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The Snap-4bp

I got it all backwards!

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#1 Carbon

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Posted 19 April 2006 - 11:32 AM

Considering how the SNAP-3 turned out, I wasn't really expecting this to be the next configuration in the SNAP line. But, I was thinking about how small the pressure chamber has become...which made me remember a design and suggestion that davidbowie made way back in the first SNAP thread. He had suggested a bullpup configuration, and did a 3D mockup of what it might look like. It wasn't feasable at the time, due to the SNAP's lack of power and too long length. Well, both of those problems have been solved, so here's the SNAP-4bp (bullpup):
IMG_4398.JPG

I'm currently using one of my normal pump breech barrels.
IMG_4400.JPG

The charging pump:
IMG_4399.JPG

The pump is pretty simple: The plunger rod has a 1.2" washer on it, held in place with a cotter pin. I gutted out the supporting fins from the end of a 1.25"=>.5" PVC bushing, which turned out to be the perfect size to fit some 1" thinwall. This is glued in place, with two slots cut into it. The slide is 1.25" PVC, with two screws driven thorugh it, into the slots, but behind the washer. This allows the pump to push forward, charging the rod, but pull back for firing. Between that, and using a .5" compression nut for the plunger, makes this the lightest and shortest SNAP plunger yet.

All other parts are standard SNAP, just backwards (clothespin, plunger, et al.).

The bullpup config isn't just trendy; it actually solves a few problems. First off, the SNAP tends to get very long, very quickly, especially if I'm using a pump breech (28" or so). This makes the length more manageable. Second, the charging pump and the breech now move in the same direction, as opposed to opposite. It's screaming to have the breech connected to the pump, and a clip added (most likely an Angel Clip). The pump also needs a handle, as pushing away is a bit of a tough sell...a handle will make it easier. The barrel also needs to be reinforced/given guides to run through/lowered. The pump handle could also be internally sprung to return.

Haven't tested ranges yet, but the little bit of extra dead space doesn't seem to be an issue at all, based on less than 50' test shots (clear across my apartment with no drop).
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#2 davidbowie

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Posted 19 April 2006 - 03:39 PM

WOOO!

This is AWESOME!

I really hope you connect the two handles. That would just be too cool.

As a matter of fact, I was just thinking about this configuration the other day, and connecting the charging handle to a clip handle. The yellow jacket has a reliable enough clip for me to start thinking about clip-loaders again.
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#3 Carbon

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Posted 19 April 2006 - 03:54 PM

Thanks, db....and thanks for the original idea, as well! Yup, it's first on my "to do" list, to get the handles linked up. Well, probably second. First is getting the barrel bonded in place and supported so it doesn't keep swinging around on me.

I'll check out your yellowjacket clip. "Reliable" and "clip" haven't been words which have normally gone together in my designs.
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#4 davidbowie

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Posted 19 April 2006 - 04:03 PM

Well...fairly reliable. It's pretty simple, but I have nothing near a writeup. Actually, I think it's pretty similar to the clip on the SNAP-2.
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#5 ompa

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Posted 19 April 2006 - 09:33 PM

With the immense volume of your plunger(s), since you use such a larger size of PVC than I do, I'd expect that thing to at least get 80'. Why? Because the bolts I use, especially with something like the NEAR, have about 2 inches of dead space, which is similar to yours. The NEAR (just did some testing before I left for Baltimore. Speaking of which, What the fuck happened, I'm gone for 3 days and the site goes nuts.) gets around 80-90; I was suprised, and extrodinarily pleased with it. However, since your plunger has a larger diameter, and the guns seem to have similar lengths of dead space, yours should get far more range. I'd guesstimate around 90's+, so good luck with that.

For connecting the handles, I suggest cpvc; it's strong, and you can easily just run screws into both handle and barrel. I can take some pictures of the NEAR at my connection points if you'd like me to.

~ompa

EDIT: By the way, what size of brass are you using for your barrel? If it's what I think it is, I could tell you the solution to your reliable clip issue right away.
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#6 Carbon

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Posted 19 April 2006 - 09:49 PM

First of all, let me say that I am dumb, dumb, dumb.

I managed to break the prime rule of homemades tonight; before you test it, glue it down, or screw it down. With the odd form factor, I managed to forget to reinforce the stress areas with a few screws, like I normally do. So, when I took it out for range testing tonight, it blew up on me. It was a lot better than it could have been...it just broke into three pieces, and dented the barrel. The barrel is now fixed, and the parts screwed together, so maybe tomorrwo will be better.

I lowered the barrel, added a guide for the barrel, finally superglued the handle (works beautifully) and added a handle for the pump. It's still a bit tough to charge...still got a bit too much friction. Here's what it looks like now.

Posted Image

Actually, ompa, we'll probably end up getting similar ranges. I'm betting my plunger is still heavier than yours. I have a larger volume, but my acceleration is slower. You have smaller volume, but faster accelleration (explanation courtesy of Bolt). MY best shot after denting my barrel was 80'. A standard SNAP can clear up to 100', but averages about 85-90...we'll see how this goes.

EDIT: Just tested ranges; when I could actually find my darts, it was getting around 75'. Yes, it's a loss of range, but considering what I want to turn the 4 into - a pump action rapid-fire gun - that's really enough. I also think that my minimal plunger design gets less range than my PVC plunger design (about 5 feet less, it seems.). But, since I wanted a small plunger for this design, it's a necessary trade-off.

Edited by Carbon, 19 April 2006 - 10:15 PM.

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#7 davidbowie

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Posted 19 April 2006 - 10:40 PM

It looks like you've got quite a bit of unused plunger tube on there. Can you move the trigger forward at all, or is that as far forward as the plunger can go?
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#8 Carbon

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Posted 20 April 2006 - 11:18 AM

The full possible plunger travel is five inches. I'm currently using about four, four and a half. As it is, it's almost too much; trying to cock the gun backwards when the draw is that long gets a little difficult in the last inch or so. I gave the handle some serious reinforcement last night (super glue and zip ties), so I'm going to see if I can make it easier by doing it BBB style, giving it a pull and a push. It's pretty easy to cock holding the gun sideways in front of me, but that's not really the point. As it is, I've had thoughts about shortening the spring, just to make it easier to use...

Of course, I may have a better solution to the problem. My slots aren't perfectly opposite, so the pulling action is partially digging the washer into the bottom of the guide tube...which would account for some of my friction. I may end up adding a third screw and slot to my guide tube.

Edited by Carbon, 20 April 2006 - 11:19 AM.

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#9 sniper25

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Posted 20 April 2006 - 07:39 PM

That looks awesome :D. I think I would change the barrel, the barrel is to small

Edited by sniper25, 20 April 2006 - 09:04 PM.

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#10 ompa

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Posted 20 April 2006 - 07:56 PM

Fix your spelling and capitalization, please.

Try some gun oil or something in there, it might help a little (or alot).

~ompa
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#11 Carbon

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Posted 20 April 2006 - 08:02 PM

That barrel is longer than you think, sniper25; it's 12" long, going back into the PVC.

I'll give gun lube a try, ompa. I've been using silicone spray, but it doesn't seem to stick around very long...I seem to be relubing a lot.
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#12 ompa

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Posted 20 April 2006 - 08:22 PM

I use paintball gun oil in mine, mainly because the stuff is supposed to go on o-rings. I'm not an expert with oil or lubricants though, so I'm sure there is a more effective type of lube out there.

~ompa
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#13 sniper25

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Posted 20 April 2006 - 09:05 PM

ooohhh
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#14 sniper25

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Posted 21 April 2006 - 03:52 PM

I've just finished my snap 4, I got a little anxious. It works awesome, avg. 77 ft.
one thing im working on is a way to open the breech and charge the gun at the same time.

Edited by sniper25, 21 April 2006 - 03:55 PM.

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#15 Carbon

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Posted 21 April 2006 - 05:52 PM

Have any pictures, sniper25? I'd be really interested in seeing it.

I missed your edit the other day, ompa...I'm using 17/32 for the barrel, with 19/32 as the "pre-barrel". That section is 1" long, so I can get another inch pressed into the actual barrel, and not have anything jam.

Edited by Carbon, 21 April 2006 - 05:53 PM.

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#16 davidbowie

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Posted 21 April 2006 - 05:54 PM

one thing im working on is a way to open the breech and charge the gun at the same time.


...what makes this gun cool is that you can just attach them with a bar and, PRESTO! If you can build the gun, you can connect them.
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#17 Ronster

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Posted 21 April 2006 - 06:00 PM

...what makes this gun cool is that you can just attach them with a bar and, PRESTO! If you can build the gun, you can connect them.


But, wouldn't that leave the breech open consulting in an extensive amount of air loss?
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#18 davidbowie

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Posted 21 April 2006 - 07:08 PM

nope, at least, if I'm reading it right. I'm pretty sure that the pump handle is not directly connected to the plunger rod, but the screws going through it are pushing on a washer which is connected to the rod, so the handle returns to its original position once cocked.
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#19 ompa

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Posted 21 April 2006 - 10:18 PM

Holy shit you have some really skinny darts then, for that small of a barrel size. If the 17/32 is really tight, I'd suggest using 9/16 as the majority of your barrel, so you'd have a 3-step nested barrel.

~ompa
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#20 Carbon

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Posted 21 April 2006 - 11:22 PM

By the way, DB, you're reading it right....the handle returns home after cocking. I've been playing around with a system for connecting the breech and the plunger tonight. The main challenge is that the travel of the breech is about two inches less than the plunger. I have a system in mind to compensate, but I need another .5" CPVC tee....mainly because I hacked up my only .5" CPVC tee before I got the idea.

I did some experimenting tonight. First, I tried a new oil...although it's not exactly easy to get. I found out today that Xerox fuser oil is silicone based...and from my experience with it, it's light bodied, and takes forever to get off. I dipped the plunger head in it, and I've been lubed all night - it's still nicely oily, not gummy. I'll have to check and see if it gums up, but it shouldn't.

My other experiment was just for the hell of it; I tried the SNAP-4 with two feet of 17/32" brass, joined by a small length of 9/16". I've been noticing my darts fishtailing lately, with leads me to believe that I need a longer barrel than 12". I still got 60' with 24", so I think I might be able to gain some range with maybe 6" more.

17/32" is the size that seems to fit best...9/16" has my darts just falling out. 17/32" won't vacuum feed, but only just barely. I'll try nested barrels some other time, though...probably when I get more 9/16".

Edited by Carbon, 21 April 2006 - 11:23 PM.

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#21 sniper25

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Posted 22 April 2006 - 08:17 AM

no, but I'll take some, and post them.

If you did connect the breech and the plunger you could add a magazine.
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#22 sniper25

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Posted 22 April 2006 - 11:34 AM

this is my snap 4
C:\Documents and Settings\Compaq_Owner\My Documents\My Pictures\Picture 001.jpg
I used the breech in the homemade section
C:\Documents and Settings\Compaq_Owner\My Documents\My Pictures\Picture 002.jpg

max range is 95 ft
accurate range is 60 ft
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#23 Carbon

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Posted 22 April 2006 - 12:12 PM

You need to upload those pics to someplace before we can see them; those are just pathnames to files on your computer.
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#24 sniper25

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Posted 22 April 2006 - 01:35 PM

sorry I've never posted pics before

how do I?
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#25 Carbon

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Posted 22 April 2006 - 01:49 PM

Read this post..

Edited by Carbon, 22 April 2006 - 01:49 PM.

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