The piston return may be Like the bore evacuator on a tanks main gun but not like that. Once the bullet leaves, the air has so much momentum and heat. It causes a deprivation of pressure sucking the piston back in. It would be interesting to see if you had a vented gas tube if it would still do it.

@elektro3000

Жыл бұрын

Agreed, I was thinking the same thing.

@davejob630

Жыл бұрын

@@elektro3000 So was I!

@pedrowangler

Жыл бұрын

Ha ha... 4th

@edwardmorley8359

Жыл бұрын

The piston should bounce back on rebound alone. The gas system behind it is likely creating backpressure that is causing it to bounce back out after the rebound. It should be similar to dropping a ball bearing on a hardened anvil. Hard to say though, but that does give me an idea. It's possible that putting a small port at the end of the piston travel will allow the air pressure to equalize in the piston chamber.

@LowTech820

Жыл бұрын

Ram Pumps Work on a simmilar principle, although this is a Way different Environment. Does high Pressure Gas work like a Liquid?

Thank you Mark, I felt the "I built that and can't remember how it's built" :)

As a Swiss lathe CNC machinist I love watching your videos because you explain the engineering aspect behind a lot of your systems and decisions. I have always enjoyed firearms and shooting sports and hope to someday combine that passion with my machining ability. Keep up the good work and content!

Best guess regarding the piston return: expanding hot gas cooling down, and losing pressure, and also escaping elsewhere. And then the now higher pressure normal room air, pushes it back? Then there's a slight pressure imbalance to cause the little bouncing (which is common in pneumatic systems.)

@tonypalmentera7752

Жыл бұрын

The loss of temp/pressure perhaps creating a vacuum as well...immense pressure can be created in a gas hose or tube by having differential temps on either end. In an extractor, for example, the solvent "chases the cold"...so keeping the destination colder than the starting place, things move along under high pressure. In this case, the cold is outside the gun, the gun is fired, which makes it relatively very hot, and as the bullet escapes the barrel, path of least resistance and all the pressure by way of temp difference might create a strong pressure within the tube. The bounce might be associated with the back and forth of pressures between the end of the barrel and open ejection port (especially after ejection of the heat sunk in the empty case), creating pressures in the opposed direction as well, causing the competing seesaw effect, with the higher pressure within the confined space of the barrel/gas tube combo winning over the ejection port. My guess.

@markfergerson2145

Жыл бұрын

I was thinking something similar. Pressure in the barrel can’t go back to atmospheric instantly. Pressure waves reverberate back and forth for quite a while. Changing the barrel length should change the reverberation and hence how (or if) the piston bounces. If so it should be possible to tune aperture diameter, piston mass etc. so that it doesn’t bounce… at a given atmospheric pressure. Probably making the piston mass large enough could stop it entirely.

@iJacker

Жыл бұрын

Why guess? Just model it and run a fluid simulation - shouldn’t need a supercomputer to see what the pockets of air are up to

Your gas tube isn't vented, so the piston stroke compresses the air behind it. Compression equals heat, hot air expands, so once the piston bottoms out, the super heated air expands and forces it back to the fully open position (likely helped by kinetic rebound forces.) But since the barrel is still under pressure, albeit less since the bullet by that time is either just about to leave the barrel, or has just left, the piston gets half cycled again, and then forced back forward by the compressed air behind the piston head There's a reason that most gas piston systems have vent holes behind the piston head

@gabewright2690

Жыл бұрын

I like your theory. I wonder if the gas is also being sucked back through the gas tube and into the barrel after the bullet leaves. Due to the pressure in the barrel being relatively lowered immediately after the bullet leaves.

@mathewfitzpatrick5645

Жыл бұрын

@@gabewright2690 I was thinking of that, could the piston be sucked forward with by the same effect that makes fume extractors in tank barrels work?

@Hati321

Жыл бұрын

@@mathewfitzpatrick5645 maybe the spent case acts a bit like a piston while being extracted, drawing a slight vacuum.

@nobeltnium

Жыл бұрын

if anything, the barrel is under vaccum, not pressure. Has the bolt open while the projectile still in the barrel (eventhough it's very near the muzzle end) there will be castratrophic failure. However i agree with the theory that the piston compressing air at the bottom end

@briana5715

Жыл бұрын

Yes, I agree. Pressure on the bolt side of the piston not decreasing as fast as the barrel pressure decreases plus venturi effect from the fast moving gas leaving the barrel. I wonder if you could get pressure related ignition of some lubricants in that space behind the piston head (leading to carbon build up and difficulty disassembling). I think the scar says not to lube it’s piston.

Stirling engine effect. The air behind the piston cools down enough for the pressure to drop drastically. The area around the outside of the bore of the piston is cold(er) as it moves out, so the metal causes the air to cool below what it was at, creating a sudden pressure drop, sucking it in like a vacuum force.

@hinz1

Жыл бұрын

And venturi effect, suction at gas tube from fast gasses moving inside the barrel, at atmospheric pressure, after bullet leaves the muzzle and breech is open.

@edwardscott3262

Жыл бұрын

The first steam engines made more power from the cooling steam creating a vacuum than they did from the steam. Hot gases cooling is a powerful thing.

Don’t worry Mark. I’m certain me and thousands of others will stay and watch anything you got and put out there cause it is super interesting. Many people might not get it but the ones that do are the viewers that you actually want. Doesn’t matter how many there are

Like AvE says, "Everything is a spring." It could be the elasticity of the piston itself is compressed during the push stroke that it springs back when the pressure stops compressing it. Basically, a harmonic rebound.

@vevenaneathna

Жыл бұрын

lol this would have to happen at the speed of sound in metal. "mach 1 in metal/iron" is approximately mach 20 in air. the amount of time that a metals density actually changes after a big force is applied is like a blink of an eye compared to the lifetime that it takes for a firearm action to cycle. the springyness of solid metal under pressure is actually the focus of how to make nukes more powerful with the same starting amount of fissile material. expansion due to heating is something different in my opinion. the difference is between the two is explained in quantum mechanics, where something can have more energy by spinning around or vibrating side to side instead of compressing in one linear dimension.... I believe the actual math for deriving the partition function (how much for each wiggly mechanism, free energy gets transferred to) is based on group theory which is a bit over my head.... but I imagine it is such that you would vaporize a block of steel before you could measure a change in the same block of steel due to its linear compressibility/elasticity.

@ф_стрелец

Жыл бұрын

agree

@craighansen7594

Жыл бұрын

Stated in a technical way, that's what I thought.

You know people like your business and your channel when you bring up a technical question and in a day you have over a hundred reasonable intelligent theories and people racking their brains. Although I don’t own one of yours yet, you still make my favorite 50 caliber rifle and I think you are one of the best guys in the gun world period.

Soccer and flying planes , that is awesome keep it up you and guys like Dragon Man are beasts proud to watch you guys can’t wait to meet you guys one day !!!

In my mind, there are 3 possible reasons, all probably contributing in conjunction with one another: 1 - The column of gas impinging upon the piston equalizes with atmospheric pressure after the bullet exits the muzzle. As this happens, a vacuum is created behind that column, pulling the piston forward. This phenomenon is similar in principle to what's used to optimize headers in internal combustion engines. Essentially, the gas tube in front of the piston (and perhaps also the barrel) act as a tiny car header. 2 - The elastic collision between the piston and the cylinder containing it causes it to bounce back forward, similar to bolt bounce. 3 - There is a small pocket of air around the piston's tail that is compressed as the piston moves backwards. This acts as an air spring that pushes the piston forward after the piston reaches its rearmost travel and the force from the propellant gas has sufficiently diminished. This is also probably why the piston rests in its foremost position even after bouncing against the front of the cylinder several times.

Once again, great job Mark! Always interesting and entertaining.

I’m so glad you make videos dude. For real thanks, they’re a treat.

Mr. Serbu ..... Thank you for everything you do for US ........... Everytime you do a PRESENTATION for. US there is something to Learn. Please keep the Message and Mission Coming ......... Thank you for your VIDEOS Sir.

I love it when you upload

I have nothing to say other you do amazing work Mark. Thank you for sharing your thoughts and findings here.

Always enjoy the content.

Always great to watch a master craftsman at work :)

Hi Mark I enjoy your videos they make me learn a good deal and enjoy it you present the info clearly and quite well

The back side of the piston is staying pressurized longer than the port side due to the gas checks? Man that’s cool! Never would have thought. Thanks

My guess is the same the gas is slipping by causing vacuuming around the piston I appreciate your video's they are extremely informative and interesting

Working on a semi auto .50 myself. Thanks for the knowledge.

We love what you do, thank you so much and because of you I have a questionable hobby in Ca. Im on my 3rd "build" now

I’ve learned so much from you in the last few years, I’m really appreciative of all you’ve shared with us.

Hey regardless of what the algorithm says you have the best channel on KZread for what you do keep doing the good work

Thank you for the videos I've enjoyed watching. As for the pistons return after having struck the bolt it would appear that the tolerance of the piston inside the cylinder is tight enough to not allow gas to escape around it, which is desirable and also brings up the vacuum in the rifle bore upon the round exiting - enough vacuum pull to retract the piston. Between the two factors I reason for the pistons retraction. I'm not going to get into all the math about it (lucky you) but suffice it to say that the same effect of return can be easily demonstrated by sticking a hammer to an anvil - the anvil has more mass/weight and easily repels the head of the hammer and the gas tube is pulling vacuum onto the piston from the vacuum created by the rounds existing the barrel (past the gas port on the block).

Blessed with another video from Mark and it's a 50BMG video Edit: maybe smaller diameter has helped create a vacuum at the speed it's moving not sure as I am a gun nut just not a scientific gun nut

Hi Mark, I would suspect that the piston movement is from a vacuum. If you think about it, the gases that are created by the initial explosion which propels the round down the length of the barrel are replaced by air after the case is extracted from the chamber, the air flowing down the barrel creates a pressure wave that extracts the air in the piston tube. You have a gas exiting the barrel which creates a vacuum as there is the seal created at the chamber by the case, once the case is removed, the seal is broken and this allows air to flow through the chamber and into the barrel which then flows past the gas port and sucks the remainder of the gas (or at least some of it) out creating a new vacuum which causes the piston to move or reset. I could be way off base, but this is just my hypothesis. I think you could test this by hooking up an air compressor and cycling the weapon, the problem is setting up the compressor so that it has sufficient pressure to cycle the weapon while having the barrel clear. I'm not sure how to make that happen. I can see this in my mind, I just don't know how to transition it to words.

@Eluderatnight

Жыл бұрын

No its the temperature doing the vacuum. Pv=nrt. Initial temp/pressure spike. Pressure drops to ambient. Temp drops lowering pressure bellow ambient.

@edwardscott3262

Жыл бұрын

I think one side of the piston the side with the shaft also acts as like a gas strut. I don't know if there's enough clearance there for the gases trapped to vent. So one side creates a vacuum like you say and the other has compressed gas trying to push the piston back anyway. A double team effort to push the piston back to it's original position.

thx it's always interesting ,i can't help with any ,but keep the video coming i realy enjoy it ,thx again!

I’m just learning your product so I’m subbed for now.

I am here for the long haul. Thanks for sharing some inside baseball

Keep up the great work it is nice to see some come up with a new gas system rather than make another AR -18

Guns are obviously super neat, but I also really appreciate seeing a guy designing and manufacturing a real-life product. I am always trying to do that myself and have yet to find a need I can satisfy with my metalworking capabilites.

That's really neat. I think the piston is being pulled forward by the vacuum caused by all the gas leaving the muzzle. That's how fume extractors work on tank barrels and the Lewis gun had a radiator that drew air from that same effect

This is normal as far as I can tell excellent video awesome content thank you for sharing this six stars brother

i think you nailed it with "vacuum"!

Could it be the vacuum, like you said from the bullet leaving the barrel? Interesting stuff Mark, too bad about your soccer game. 🤝🤝🇺🇸🇺🇸🇺🇸 Hi to Val and family!

Hang in there Mark, keeping an eye out for your channel and new episodes, only had to resubscribe once. you are not the only one, wish some one constitutional friendly would buy KZread.

Great video as usual. If people don't understand what your doing here, then it it their loss.

Good stuff! Vacuum was definitely my guess, some fun venturi effect happening

good stuff!

A very clever way to put a piston on a gun. The Armalite AR--18 had a free-floating tungsten rod in the bolt carrier to stop bolt bounce. Until yours is a squad machine gun a steel rod should do the job well enough.

The best part is the camo. That looks exactly like the foliage in P3X-797. Yours truly, Colonel Jack O'Neil SGI

I have two theories. 1. I would say that the unvented gas system and tight tolerances of the piston are causing the piston to pull just enough of a vacuum right as the bullet meets the gas hole. The piston travelling backwards pulls the vacuum from the gas line, and after the bullet passes the gas hole, the traveling air and equalizing air pressure sucks the piston back to its resting position. 2. The piston is acting like a bore evacuator on an MBT cannon. Just the sheer energy and heat of the round leaving the barrel causes air and gases to be pulled from not only the open chamber, but the gas system as well, which would pull the piston back to its resting position. Source: SDI is a wonderful school

I think its the bullet that when it passes the Gas port it creates a vacuum that, pulls the piston back in just like the pressure cycles the bolt and then the vacuum resets the piston its alsome can't wait to owe one of my own 50cals from you keep up the alsome work

Noreen Firearms has been doing something like this on their Bad News rifles . They mount the piston inside the receiver.

mate keep up the good work.

Main guess for return would be air-spring. Very simple. Looking at that CAD there's just no real place for air to go and it looks like a fairly right bore fit with the piston rod, so we can't rely on that properly balancing to atmosphere. If there was a better way for air to vent behind the piston it would just stay rearwards until the carrier comes slamming home. And then of course as piston hits forward, there's natural bounce of steel on steel plus the rearward inertia of the gun plus maybe some latent gas pressure though it seems the front side of the piston is well vented. I would think that the piston would have both the forward vent holes for the gas from the barrel to vent after the piston has made its travel plans known, and a vent behind the piston to get air out of the way. I've been dealing with stuff like this myself for a while now, so air spring damping used for its positive effects and mitigated for its negative effects has been a big challenge.

@markserbu

Жыл бұрын

@scottwatrous9740 Air spring is right! I hope to do a quick video to explain it. Thanks for the comment!

@mfree80286

Жыл бұрын

@@markserbu That's easy enough to take care of with a small flat on the bolt side of the piston. Can't spring air that's leaked out.

@scottwatrous

Жыл бұрын

@@mfree80286 Yeah, slots on the piston shaft would be a good option. Especially if it's a part that needs to be threaded into another: it's helpful to have flats so you don't need to whip out the vise grips 🤣🤣

I’ve been a KZread subscriber forever and subscribed to many channels that KZread may consider undesirable. Never once have, I been unsubscribed without me doing it. I’m also an IT professional, so it is quite perplexing when I hear about this happening. 🤷

Best guest for the bounce is it's a pneumatic spring between the piston and the ... front of the trunnion(? Sorry my terminology may be off). Or maybe there's some spring in the steel of those parts, but I could only see that happening on the first bounce at full extension.

You're getting an inverse pressure spike from the inertia of the gasses leaving the barrel and the sudden withdrawal of the bolt head from the trunnion. It's like a backwards water hammer, but with gas.

Thanks!

I love watching your videos. I always wanted to design guns.

I’ve had to resubscribe about four times and I’ve never unsubscribe

“Hey Mark, wanna do a video?” “Yeah definitely! Let’s start rolling!” “Are you prepared?” “Absolutely not.”

My theory is the gas in the tube is acting like a spring. It is under a lot of pressure when it pushes the bolt, but that pressure is suddenly released after the weight of the bolt is removed from the equation, causing a brief lower pressure in the tube that sucks the piston back, but then the piston compresses gas still in the tube which causes the piston to bounce back out a bit. Multiple, rapid changes in gas pressure within the tube basically.

Always can tell a pro by the spanner wrench and a vise-grip pliers 🙂.

Gas dynamics in the barrel lead to oscillation of pressure (waves moving down the barrel) and down the gas tube to a lesser extent. As the gas tube is a closed system, once the bullet leaves the barrel, the gas inside the tube now reverses flow. This gas now has inertia so it wants to stay in motion, causing a low pressure condition called rarefaction. The same effect is how tuned headers on an engine can pull exhaust out of a cylinder.

In the immortal words of Jerry Clower "Pie are round, cornbread are square. ". Maybe a little antisieze on that would be necessary ,to disassemble that stainless gas tube assembly.

Raghad Meziane, my brother, happy blessed Ramadan 👍👍👍🇲🇦🇺🇲🇨🇷

All I can say is I’m stoke just ordered my first 50bmg from you last week

Maybe add ports to the cylinder that bleed off the excess gas once the piston gets moving fast enough. That will also make less carbon get into the chamber and that may also keep the air pressure from bouncing.

As the bullet passes the gas port it can cause a temporary vacuum sucking the gas and piston in reverse order of operation. Also I think you should drill a port for the guide rod to keep it from moving and bouncing. It moving so much maybe causing some of the bolt bouncing and not locking.

does the bullet leaving the barrel create a suction on the gas piston and pull it back?

@skyhop

Жыл бұрын

No it wouldn't. There's a lot of pressure still in the barrel when the bullet exits. It's most likely air compressing behind the piston during its stroke, since there doesn't appear to be an exhaust port.

dude is like a mad scientist

Nice

Wow😳, hope for suppressor soon

As many others say it's probably the vacuum of air. Essentially pulling the piston back. But there is also a counter vacuum causing a bounce effect. It can also be a magnetic pull between the two. There is a video explaining it in detail but essentially when a metal object moves past another metal object there is a magnetic pull effect that takes place due to them passing each other. It may be a combination of the two

@Njazmo

Жыл бұрын

But lead and copper aren't magnetic, like iron.

...interesting!

Along with the air that's trapped on the rod side of the piston, that piston is moving extremely fast. The high speed video is deceptive to us because we except the behavior to be close to the speed the video is showing. The piston and the carrier are moving together very quickly until the piston bottoms out in the cylinder. Even though the piston is much lighter than the carrier, it still has a large amount of kinetic energy and momentum because it is moving quickly. At this point the carrier continues rearward with it's momentum and kinetic energy, while the piston experiences an elastic collision with the back/bottom of it's cylinder. Again the piston looks like it is returning forward at a casual pace but in reality it has bounced hard off the back and is flying forward quick enough to bounce again in the front of the cylinder. Now as to the half bounce and returning forward flush I'd say that has to do with all of the gas dynamics which would be more difficult to predict. A simplification of the gas dynamics could be to think about the difference in pressure across each restriction in the gas flow's path. The piston is not a perfect seal but is just a large restriction in the gas flow, so some of the gas will get behind the piston and into the upper receiver. While not exactly the same, the differences in pressure is very similar to the concept of voltage drop across resistors in a circuit. The first restriction is the gas port, a moderate restriction that allows a good amount of gas through but will still cause a noticeable difference in barrel pressure compared to gas tube pressure. Then you said the gas tube has another restriction in it but we can consider it to be a part of the gas port restriction. Traveling down the gas tube is a small restriction so little pressure is lost from the beginning to the end of the tube. The piston-cylinder gap is a large restriction in gas flow, but not a perfect seal, so the pressure behind the piston starts to increase above ambient. The piston rod gap is also a large restriction and the other side of this gap is ambient pressure, but because it is a large restriction this implies that there will be a difference in pressure between ambient and behind the piston. What makes this complicated is that the piston is now moving rearward and compressing the gas behind it that is already slightly above ambient, as well as the uncorking and evacuation of the barrel. But to simplify, we know that the gas tube and gas port are only a moderate restriction, but both the piston-cylinder gap and the piston rod gap are large restrictions, therefore any pressure contained in the gas tube should evacuate faster than any pressure trapped on the rod side of the piston.

Yeah, I think Temperature plays a role with that vacuum action on that bounce

My thought is that the piston striking the bolt carrier driving the carrier to the rear is actually bouncing off the front of the carrier. Two hard surfaces impacting. Throw a stone against a steel plate and it will bounce. What is surprising is that the bounce could overcome the residual gas pressure - UNLESS there were a gas cutoff limiting the amount of gas vented off of the barrel, AND that gas were vented to the atmosphere. In other words, if the gas pressure was no longer working against the piston, the piston would bounce forward as the carrier were driven to the rear.

Can the piston bounce against its housing? That’s pretty radical return to just be vacuum

I would think, as there are no vents ahead of the piston (behind it as far as positioning of the gun goes) that the air there has no where to go it compresses as the piston is forced back and then as pressure in the gas system drops it pushes the piston back in place. Hopefully that makes sense as I described it.

It returns due to vacuum, just like an exhaust in a 4 cycle engine. The barrel has gasses leaving the muzzle at velocity that eventually pull a vacuum due to the length/timing.

first comment before the one before mine. lol. I need one of those BFG 50 A !!

No a engineer. However, it looks like the piston has acted on the bolt and is already returning as the bolt opens. My guess is that the projectile has already left the barrel and as such it is substantial enough to create a siphon, or vacuum, effect significant enough to act on the piston. The surface area you spoke about in the video. The spent case is still creating a sufficient seal in the breach to not allow air to be drawn that way. Likely not what is happening at all, but my cent and a half worth of opinion. You’re welcome YT!

I live in UK still love thee vices mark !!😊

7:12 The piston rod return because the movement from the piston create a vacuum (drag) behind the metal piece. Add the hot pressure gas from the ammunition fired, that-dissipate quickly from the gas return conduite and create a low pressure zone too that pull the piston rod back in place.

I think you might be right about it being a vacuum caused by the intertia of the gas leaving the barrel. The initial bounce back could be rebound just like bolt bounce and the following few returns could be vacuum and bounce fighting against each other. Inertia of the piston while the rest of the gun recoils could be at play too.

As the barrel evacuates, the higher (now) pressure in the gas piston rushes out and has velocity. That velocity creates a vacuum, sucking the piston back forward. My guess, at least. I love the idea of the piston being where it is, but it would be nice to make it serviceable. Perhaps rigidly attached to the bolt carrier. This is essentially a hybrid of the Marshall Williams tappet and he Ljungman or MAS-49 style of direct impingement. Cool. How free-floated is the barrel in this case? It would make for a good semi-auto .308 class weapon. Maybe .338 Lapua.

@Njazmo

Жыл бұрын

If the barrel evacuates, you have a major malfunction.

Back pressure. The piston is dropping back and forcing the air down the tube and back through the gas port in the barrel, but it does so faster than the gas port vents the air. It could be the size of the gas port or it could be the connection between the port and the gas system. Either way, the hot gas pressure in the barrel is enough to throw the piston, but it has enough back pressure on its way back to bounce.

Immediately thought vacuum too from the pressure escaping from the gas port

My guess is pressure waves. The pressure is propagating in waves and what you’re seeing is the piston being drawn into the low pressure zone left in the wake of one of the pressure waves, followed by a smaller pressure wave to send it back up etc. to create a movement like bouncing. That’d just be my guess tho from when I used to study friedlander waves, stuff loves to flutter in blast waves because of that.

I think your onto something with the vacuum theory! Similar to a syringe when you pull on it in a sealed vial and it pull resistance! Or similar to a tank , there is enough pressure and heat that mainly the heat creates a vacuum!

My theory for the piston bounce: The initial closing action would be from recoiling after hitting the stop when the piston fully extends. Slight vacuum effect may be sucking justvhard enougb to keep it retarcted afterwards. Vacuum could be created ny a combination of cooking gas in the gas tube (it wouldnt have to dissapate much heat to create a small pressure difference) and the bullet exiting the mizzle might actually be sucking enough gas out the barrel to function as a piston itself... and a .50 bullet is a pretty large piston relative to your gas piston...

@MarkSerbu I can only guess that the reason that piston is going back into its "home" then bouncing is because the piston is either bouncing back off the carrier (which doesn't make a lot sense since the piston is still has momentum after sending the carrier rearward) or it could be that the piston is bouncing off its rearward stop, then going back "home" with enough momentum that it bounces a bit. A 3rd possibility is that the piston is being "sucked" back "home" once the gas pressure drops. Maybe there is some reason that a tad but vacuum is being created???

Possibly residual pressure behind the initial stroke that creates the momentary build up to push the piston again? Maybe, as other comments noted, a low pressure being restored to atmospheric pressure in the piston chamber. Something is pushing the piston in what looks like a rebound with nothing to rebound against, as you stated. I'm just bouncing stuff off the sounding board here, but now I need to know what caused this😆.

Hello Mark, Have you considered the idea that the projectile leaving the barrel may create a vacuum sucking the piston towards the gas impingement hole? It is a guess on my part but I do not have time to model it in the computer to confirm my suspicions. Perhaps there is another user out there who could do that for you. I also do not have enough information to do so anywayyou would need to know dimensions iand weights of the parts in question, as well as clearances and speed of the projectile. In addition the distance from the throat of the chamber to the hole drillled in the barrel (so youfcould calculate volume) etc As I said I do not have time so maybe someone else does? Love your videos. I would never unsub your sense of humor is very simular to mine Perhaps because we are of a simular vintage? LOL! Keep up the great videos Shame about the buttmaster but thems the breakes. (seriously since that was never available for sale in Canada as far as I know) How they even heard about it in the first place is beyond me.

Interesting

The piston bounce may be due to vacuum being drawn as the gas tube vents, the momentum of gas exiting a space can create a partial vacuum inside it, that may be what's causing the piston to return home without a spring, partial vacuum sucking it back as gas flies out of the tube, dragging the piston with it.

How do you calculate the necessary force to unlock and cycle the bolt and carrier? How do you translate this to pressure in the bore/barrel/chamber and the sizing of the gas ports/pistons? I'd also assume that you also have to take into account the length of carrier travel and how much spring is behind it too?

Very cool mr serbu. The diameter of the gas tube means alot of surface area to volume, that gas cools extremely rapidly.

definitely a vacuum effect. also what are your thoughts on brandon herreras AK50? is he crazy or just nuts?

First thoughts are along the same line as yours. The gas is super hot and pushing on the piston. The piston stops and so the gas gets the neat newton push back, maybe combined with rapid cooling it creates a vacuum

Hey Mark, just a thought, but in high performace engine/turbo set ups, we can see the same ish effect on Wastegates that dnt have enough spring pressur above the diaphram (like no spring basically). Im not gunna try to explain it, as im sure there is someone with a degree could do much better, but i understand it to be a combination of the forces at play, and the way combustion moves through a tube. It actually creates waves which im sure you know, andit may be getting some extra "bouncing energy" from the Wave Propagation. Im not sure by anymeans. What if be super interested to see, is are some of the Big Round AR-10 style pistons do the same? Another quick question, Have you had your hands in Brandons AK 50 build? I feel like you two would def nerd out on this stuff together. I love it myself!

Props on playing soccer at 70yo Mark!

I think the piston return is due to the gas not being able to escape past the piston, so once the round leaves the barrel and the cartridge is extracted the gas that was pushing on the piston pulls it back into its rest position as it escapes through the muzzle end or chamber end of the barrel.

I wonder what calculations around the gas cooling would look like. A thermal/absolute pressure probe in that area may well be interesting or something you could see in to. I saw a glass engine once, they're neat to watch. Is there a book that gives pressures/placements for gas ports and the likes on a semi auto rifle or is it more trial/error?

Re: the Piston Return. A total amateur guess with nothing behind it: Two things, one is the gas being sucked out by the pressure normalizing once the bullet leaves the barrel - pressure started what momentum finished, leaving a vacuum. Second is the heat=pressure dissipating quickly and leaving a partial vacuum and sucking the Piston back in. Either way I'm guessing it's vacuum. An alternate guess is there could be a small pocket of air in between the Piston and the Receiver end of the gas tube, so Fire > Gas > Piston > Piston compresses air > Gas pressure drops and momentum comes to a dead stop at the end of the piston travel > Compressed air expands, 'retracting' the piston by pushing it back to whence it came.