36 replies to this topic

[ricochet]

Introduction:
I have always been wanting to build a magstrike piston from the ground up, but also modify the design a little to allow for increased volume and capability of being integrated into a breech system to work with clips or magazines like in the stampede, longshot, etc. So, I got to work and came up with this:

It is about 11 inches from end to end including the brass breech, so it is much larger than the magstrike version. The increased size is for increased volume and to accommodate a 2 inch breech. The cylinder is 1 inch cpvc.

Internal Pictures:


These two photos show the front portion of the piston in the retracted and forward positions that occur during firing.

Front Seal:

This was the most frustrating component of the piston. I tried 6 different front seals, and this is the most reliable. It consists of a rubber washer glued to a piece of .5 inch pvc. The ID of the washer is 3/8 inch. The pictures below show the concept of the seal since the actual one is glued in the cylinder of the piston.



Sealed


Seal broken

Video of the piston when pressurized:
Video

I tested the piston with a 14 inch brass barrel and got ranges of 80-90 feet flat. I will be making a second piston with a small improvement soon, so keep your eyes pealed. Once the second one is up, I will hopefully work on a write up. Feedback is welcome and encouraged.

Edit: The piston used 1/2 inch nylon tube, 3/8 inch nylon tube, 1/4 inch nylon rod, two different springs, 17/32 inch and 9/16 inch brass, and a 7/8 inch U-Cup seal, all of which were purchased from McMaster. The rubber washer, pvc, cpvc, and metal washer can be purchased at your local hardware store.

Edited by ricochet, 03 January 2011 - 07:56 PM.

[roboman]

Very nice! I had been thinking about doing this for quite a while, but my plans never came to fruition.

[TxNerfer]

Great work. I anticipate the writeup, as well as a simple diagram of how it works? If you could get this to work with a hopper, it would make for a very fun gun to dick around with.

[ricochet]

Great work. I anticipate the writeup, as well as a simple diagram of how it works? If you could get this to work with a hopper, it would make for a very fun gun to dick around with.

I plan to post a diagram and explination when I post the writeup for those who are unfamiliar with the magstrike piston. If you can't wait, search for a magstrike piston dissection on the forum, I know there is one around here somewhere.

[knexpert66]

Nice, man! Way to get a Magstrike type system to get in the 80's.

Edited by knexpert66, 30 December 2010 - 11:32 PM.

[Wes7143]

That is a very lovely rate of fire. Based off the physics of the original magstrike, that leads me to believe that it's giving off a decent amount of air each time. I'm interested in seeing this thing with a barrel and hopper.

[Boot]

Nice!

This is exactly where I originally wanted to go with the Mirage (Link in sig) although I felt that fabricating a MS valve from scratch would be much to time consuming (in terms of finding the proper materials), so I went for a different approach at achieving high ROF and volume (using back pressure valves for a more controlled semi-automatic setup).

When I do get around to building the Mirage 2.0 it will be interesting to compare it to the completed version of this. I am very interested in seeing where this goes since the idea of hooking this up to a vertical magazine is exactly like the continuation of the original Mirage!

[shmmee]

Seriously awesome first post! I think it's safe to say that that we're all looking forward to seeing where you go with this next. What psi were you running at for that test? 80' full - auto? That will be a serious gun to contend with if you aren't spending your entire time pumping.

A write up explaining magstrike piston theory was done by "Gas Mask Guy" and can be found here:

Magstrike Firing Mechanism Autopsy

[Green Wing]

Very impressive. I can't wait to see the final product!

[thedom21]

I am very excited for the write-up!

[ricochet]

Seriously awesome first post! I think it's safe to say that that we're all looking forward to seeing where you go with this next. What psi were you running at for that test? 80' full - auto? That will be a serious gun to contend with if you aren't spending your entire time pumping.

A write up explaining magstrike piston theory was done by "Gas Mask Guy" and can be found here:

Magstrike Firing Mechanism Autopsy

I ran the test around 70 psi and put a 14 inch piece of 17/32 inch brass on the front and shot a single dart. Yes, I know that is rather large psi, but pumping shouldn't be much of an issue seeing how I plan to use an air compressor and a 2 liter tank in the gun I am going to make. I aim for around the size of a longshot, but have larger magazine capacity. Also I calculated that a single magstrike tank, when modified, holds about 1/3 liters of air. The gun obviously won't be out soon due to the fact of making a second piston and a writeup first.

Edited by ricochet, 31 December 2010 - 12:35 PM.

[Exo]

It looks very cleanly machined. Does the piston drop all of the air that's in the pressurized piston, or does it drop only some of it, like the MS?

I couldn't see the video, but it sounded fairly fast. MS's can drop all ten shots in about one second, which makes them hard to use for single fire, but great for bursts and sprays. It sounds slow enough to be useable for semi-auto, but fast enough for good-spaced bursts.

Nice job, I can't wait for the final version.

[ricochet]

It looks very cleanly machined. Does the piston drop all of the air that's in the pressurized piston, or does it drop only some of it, like the MS?

It should release all the air, it functions exactly like the MS piston. As the pressure reaches the pressure needed to fully compress the main spring, it breaks the front seal until releasing all the pressure that is inside the piston. Does that help at all?

[Exo]

Yeah. I was just wondering because in my experience, the MS piston stays partially pressurized right after firing, not shrinking all they way back down to normal size, which would explain why you have to pump more to get the same amount of shots if you don't blast the entire clip in one trigger pull.

[TantumBull]

Wow, that is fucking sick, man! Really nice design and execution. Like Wes said, I'd love to see this puppy with a hopper!

Oh, and this:

As the pressure reaches the pressure needed to fully compress the main spring, it breaks the front seal until releasing all the pressure that is inside the piston.

is an awesome way to summarize how an MS piston works in one sentence. Props.

[ricochet]

Like Wes said, I'd love to see this puppy with a hopper!

I am not very familiar with hoppers and was planning on simply using spring loaded magazines. Then again, I will have 2 of these soon...I'll look through some threads and maybe try it out.

[NerfGeek416]

Like Wes said, I'd love to see this puppy with a hopper!

I am not very familiar with hoppers and was planning on simply using spring loaded magazines. Then again, I will have 2 of these soon...I'll look through some threads and maybe try it out.

Hopperz

[roboman]

If you're going to use a hopper, there are other ways to achieve this type of "pulsed air," without the reciprocating piston. A pop-off safety valve attached to the pilot side of a QEV (Quick-Exhaust Valve) could be much more efficient, if used in conjunction with a hopper. I think a MS-style setup would work much better with a breech and a spring-loaded magazine.

[ricochet]

I think a MS-style setup would work much better with a breech and a spring-loaded magazine.

Exactly my thinking, but I will it in try both time permitting.

[roboman]

Here's the link to the pop-off + QEV, if you're interested. I'm sure a similar setup could be done with an adjustable pop-off and, say, your average backpressure tank. Hmm, this gives me ideas...

[KaneTheMediocre]

According to mcmaster:

"Pop-safety valves automatically "pop" open at a set pressure and remain fully open as long as the pressure is above this point. When the pressure level drops back to the set pressure, the valves instantly close. "

I'm not doubting that these work, but it would seem preferable to find a valve that takes some time to reset. Theoretically, these shouldn't work--The valve would close as soon as it opened, maintaining the rated pressure rather than allowing for the pressure to (relatively) slowly oscillate, building up and suddenly releasing. I bet such a slow-reset OPRV exists, but I have no idea what it would be called, or where to find it.

[Forsaken angel24]

I am also looking forward to seeing where this goes.
If you do a write up on this, I will follow it and maybe modify a few things along the way.

[ricochet]

I am also looking forward to seeing where this goes.
If you do a write up on this, I will follow it and maybe modify a few things along the way.

I was hoping to find a few members like you. I know I am not the only person who sees the potential in these, and by having other members modify the design, the reliability and performance may increase. I have never done anything with valves and pneumatics until this piston, so I am very limited due to inexperience. I really appreciate people willing to take something I built and modify it. Its an honor.

[roboman]

According to mcmaster:

"Pop-safety valves automatically "pop" open at a set pressure and remain fully open as long as the pressure is above this point. When the pressure level drops back to the set pressure, the valves instantly close. "

I'm not doubting that these work, but it would seem preferable to find a valve that takes some time to reset. Theoretically, these shouldn't work--The valve would close as soon as it opened, maintaining the rated pressure rather than allowing for the pressure to (relatively) slowly oscillate, building up and suddenly releasing. I bet such a slow-reset OPRV exists, but I have no idea what it would be called, or where to find it.

The thing is, the pop-offs pilot a back pressure valve, such as a QEV, which will remain open until the chamber is refilled. If the pop-off triggers, the tank will dump its contents, equalizing itself with the atmosphere, which, in turn, resets the pop-off. Compressed air then enters the tank, re-seating the piston, and continuing the cycle.

Preferably, the air will nter through a separate, smaller hole, to slow down the refilling process, and thus, the rate of fire. One could even use a flow-control valve on the air input to control the ROF.

[ricochet]

As requested, here is the write-up for my magstrike type piston.

Materials:
McMaster:
U-Cup Seal - 9691K52
.028" wire spring - 9637K68
.047 wire spring - 9637K82
1/4" nylon rod - 8538K14
3/8" nylon tube - 8628K51
1/2" nylon tube - 8628K28
Hardware Store:
7/8"x3/8"x1/16" metal washer
7/8"x3/8"x1/16" rubber washer
1/2" pvc
1" cpvc
2x 1" cpvc end caps
2x < 1/8" nail
1/4" barb
Electrical Tape
Super Glue
PVC Cement

*17/32" brass from your preferred supplier*

Tools needed:
Hacksaw
Pipe Cutter
Dremel
Sand Paper
Metric ruler



Sand down the barb so it fits in the 3/8" nylon tube and super glue into a 12.5 cm length of the 3/8" nylon tube.


Super glue .7 cm of the 1/2" nylon tube onto the 12.5 cm 3/8" tube like so.


Drill a hole through the previously combined parts and super glue a nail into it like shown in the picture above. Leave it long or trim it, it depends on how the piston will be installed to your gun of choice. It is necesary to provide strength for the previously combined components.


Drill a hole SLIGHTLY larger than 3/8" into one of the end caps in the CENTER. You must be accurate, or else the piston will not work.


Slide on the end cap onto the piece above like so.


On the opposite end of the barb, mark a 2.2 cm line.



Add 10 cm of the .047 wire diameter spring followed by a .5 cm piece of 1/2" nylon tube. Super glue the 1/2" piece at the 2.2 cm mark, shown in the picture above.


Add the metal washer and super glue it above the recently added .5 cm of 1/2" nylon tube.



Add the u-cup seal above the washer and super glue the edges to the washer while pulling down. This will make it slightly expand providing a better seal, I tried to demonstrate in the first photo above, though it is a tad blurry. It should look like the second photo once completed.



Add a piece of 1/2" nylon rod above the seal so it is flush with the end of the assembly, it should be .6 cm if I recall correctly.


Drill a small hole, mine is 5/64", at the end of the assembly. The picture above describes this best.

Edited by ricochet, 04 February 2011 - 09:47 PM.