you can name off physics terms, listen up.
I wholeheartedly agree, the best way to figure out good designs is to experiment with them
The dart and barrel interaction can be learned quite in detail through some research on your own, and with the help of cx's "Darts and Barrels" article.
Actually it's 1.5"x1.5^2"pi, the plunger head doesn't travel the whole length of the plunger tube so it's only 1.5 inches in length. Also the area of a cylinder is pi*r^2*h, not pi*r*h
Now you look at the Nitefinder which is about 5"x1.5pi"
This remains to be tested, but I'm inclined to agree.
The tiny plunger loses some air through several ways when the Maverick is unmodded, but all in all if you cover some of those up then you only lose some feet compared to when it is singled.
Furthermore, the plunger seal is designed to be efficient and it's not going to make a difference for when you choose to single it or not.
It's called the spring constant normally, but its in units of acceleration times mass per unit length, in SI units thats N/m. I never said range is directly related to the spring constant, in fact I'm inclined to disagree. It isn't a linear relationship.
Do you even know what a spring coefficient is? It's directly related to the strength of it, so you just said "it depends on how strong the spring is." *gasp* I would have never guessed!
I agree, if all you do is make it airtight, as well as providing the dart with a better fit, and making better use of the air output.
userjjb, the only thing that affects the distance between a singled maverick and an unmodded one is the fact that air loss areas are removed and a longer barrel is placed.
This also remains to be measured, but I also think range won't be improved much. But! if all you do is assume then you can be placed with the likes of Aristotle and others who assumed things and had their intuition proved quite wrong, (you can thank him for making people think heavier things fall faster for 1500 years)empirical methods are the only true way.
The fact is, however, you can't make the barrel much longer because the plunger tube is so damn small and you only get half of it, and it's an extremely inefficient plunger tube design. So you might get 10 or so more feet, but you just lost 5 extra shots.
I mean no disrespect to you AirApache, I just feel it is appropriate to have some sort of rebuttal. Discussion is healthy.
Anyways, good luck footemps, and nerf on dudes.
Yeah, this thing is ripe for a sspb integration, that whole lower half is empty
Ya you should try an integration, it looks like theres plenty of room left in there for an at2k or sspb.
A word or warning, trying to do a multi-barrel replacement may be rather frustrating on two accounts. First, like I said in the mod, there is a miniscule diameter bridging between plunger tube and turret, as in: 1/8 of an inch. Anyone doing a turret mod instead of a single mod, you'll have to address that issue.
Secondly, the turret design on this thing looks like it was designed by a monkey. Even after you remove the air restrictors its not going to be close to airtight. It's gonna require some creative epoxy/hot glue usage to plug up the piss poor design. Here's a pic of the inside of the turret:
I chopped off the outer half of each barrel and then carved as much of the + shaped supports for the removed air restrictors as I could, but I still couldn't get a good seal. Also, you'll notice a slot on the nottom of each barrel. This connect all the barrels to each other. The only thing I could think of doing is either pouring mass quantities of hot glue on it and try to secure each barrel. Another possible solution would be to attempt to remove the bottom circular piece (you can see the lip beteween the main piece and the back piece), but that is heavily glued on. Either way, it'll probably be a pain in the ass, good luck!
No, unfortunately, it's not that simple. Take a look about what chiefthe said about the maximum kinetic energy density that they design the guns by and you'll see that yes there is "physics" to it. There are many non-linear effects in a spring gun, and it's not just the volume of air moved by the plunger. It's dependent upon the plunger seal, the amount of friction on the plunger, the spring constant, length of plunger travel, plunger tube diameter, barrel diameter, barrel length, and a bunch of other things. Congrats to you if you can construct a model that can take all those variables into account and give the dart range. If it were that easy then all you'd do is calculate out what all the optimum dimensons should be for a given range and have the perfect gun. Take a look at Cx's article on barrel choice and you'll see that there's more to nerf physics than what meets the eye.Alright what the fuck?
The physics...Yeah, that’s pretty much it aside from width. Well for what we’re doing anyway.
...regarding gun/dart range isn't as simple as, "Oh it's plunger tube is shorter, so it sucks".
It’s simple if two spring guns both have good seals, good spring, good barrels, good darts then the one with a plunger tube with a larger mass will fire further.
I wasn't saying you weren't innovative footemps, in fact quite to the contrary, I was trying to support your effort. Sorry if that was ambiguous. Good luck and be sure to keep us updated.
Is that innovative enough jjb?
Well if you look in the thread I just made on my Tek 6 mod, you'd see what I mean. RoF is useless (outdoors) if it shoots 20 ft. But if you single it, it might turn out to be a good single shot. The physics regarding gun/dart range isn't as simple as, "Oh it's plunger tube is shorter, so it sucks".
How could you be surprised with range? This thing singled would be equal to a scout. If you single it, then your ruining the point of a mav, its ROF.
I'm not saying a singled Maverick is going to be the best gun ever, but the important part is to innovate, experiment, create! If all you do is follow other people's mods and just replace barrels, nerf modification will stagnate. But if you're willing to take a chance and think outside the box, eventually you will be rewarded with unexpected results. It's a little thing I like to call "thinking".
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.
As for the time, if you guys want to come earlier or leave later that's fine, but the minimum range is 11-5. I thought 6 hours was a good length since it was suggested in the article on NH about organizing a war.
If you guys want to mod, come earlier than 11, we officially nerf at 11. Also, don't forget this is a park, meaning no good working surfaces (except maybe a picnic table), and no electricity for that glue gun. I'd suggest modding in the comfort of your own home.
Once Kiljadh gets the pics up and we agree on that place, we have to pick a meeting place in the park.
We have a fair amount of people. Good.
Everyone bring as much or as little gear(guns,stefans,etc) as you want, I'd recommend much.
Location isn't official yet, and the only place we have a fair amount of info on is the place Kljadh scouted out. 125 Jason St. Arlington, MA Menotomy Rocks Park. By his description it seems like the perfect place, I e-mailed him, so hopefully I can get in touch with him and see what the place looks like from his pictures.
Time: I'm gonna say 11-5. Not to early, and not so late that it cuts into dinner time. Tell me what you guys think of this.
As for the Titan, SM5K, homemades or other questionables, I think we shall adopt the policy that there must be a unanimous agreement for them to be used. If any person, even one, doesn't want you to use it, then we won't. Also, I think it'd be fair to ban outright anything that shoots over 175ish, for obvious safety reasons.
The age range is somewhere around 13-18 to the best of my knowledge. I myself am 18.
There is no "official" date as of yet, although it seems like it was good for most people, Kiljhadh how about June 26 (Sunday)?
MANO (temporary name)
June 25 - 3
July 2 - 0
July 9 - 0
(more people need to vote)
I'd say if we get 13 people or even 8-10 we'd be fine, especially since this is our first war. It looks (as of now) as if June 25 or July 2 will be the date. We need more people to vote, but I'd like to set some sort of concrete date soon, so speak up. The biggest thing missing is location. Yazz/Arcanis/Kiljhadh (or anyone else) I'd like you guys to scout out and submit three locations (if possible) apiece in you area and submit them. They shoud be someplace free of non-participants, with enough space and suitable cover, and should be either public areas, or private land that you have express permission to use (your own land, grandparents etc.)
Copper barrels on the other hand definitely add some heft to the gun. I used 1/2 inch L-type copper on my other AT2K and it definitely makes the gun front heavy.
As for range difference between the copper and brass, I haven't officially measured it, but the brass mod does go farther. Also I sort of worry that the copper barrels are going to rip themselves off because of their own weight. I'd recommend brass, but copper will do in a pinch.
However, I would say that RoF and accuracy are interchangeable. If you have a weapon that can pop off 8 darts per two seconds, with a 12.5% accuracy and a gun that gets of one dart per two seconds, with 100% accuracy, they may be vastly different in design, but still do the same job, hit someone every two seconds (statistically speaking).
Logistically speaking though, accuracy is better than RoF. If you have a gun with a high RoF, it also tends to have a long reload time, leaving you helpless for that period of time.
So in conclusion I would say a combination of range and accuracy is the best. Sure, if you can have all three that would be excellent, but I'm hard pressed to think of a long range, accurate, full-auto nerf gun.
Also it's pretty easy to mod. Here's a good write-up: link and here's a thread with many, many links to other write-ups: thread
Mod one of your AT2Ks, and use your Maverick as a sidearm. Maverick mod
Alternatively, the NiteFinder is an excellent sidearm, with almost double the range of the Mav, at the expense of ROF. You can find the NF at TRU, Target, Wal-Mart, etc. Here's a mod
The BBB is an excellent primary, however it's more suited to losing, which you said you don't do. Also I'd recommend holding off on modding a BBB until you have practiced some on some cheaper and more readily available guns, that way you'll be sure to do a good job on the BBB.
If you have any other questions, be sure to use the search function, it's an excellent way to find out info.
Welcome to NerfHaven
Also aren't most screen door springs stretch rather than compression springs?
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.