Things to ponder with how much pressure you need.

[Ityl]

there would some force on the paintball after it leaves the barrel, but not a lot, so the more I think about it, the more I shoot down my idea, along with you guys said. Kind of like the idea of electricity travels the path of least resistance, but not totally, some always goes down the more resistant path.

And why would creating a vaccuum be a bad thing? couldn't you use it to your advantage by creating a vaccuum, then opening the bolt and let a rush of air down the barrel to aid efficiency? And it would pull the next ball into the chamber.

I want a gun dyno, I'd never be bored...lol.

[ShooterJM]

Originally posted by Ityl


I want a gun dyno, I'd never be bored...lol.

Boy I know that feeling.....and a wind tunnel!

[Mr. Grumble]

I need to visit Blue more often, this is great reading.

Seems to me that negative pressure would be difficult to achieve, with regularity, in a Mag. The open bolt blow forward would allow atmosphere to flood in through the breech in an attempt keep you at 0 psi. To reach negatives with any regularity you would need to fire from a closed bolt marker.

Now, if you had a long, un-ported barrel on a closed bolt marker you could generate a good sub-atmospheric pressure during firing. And if you cycled the bolt before the paintball were to exit the barrel (exposing the breech to the atmosphere), you would generate a sudden rush of atmosphere in through the breech. If a second paintball were waiting to drop into the breach, it would be exposed to disparate pressures. Therefore, atmospheric pressure would accelerate the paintball into the breach in addition to the acceleration of gravity.

Heaven help us, we have entered the Shadow Lands called 'ball suck'.

Mr. Grumble

[As a side note, what is the sound signature of a marker that fires at a negative psi like?]

[athomas]

As long as the ball is in the barrel of most paintball guns with a standard barrel length, there is pressure throughout the length of the barrel. If the bolt opens while that pressure is present it will flow up the feed tube. This is known as blowback.

Once the ball exits the barrel, the sudden gush of excess air out the barrel end creates a vaccuum effect which is the negative pressure which can be measured.

On most guns you can see this effect by dry firing them. Without the ball holding back the air, all the air gushes out the front of the barrel creating this vaccuum effect. Put a piece of tissue in the feed tube and dry fire the gun. It will suck the tissue into the barrel.

Autocockers are known for this effect because they are a closed bolt design and the bolt timing is such that it doesn't open until the ball has exited the barrel. If the timing is such that the bolt opens immediately after the ball exits the barrel, you will experience this vaccuum. Its kind of interesting.

There are exceptions to this rule because of different markers operating at different pressures and chamber volumes as well as barrel lengths and porting. These all affect the air movement and pressure within the barrel.

[Paladin]

Way over my head.

Hi guys,
I just had to put my two cents in here.

I was pretty good at math when I was a kid but it seems I've forgotten most of what I learned in basic hi school algebra 35+ years ago.:)
Back in the day when we only had 12 gram cartridges to work with, it was far more important that the gun be as efficient as possible than it is today with everyone using bulk tanks with either compressed air or CO2. I'm still a big fan of CO2 for paintguns because I could never find a real good reason to endure the costs, bulk and weight of the typical HPA system on mu gun.
All these numbers and calculations are great I guess but I never learned to use them effectively. However, I have learned some things from many years of testing and development work in the process of making paintguns as effective as possible. What I have learned from experience is that it takes X amount of energy to get a ball up to speed and there is only X amount of energy available in the supply tank, regardless of size or the type of gas in it.
The trick to an efficient paintgun is to deliver that energy to the ball under conditions that allow for a short burst of air that can run as freely as possible to push a ball to speed in the shortest distance possible and metered so that propulsion load ends at about the same time that the ball gets to desired speed; and that should happen just before the ball gets to the muzzle. Efficiency is determined by the metering process AND what happens after the air is dumped. Slight interuptions in the air flow between the valve and the back of the ball can make a big difference in how effectively the burst of air can impart it's energy to the ball. ie: A little trick that can easily pick up a few fps on an Amag is to streamline the back edges inside of the face of the face of the bolt with a Dremel tool. It will only add a couple fps to the chrono averages but every little bit helps. Generally speaking, as a paintgun gets more efficient, it also gets more accurate. This because an efficient shot generate less muzzle blast that could kick the ball off course.
In most cases, lower pressures do not necessarily mean better efficiency because we are dealing with a relatively fixed velocity limit. Lower pressures require slower operating speeds, extremely well tuned air passages between the valve and ball,longer barrels and generally cause more wasted gas/energy in the process of getting the ball up to speed.
I never know what the actual pressure stored in the valve chamber of a gun is until after I finsh getting it tuned for optimum performance. For most paintguns, somewhere around 400 to 450 psi HPA (a little less with CO2) seems to present the best acceleration characteristics and maximum efficiency for painballs at field speeds.
I'm sure some of you technical types will dissagree but I just wanted to point out that there is a great deal more to firing a paintgun "efficiently" than what you can figure out with a scientific calculator. What I've learned comes from about 18 years of a great deal of trial and error development work toward getting a paintball to go where and when I want it; And that started after about 25 years of working with firearms and balistics with the same goals in mind.

[AGD]

Welcome Glen! I told you that you would like this place!!

:)

AGD

[Vegeta]

Welcome to AO Mr. Palmer!

You'll love Deep Blue... I have been misproven many times by the people that post here. And it is very suprising to see all the math and physics being applied to paintball here... this is hands-on stuff.

I have been off this subject for a bit so I am going to read upwards a bit and then post my comments if I ahve any...

[Vegeta]

OK I read up a few posts and saw that some of you were talking about vacuums created by the ball travelling down the barrel. I first found this a few weeks after getting my first semi-auto, the good ole M98. Some people were talking about the blow-back and how if the air isn't vented properly, balls will get blow up the feed neck and will cuase feed problems at higher ROF's. I didn't get this totally, becuase the bolt was moving forward... and.. well.. I just had to see this for myself. I took a square of toilet paper and my 98 outside. gassed her up. I split the 2 plys in half and laid one sheet on top of the elbow, And fired the gun. I found that it sucked the paper into the tube a bit. Interesting.

If we could harness this power a bit more effeciently, maybe someday we could haev mroe effiecient feeding. Tippmann has already came out with their new air-powered ram agitaded hopper, based off the old F/A hopper design. We saw it a few months ago on Warpig as a prototype, and now it is going into production on the new Tippmann A-5, which is shipping in a few days (County Paintball took pre-orders).

But that is a bit off topic, and valves are my thing.. not feeding.

[cphilip]

Welcome Mr. palmer. We are very honored to have you here.

[Paladin]

Paintguns suck ??

First off, I want to thank you all for welcoming me here. As I said before, much of the discussion here is way over my head in terms of the "science" involved so I still have to operate on practical experience and a K.I.S.S. principle understanding of the launching of a paintball.
Question: If shooting a paintball can generate a vaccuum in the barrel, what does that tell us about what is actually going on ? What it tells me is that the gun is not tuned very well because peak velocity happened long before the ball got near the muzzle. Then when the propelling gas runs out of push, the ball has to carry the rest of the way down the barrel on energy alone, sucking wind behind it and loosing/wasting energy. If the ball starts decelerating while it is still in the barrel it can't keep up with,or carry as far as a ball that doesn't start decelerating until it leaves the barrel.

[FooTemps]

Wow Mr. Palmer... that made a lot of sense to me. I guess practicality always underlines brilliance. Good methods to work with in my opinion, how long did it take you to tune your paintball guns to have good efficiency and power?

By the way, WELCOME!

[Vegeta]

Wow, that did make alot of sense. If there was pressure from the gas behind the ball the entire way, then the ball wouldn't be sucking air. But it seems like the gun's valve gave a burst, then let off, leaving little force on the ball after it reaches a certain point in the barrel (porting might have a role in this.....). So... What we want is a steady stream of air behind the ball all the way down the barrel. We want it to be enough air to propell the ball fast enough (290 fps) but we also want to keep it rather low pressure for gas efficiency sakes. What if we had a valve that let out a slow, low pressure stream or air at first.. to get the ball going down hte barrl.. and then lets out a larger voulume shot of air after that, the keep built pressure and volume behind the ball. Its not just pressure on the ball that we want, beacue the ball is going down the barrel, the volume of the gas decreased, and the ball is having to pull the air behind it, cuasing that vacuum. So if we get a phhhhhhh of air followed directly by a pop of air, we will keep enough gas behind the ball, hopefully without being a gas hog. Not the first 'phhhh' of air wouldn't need to be very high presure, just enough to get the ball moving. But it would have to be held out a bit longer, so it maintains a presistant pressre/volume behind the ball. Then comes the higher pressure, but shorter burst of air, followed directly after the low low pressre stream. Keep in mind the ball is still in the barrel. The higher pressre, short burst of air will push all the air in the barrel with the ball out the barrel at 290 fps. Whew.

Did you guys understand that? It would take a very, very comeplex valve to test that theory out, and after all, it is just a theory. I don't think such a thing would be produceable via a mag valve... a complex poppet valve maybe.
I'll think on that one. First, you guys see if that makes sense to you.

[Paladin]

Getting it to work.

Tom,
You were quite right. I do like it here. Very interesting group, to say the least.

Some ??? to AGD,
Given a standard production AutoMag on compressed air, "average" humidity and barometric pressure, decent paint, etc. How far from the face of the bolt will the ball travel to reach 300 fps ? and how far... to reach say 270 fps ? Now, same scenario but with CO2?

FooTemps,
It took me several months after I got my first two paintguns to get a handle on making my equipment as effective as possible. On my 3rd time out to the local "Survival Game" field I bought one each of the two guns that were available at the time in order to see which I could get the most out of for my game. (a Nelspot 007 and a Sheridan PG; PG = forerunner of the PGP; no pump handle)Anyway, with my gunsmithing background it was real easy to figure out just how they worked but figuring out how to make them work better was a different matter. My game skills developed rapidly but my equipment was keeping me from excelling. Too old to out-run 'em, so I had to out-gun 'em to get to the flag.
Accuracy of course was an issue and the first thing I did to both guns was polish the barrel; however, efficiency was of greater concern. Paintballs then cost $2.50 for a 10 round tube ($.25 each). A 12 gram cartridge was a buck and you could get about 10-12 shots out of a cartridge. I hated wasting money but it was more important to gain a tactical advantage in the game by lowering the frequency of maximum vulnerability when you run out of gas and had to change cartridges; which at that time was about a 30 second process. (An issue that I resolved a short time later)The idea being to run 'em out of gas and rush 'em while they change cartridges.
I knew how to optimize the internal ballistics in firearms but this was going to take a whole new line of thinking. The first step was numerous trips to the library to gain an understanding of CO2. Then, basic air flow and fluid dynamics concepts were explored. Leading me to the conclusion that I had to meter the release from the valve effectively and then let my paintgun "breath" freely. Armed with a new load of relevant information, a little common sense, a garage full of tools and a huge determination to have better equipment, I went to tinkering and testing the results of every little thing I did. I also had a chronograph to work with. A chrono wasn't part of the game yet but it proved invaluable in determining if any changes I made had positive results. Certainly better/cheaper than counting shots per cartridge. Quite simply, if I made a change and the velocity went up, I was headed in the right direction. If the velocity didn't change I could move onto another detail but if it went down I had to back up and figure out why; undo it and then move on. I was able to double the efficiency of my paintguns pretty easily and eventually got to nearly triple the "good" shots from a cartridge over stock configurations but that was a long winded process. Well worth the effort though as it created some major advantages on the field. It turned out that I was able to get better overall effectiveness out of the Sheridan valving format than I could get with the Nelson system so I stuck with the Sheridan. Along the way, we got pump handles, gravity/direct feed and I came up with a quick change unit for the 12 grams (QuikSilver)which gave me the firepower of "constant air" a bit before bulk tanks were even introduced. But that is another story.:) Palmer's Pursuit Shop came to exist largely because many people asked: "What would you charge me to do my gun like that?"
Sorry for rambling:
Take care all.
Later
Glenn

[Vegeta]

Yep.. paint cost $2.50 for a 10 round tube and we had to walk 25 miles uphill in the snow to get em!


People complain about prices of paint nowdays... of course demand went up greatly when semi-auto markers came out... but thats another topic.

[FatMan]

Sucking feed tubes

Hey all.

Not to disagree with Glenn (who is one of my heros - I used to own Typhoon BB9) but slight suction at the feed tube does not neccesarily mean there is vacuum in the barrel. The air blasting down the barrel AFTER the ball is expelled will cause some draw at the feed tube - unless the chamber remains closed well after the shot (like in a closed bolt system). In fact, air blasting *past* the feed tube can cause suction, the same way the wind blowing past a chimney causes a draw that pulls the smoke out.

If your paintgun is running out of air well before the ball leaves the barrel, something is wrong!

All that said, Glenn is certainly right on with what he's saying. All of the equations are just rought approximations of what's really going on. There are just too many inter-dependent variables to do a decent analytical job with this. More is to be gained through working with the system as a whole - and I think Tom and Glenn are two of the most experienced at this - which is why they make the best paintguns in the world.

FatMan