Autocockers: Efficiency vs Low Pressure?

[masterchiefmurph]

I’ve seen conflicting things and need to get set straight on the physics of mechanical dwell and the effects operating pressure has on Autocockers.

Lowering pressure is very popular these days but does it mean better efficiency? Or worse? Wouldn’t the valve be open for longer if pressure was reduced? I’m I sacrificing efficiency for a lower operating pressure or not? the internet confused me and I’m wondering wether dropping pressure with new Lazarus valves or tornados for 9/16 are worth it. Especially for eblades.


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[DocsMachine]

[cracks knuckles]

First and foremost, the operating pressure is irrelevant. The classic examples I've been using for years are the Phantom and the old Shocker. The Phantom generally runs on unregulated CO2- typically about 800-850 psi. And it's considered one of the most efficient markers available.

On the other hand, the old 'shoebox' Shockers ran at about 160 psi, and were horribly inefficient- what, 300, 400 shots per the 3K/68 tanks of the day? That's about what, two, maybe three pods and a hopper on a modern 4500 tank?

You tune the marker for efficiency. The op pressure winds up... whatever the pressure ends up being.

I've built some pretty nice 'Cockers that ran at 700 psi, and some that sweet-spotted at 155 psi. I've dealt with a lot fewer modern spoolers, but I'm given to understand there's some that will beat those numbers at 120-130 psi.

The big trick to a 'Cocker is that the parts have to work together. While you can just throw something together out of the used-parts bins and it'll work, if you want to start seriously tuning for efficiency, you have to match. The bolt has to match the valve, the hammer has to match the valve, the springs have to match the hammer, etc. and the timing has to work with that combo.

You can make any 'Cocker "low pressure" simply by dropping in an overweight hammer and heavy springs, but your efficiency, of course, falls through the floor.

The trick to 'Cocker efficiency is to minimize the valve open time. It needs to open fast and close fast- and while open, it has to flow just enough air, and no more. You then want that burst of air to expand as little as possible before it meets the ball. Those "big bore" bolts? They don't "add flow", they just give room for the gas charge to expand- which wastes some of its energy- before it hits the ball.

And going along with that, you need a good bore match. Too tight and energy is lost to friction. Too loose, and energy is lost to blow-by.

Doc.

[Pyrate Jim]

There is a certain rule of physics known as "Boyles Law" which states the pressure over volume is equal to volume over pressure.
In other words, one cubic inch of air at 500 psi is equal to five cubic inches of air at 100 psi.
Efficiency is achieved by finding the proper balance between the two for any particular marker.

[Trbo323]

[cracks knuckles]



On the other hand, the old 'shoebox' Shockers ran at about 160 psi, and were horribly inefficient- what, 300, 400 shots per the 3K/68 tanks of the day? That's about what, two, maybe three pods and a hopper on a modern 4500 tank?

.

My memory could be off but I'm pretty sure the manual boasted an "efficient" 500 shots from a 68/4500

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[minimag03]

If i remember correctly, AKA said they tuned their guns for efficiency and low pressure was just a byproduct.

The best thing you can do for efficiency is getting a spring kit and sweetspotting your regulator. As long as you have relatively new/decent internals, that should get ya 80% of the performance you'd expect from a cocker that's been tricked out with all the best parts.

[coyote]

So,

"Tuning" a cocker is dependent on a subjective goal.

Doc tunes for efficiency. He also plays what I would describe as mostly "outlaw" style games in Alaska with limited surrounding infrastructure.

My markers are tuned to my personal "feel". I am within 90 minutes of a dozen commercial fields. All of them offer all day 4500 hpa fills. Absolute efficiency is not a driving factor in my day of paintball. My goal might be to lower my cocking pressure rather than max my efficiency.That changes when I go to an event like Supergame where my approach to my gear might shift.

Tuning is a personal hierarchy of subjective compromise. It is not and objective orthodoxy.

[DocsMachine]

There is a certain rule of physics known as "Boyles Law" which states the pressure over volume is equal to volume over pressure.

-Boyles really isn't particularly relevant here. The volume doesn't matter as much as the energy stored IN that volume.

The aforementioned comparison between the Phantom and the old Shocker: The Phantom uses a gas compressed to some 800 psi, and has a fairly efficient valvetrain. That is, there's not a lot of "wasted space" between the volume of full-pressure gas, and the face of the ball. Nearly all the energy of the expansion of that burst of gas, is used to propel the ball.

The Shocker, on the other hand, lets a charge of gas expand so that the pressure is down to about 160 psi. That energy is lost- you're "releasing the spring", to a certain extent. There's a lot less energy in that volume of gas, so in order to accellerate the ball to the same speed, you have to use more of it.

That is, of course, a heavy generalization, since there are markers today that work at the same or even lower pressures than the old Shocker, yet get considerably better efficiency. But the bottom line is that X volume of gas compressed to Y pressure has Z energy. The question is how efficiently that particular marker can use that energy.

In most semiautos- 'Cockers, blowbacks, spoolers, etc.- some of that energy is spent simply operating the gun. In a 'Cocker, some of the air is of course tapped off to run the pneumatics. In a spooler, some of it is lost to friction as it pushes the bolt back and forth. In a blowback, some of it is spent, well, blowing the hammer back.

In the case of a 'Cocker, there's not much you can do about the pneumatics- a smaller swept volume to the ram could conceivably save a bit, but the trade off there is you have to use a higher pressure. Boyle very much applies there.

In that case, you want to have the pneumatics 'spend' as little energy as possible- lighter bolts and back blocks, lighter springs, a lighter hammer.

As for the rest, as I said, the trick is to only open the valve just as long as it needs to make velocity, and no more. The Tornado valve was, in my opinion, one of the best- it had an extremely lightweight cup seal, and so cycled quite fast.

The problem was, that people would fit heavy hammers and heavy springs, so that no matter how light the cup seal, it took comparatively forever to overcome the inertia of the hammer and pressure of the spring, to close back up. And when that person didn't get the efficiency numbers that AKA was bragging about, they declared it "junk".

Again, whatever the combination, it needs to be intelligently adjusted and tuned.

If i remember correctly, AKA said they tuned their guns for efficiency and low pressure was just a byproduct.

-Exactly. You're tuning for efficiency first and foremost. The op pressure is secondary- and largely irrelevant. If this particular combo is happiest at 350 psi, don't try to force it to run at 160, just because that's what your buddy's combo does, or because what some twit on Facebook thinks it should.

"Tuning" a cocker is dependent on a subjective goal.

-This, too. The only reason I tend to tune for efficiency- besides the simple professional satisfaction of the work- is that for years I never had an easy supply of HPA. I had to make do with SCUBA tanks that were always half-full, or expensive nitrogen tanks that started out at only about 2500 psi.

For somebody that has easy access to local all-day-air, it's a lot less important. Heck, shoot a VM-68 if you want.

Any reasonably decent combination of parts can and will get you a pretty nice 'Cocker. You'd almost have to work at making a combo that would get less than half a case per fill- and if you don't shoot that much per game, and don't have to walk half a mile to the fill stations, who cares?

(I once played a speedball game with a tank that was actively leaking- you could hear it from ten feet away. I was down to 1500 psi before the game even started- and I still got at least one elimination. 'Course, it was indoor, 3-on-3, and was all over in about two minutes, but hey. )

Doc.

[minimag03]

-Boyles really isn't particularly relevant here. The volume doesn't matter as much as the energy stored IN that volume.

The aforementioned comparison between the Phantom and the old Shocker: The Phantom uses a gas compressed to some 800 psi, and has a fairly efficient valvetrain. That is, there's not a lot of "wasted space" between the volume of full-pressure gas, and the face of the ball. Nearly all the energy of the expansion of that burst of gas, is used to propel the ball.

The Shocker, on the other hand, lets a charge of gas expand so that the pressure is down to about 160 psi. That energy is lost- you're "releasing the spring", to a certain extent. There's a lot less energy in that volume of gas, so in order to accellerate the ball to the same speed, you have to use more of it.

That is, of course, a heavy generalization, since there are markers today that work at the same or even lower pressures than the old Shocker, yet get considerably better efficiency. But the bottom line is that X volume of gas compressed to Y pressure has Z energy. The question is how efficiently that particular marker can use that energy.

In most semiautos- 'Cockers, blowbacks, spoolers, etc.- some of that energy is spent simply operating the gun. In a 'Cocker, some of the air is of course tapped off to run the pneumatics. In a spooler, some of it is lost to friction as it pushes the bolt back and forth. In a blowback, some of it is spent, well, blowing the hammer back.

In the case of a 'Cocker, there's not much you can do about the pneumatics- a smaller swept volume to the ram could conceivably save a bit, but the trade off there is you have to use a higher pressure. Boyle very much applies there.

In that case, you want to have the pneumatics 'spend' as little energy as possible- lighter bolts and back blocks, lighter springs, a lighter hammer.

As for the rest, as I said, the trick is to only open the valve just as long as it needs to make velocity, and no more. The Tornado valve was, in my opinion, one of the best- it had an extremely lightweight cup seal, and so cycled quite fast.

The problem was, that people would fit heavy hammers and heavy springs, so that no matter how light the cup seal, it took comparatively forever to overcome the inertia of the hammer and pressure of the spring, to close back up. And when that person didn't get the efficiency numbers that AKA was bragging about, they declared it "junk".

Again, whatever the combination, it needs to be intelligently adjusted and tuned.

Doc.

Funny you mention that about the AKA valves, their cupseal design, and issues with tuning. It reminded me of something.

The cupseal design point is interesting. I never liked the RAT 3 or ANS valves for this reason. Besides them being aluminum, they also used a very soft cup seal. I always felt like this made the valve harder to initially open because the cup seal 'held onto' the valve stem for lack of the better term. This is in comparison to AKA's cup seal, which is made of a hard material. Would love to hear your opinion on the subject Doc!

So you feel AKA valves work best with light springs and light hammer? That's interesting. AKA's springs are very heavy, similar or heavier than the red springs found in most kits. I rarely used them though, felt like the best results came from a valve spring slightly heavier than the hammer.

[Magmoormaster]

Not sure what you're talking about. Shocktech and ANS valves use a hard plastic cup seal.

[minimag03]

Did they change the design? They used to mount the clear plastic seal to the valve body itself, not the steam. Those seals were much softer/more mailable than most cup seal materials.

[Magmoormaster]

Every one I’ve seen were hard plastic. And Ravi’s old reviews imply they all were too. I’ve never heard of them being soft.

[glaman5266]

Nothing substantial to add, but I'll echo what others have said about operating pressure. It doesn't matter as much as one would think. It's in how all the parts work together in concert.

When I started playing regularly I used an A-5 and a JT Excellerator 6.0. (JT Spyder clone) The A-5 would get maybe 700-800 shots off a 20oz co2 bottle. But my JT, which I swapped the stock regulator for a gas-thru & swapped in a lighter hammer spring, would get 1000+ off that same bottle in near-identical conditions. I basically increased the operating pressure & swapped the hammer spring and got more efficiency.

The parts that work best together give the best results, regardless of operating pressure. Many Nelson-based paintguns get 30+ shots off a 12g because of how the Nelson platform was designed. Low volume, high pressure.

[minimag03]

that's pretty wild that a regulator was causing such an issue, most people would assume the opposite!

[glaman5266]

minimag03 It wasn’t really an issue in terms of efficiency. I just didn’t want to deal with a subpar regulator. So I simplified it.
Running straight bottle pressure had me shooting hot. The weaker hammer spring got it down. It just happened to be a magical combination, lol.
Just goes to show that running high pressure isn’t a bad thing in terms of efficiency or consistency. The only reason I would want to run lower pressures is for a softer/smoother shot. But even then you can get something acceptable with the right parts or DIY mods.

Overall, I just hate dicking around with regulators, lol.

[Magmoormaster]

So,
Tuning is a personal hierarchy of subjective compromise. It is not and objective orthodoxy.

QFT

Personally, I like tuning for lower pressure. I like it for 2 reasons: first and foremost, it's more quiet. Not so much for sneaking, I just hate loud guns haha. Second, low pressure means less explosive force hitting the ball. And secretly reason number 3, I do it for the bragging rights. Doc is right that is not always most efficient to go low pressure, but it is also true that most of the very efficient guns run at under 200 PSI. There are very few (if any) semi auto guns that run at 500+ PSI that will get 1500+ shots out of a 68/45. Personally, I don't care about efficiency, even if I am playing outlaw. I don't shoot enough to care.

Regarding AKA valves and their springs, they are indeed pretty heavy, but they also use a pretty light hammer. The cupseal design does a lot of the heavy lifting. The large face helps it close faster. They tend to be really picky with springs rates, hammer weights, and volumes, though. If you don'y buy the full AKA hammer kit, and bolt, and have enough volume, you're in for a rough time. I tend not to like them for that reason, even if they are among the absolute best when set up properly.

The reverse is true of Shocktech. They use a heavy hammer and lighter springs to get both very low pressure and very high efficiency. Not quite as impressive as AKA, but less finicky. Not my favorite lower tube kit, but the point is that you can get similar results using very different methods. I had a mini orracle than ran at ~220 PSI, without a volumizer, using a stupid light valve spring, medium-light hammer spring, and a light hammer. Planet Eclipse valve and bolt. It was a crazy gun.

So yeah, lots of different approaches, lots of different outcomes.

Regarding whether or not it's "worth it", that's up to you. If efficiency is your goal, I'd avoid the lazarus valve. Simply put it's not what it's made for. AKA would most likely give you better efficiency than whatever you hav, but like I said it will be tricky to set up. The other downside with AKA is that, since they use heavier springs, you'll end up with a higher cocking pressure. This will be rougher on paint, which at high speeds is less than ideal. I'd look at something like Shocktech or Planet Eclipse. Not as efficient, but easier to set up and lighter spring rates will probably work better at those high ROF. Course, PE stuff is crazy expensive these days.