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Hoppered Hamp

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#1 KaneTheMediocre

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Posted 08 August 2010 - 08:39 PM

Hoppered Hamp.

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So, very shortly after the HAMP was posted,
http://nerfhaven.com...showtopic=18962

I discovered that putting a hopper on them created a ridiculous assault weapon. Hoppers were easy to make, and a good HH could be made by applying the lessons of the tagger blasters.
http://nerfhaven.com...showtopic=18963
So, I didn't think that I needed a writeup for how to make a sweet hoppered HAMP.

Having seen a variety of hoppered-hamps created by the community, I decided that a writeup was necessary to protect the reputation of the HH, which many now see as synonymous with the HAMP. Also, I have refined the make of the HAMP itself a bit, and that's worth an update.

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The biggest timesaver and durability enhancement by far is the replacement of the cardboard/duct tape capping of the plunger head. If you chamfer the inside edge of the plunger, and the outside rim of the cap, you can hammer a 1" endcap into 1.5" PVC. Flat endcaps are much better for this, because you can set the cap on the ground, and hammer the tube onto the cap. RagrizInferno is responsible for showing me that trick, among others.

http://www.nerfrevol....php?f=9&t=1058

The flat endcap also allows you to easily integrate a check valve into the plunger head. This helps prevent sucking darts backwards from the wye, which can cause all kinds of bad things. This basically requires a hole and a flap. I did it with a piece of rubber sheet, and two small wood screws, as shown. This isn't the best or the only way to do a flap, but it works.

The alternative plumbing for an external check valve is generally uncomfortable or otherwise in the way. Note that not every HAMP should get a check valve--Singled blasters that muzzle vacuum load need to use that suction, as do blasters like the autoloading tagger blaster that otherwise use the suction from the draw.

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The next step is to make the air do a 180. Although it's possible to make a hamp entirely inline, it's an ergonomic disaster. Besides, the barrel comes in handy for a plunger guide later. First, cap the end. I don't care how you do it, but the easiest way is to just glue in an 2" endcap. Next, drill the neatest 5/8" hole that you can in the side of the endcap, as far towards the back as possible. Then cut a 3" + (size isnt important yet, you're going to cut it down later) piece of CPVC, and cut off one side of it as shown. This allows you to bottom out the CPVC in the plunger tube, and still get airflow. Next ream some PVC to 5/8", and sheath in around the CPVC. Then, stick it in to size it, and cut off the excess. Pop on an elbow, and use hot-glue / e-tape / bubble gum / epoxy / whatever to seal it. Note that it doesnt need to be particularly strong, as it will be structurally reinforced later, and perfect seal isn't crucial with HAMPs.

Edited by KaneTheMediocre, 13 August 2010 - 09:15 PM.

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#2 KaneTheMediocre

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Posted 08 August 2010 - 08:42 PM

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To make doubly sure that you don't suck any darts back behind the wye, put a nail through the wye. Ideally you should slant it, so it's sort of a dart ramp as well, but make sure it's a smooth nail if you do that.

Chamfer the inside of your barrel a la the hopper writeup. Loose, long barrels work best (ie sch80, or long PETG nested in sch40).
http://nerfhaven.com...showtopic=19569

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Make a spacer so that you can tape the barrel and hopper against the plunger tube without bending them. This will require a little extra something (i use cardboard) to make the spacer thicker between the barrel and the tube than it is between the hopper/elbow and the tube. Then tape it all down.

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Finally, you need to make something to hold the plunger straight, and to keep the plunger from being pulled too far in or out. This is CRUCIAL if you want your HAMP to last, and I don't see why so few people do this. I had a 1.5" to 2" elbow handy, (a 1.5" x 1.5" would work fine for this method) so I connected it to the end of the plunger, and drilled a 7/8 hole in it. Actually, I did that in reverse order, it works much better. Anyways, I had to do some dremel work to get it so that it held the plunger straight without rubbing, but once that was done it was super-smooth action. This is the first time I used that particular technique, usually I've taped/glued spacers between the plunger head and a guide tube around the barrel, but I like this much better as a handle. Anyways, if you cut your plunger tube to the right length, and firmly attach the elbow, the elbow will act as the "in" stop, preventing you from hitting the air entry tube. To make an "out stop, preventing you from pulling the plunger all the way out, just wrap tape around the barrel, just past the plunger guide while the plunger is pulled as far out as it can without exposing tape/yarn/whatever your plunger head uses.

Edited by KaneTheMediocre, 08 August 2010 - 08:49 PM.

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#3 TantumBull

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Posted 10 August 2010 - 12:43 PM

Loose, long barrels work best (ie sch80, or long PETG nested in sch40).

How loose exactly? Should it be an "airgun fit" or should it be loose enough to slide down the barrel material if the barrel was pointed downwards? I'm working on a variation of this currently and am just wondering if I need to pick up some Sch 80 or if I should use my 3 foot long PETG segment.
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#4 taerKitty

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Posted 10 August 2010 - 03:14 PM

Loose, long barrels work best (ie sch80, or long PETG nested in sch40).

How loose exactly? Should it be an "airgun fit" or should it be loose enough to slide down the barrel material if the barrel was pointed downwards? I'm working on a variation of this currently and am just wondering if I need to pick up some Sch 80 or if I should use my 3 foot long PETG segment.

From the horse's mouth (or at least hooves on the keyboard):

HAMP systems work well with long, loose fitting barrels. With tagger darts, which have been my primary ammo for these, I have had the best luck with ½” EMT steel electrical conduit, which was $1.35 / 10 feet at home depot. ½” PVC will also work, and in fact gets slightly better range, but it occasionally jams. In general, any material used as an “air gun” fit will work well--the EMT, despite a 5/8" OD, will fire streamlines from a HAMP, albeit poorly. So yeah, loose dart fit is good.


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#5 hockeyfights118

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Posted 10 August 2010 - 03:30 PM

Does the way you put cpvc inside the end cap of the plunger tube work better then having a bunch of reducing bushings? I use bushings on mine and I find it easier than what you did.
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#6 TantumBull

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Posted 10 August 2010 - 04:56 PM

Loose, long barrels work best (ie sch80, or long PETG nested in sch40).

How loose exactly? Should it be an "airgun fit" or should it be loose enough to slide down the barrel material if the barrel was pointed downwards? I'm working on a variation of this currently and am just wondering if I need to pick up some Sch 80 or if I should use my 3 foot long PETG segment.

From the horse's mouth (or at least hooves on the keyboard):

HAMP systems work well with long, loose fitting barrels. With tagger darts, which have been my primary ammo for these, I have had the best luck with ½" EMT steel electrical conduit, which was $1.35 / 10 feet at home depot. ½" PVC will also work, and in fact gets slightly better range, but it occasionally jams. In general, any material used as an "air gun" fit will work well--the EMT, despite a 5/8" OD, will fire streamlines from a HAMP, albeit poorly. So yeah, loose dart fit is good.

Yeah, I actually read that as well, but I was just wondering, as Sch 80 is quite a bit looser than PETG, and he suggested both. Simply because Sch 80 is a lot easier to use, I'll probably just go with that, regardless of any range loss/gain.
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#7 KaneTheMediocre

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Posted 10 August 2010 - 08:33 PM

As for sch80 vs PETG: I think flared PETG feeds better out of hopper clips than chamfered sch80. The PETG that I use is looser than sch80. That said, I always use sch80 nowadays because it's easier to get (mcmaster wins). Also, I can make a PETG/sch40 hopper faster than a sch80 hopper, so I don't see why people think it's harder.

As for the CPVC vs bushings: Although the cpvc method is much cheaper than bushings, my main reason is ergonomics. Sometimes I like to use the back of the blaster as a stock, and with bushing you have all sorts of craziness sticking out the back of the HAMP. It's really a matter of personal preference, as I can't see any performance difference between the two methods.


Also, in the quoted text, I meant to say "ID"

Edited by KaneTheMediocre, 10 August 2010 - 08:34 PM.

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#8 taerKitty

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Posted 10 August 2010 - 09:47 PM

@Tantum: apologies, didn't realize you read that already. (Have mercy the next time you see me downrange!!!)

@Kane: The ergonomics are important. Have you any HAMPs with some sort of formal butt stock plate? Using, say some pipe wrap, or a piece of rubber?

Oh, and very concise and clean writeup. Thanks!
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#9 TantumBull

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Posted 13 August 2010 - 01:12 PM

I recently finished a variation of this, and its consistently shotgunning 2-3 darts. Have you ever run into this issue? Its a modified water gun by the way (one of those push pull ones). The seal is the stock o-ring and is perfect. Its well lubed, but there's still some friction. I can move it pretty fast, but its much more tiring than a yarn plunger head I imagine. The barrel is 3ft of PETG nested in PVC. My darts have an airgun fit in PETG.

I might try nesting a bit of brass in the barrel today to make extra dart feeds less likely. What would you do?

Edit: I also have a check valve on the plunger head just like yours.

Edited by TantumBull, 13 August 2010 - 01:15 PM.

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#10 taerKitty

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Posted 13 August 2010 - 01:54 PM

It's a matter of where you can put a dart constrictor closest to the wye, and your dart length. For example, my wyes' pvc barrel has a piece of cpvc hammered into it, (then reamed smooth) so the dart falls out of the hopper, into the wye, and stops. I'm firing 1-1/2" darts. I've found that 1-3/4" sometimes fails to feed through choppers, and 1" will double-fire.

How are you constricting your darts, and what size are they?
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#11 TantumBull

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Posted 13 August 2010 - 03:54 PM

It's a matter of where you can put a dart constrictor closest to the wye, and your dart length. For example, my wyes' pvc barrel has a piece of cpvc hammered into it, (then reamed smooth) so the dart falls out of the hopper, into the wye, and stops. I'm firing 1-1/2" darts. I've found that 1-3/4" sometimes fails to feed through choppers, and 1" will double-fire.

How are you constricting your darts, and what size are they?

Are you talking about out of a regular hoppered gun or a hoppered hamp? My darts were 1.5" until I cut them all down to 1.25" so they'd worked in hoppered blasters that don't put out a ton of air.
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#12 KaneTheMediocre

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Posted 13 August 2010 - 09:10 PM

It's a matter of where you can put a dart constrictor closest to the wye, and your dart length. For example, my wyes' pvc barrel has a piece of cpvc hammered into it, (then reamed smooth) so the dart falls out of the hopper, into the wye, and stops. I'm firing 1-1/2" darts. I've found that 1-3/4" sometimes fails to feed through choppers, and 1" will double-fire.

How are you constricting your darts, and what size are they?


All I do, is chamfer the dart entry on the sch80, or flare the PETG if I'm using that. Our darts are 1 1/4" to 1 1/2".


It's a matter of where you can put a dart constrictor closest to the wye, and your dart length. For example, my wyes' pvc barrel has a piece of cpvc hammered into it, (then reamed smooth) so the dart falls out of the hopper, into the wye, and stops. I'm firing 1-1/2" darts. I've found that 1-3/4" sometimes fails to feed through choppers, and 1" will double-fire.

How are you constricting your darts, and what size are they?

Are you talking about out of a regular hoppered gun or a hoppered hamp? My darts were 1.5" until I cut them all down to 1.25" so they'd worked in hoppered blasters that don't put out a ton of air.


The number of darts fired is mostly dependent on the amount of time that sufficient pressure to feed the hopper is maintained. Your squirtgun HAMP probably has a longer stroke, AND you probably move the plunger more slowly due to the friction. One simple solution is to only use part of the stroke--as in, only pull the plunger out 4-6" (experiment, your case may vary). My first dedicated hopper-HAMP was much larger than it needed to be, and it frequently fired 2-3 darts if I used the full stroke, but if I only used the last 1/2 of the stroke, it reliably single fired. I still use this HAMP a lot, and it works great when used in this manner

Another factor to consider is that you have a MUCH better seal than the traditional yarn HAMP. The long-loose barrel advisory really only applies to the low pressure, low friction seal that yarn usually provides. A shorter, tighter barrel is better for the tight seal that you are getting, which (due to the shorter barrel) uses less air. So, basically, the smart thing with a springer fit is to make a much lower volume, shorter HAMP, or just give it a 1' CPVC barrel with the same long stroke to use it as a machine gun.

I guess the short story is that most of this advice really only applies to the traditional yarn HAMP. Nothing against squirtgun HAMPs, as there are many ways in which they are superior to the yarn ones, but they are a very different power system and need to be treated differently.

PS I added a handle to the body. I'll update the pics as soon as i finish the damn Aabow writeup, which is/has taken FOREVER.

Edited by KaneTheMediocre, 13 August 2010 - 09:14 PM.

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