Operating Pressure vs. Barrel Length

**ChucktheMAGician** · 03-30-2003, 09:37 PM

Sounds logical to me. I'm just waiting for the deep blue regulars to come and drop some science and equations on your theory to see how it turns up! Off topic but what reg(s) are you running on your cocker?

**ES13Raven** · 03-31-2003, 10:45 AM

Inline Reg

I am running an AA Messiah :)

Originally posted by AGD
60 psi for the mag and the impulse
95 pis for angel
45 for matrix
110 for autococker

The next question we need to ask is, how far down the barrel does the ball have to go before the pressure gets to low to do anything useful? That answer is 8-10 inches. We know this from looking at the graphs that our gun dyno puts out. If your peak pressure is higher, say over 100 psi you can get away with a shorter barrel, if it's lower then you need a longer barrel.
AGD uses the precise contour of the power tube tip to release air in a controlled manner behind the ball to limit peak pressures to around 60-80 psi. So as far as our guns are concerned, the best efficiency would be had with an 8-10" effective length barrel.

So if 60-80 psi is the pressure coming out of the bolt on a mag, and 8-10" effective barrel length gets the best efficiency, the effective barrel length should be shorter for a cocker's 110psi right?

I assume the 110psi for a cocker is based on a stock cocker's operating psi? (350-450psi)

What about a cocker that has an operating pressure of 250psi? The pressure is lower, and dwell is longer so is the pressure coming out of the bolt closer to the Mag and Impulse?

A couple of other quotes I found interesting:

Originally posted by athomas
The barrel length is also a larger factor in lower pressure guns because the pressure is maintained for a longer period in order to allow slower acceleration to the desired fps setting.

A short barrel would be extremely inefficient on a low pressure gun. It takes a certain amout of torque to accelerate a ball to the desired speed. If the pressure is lower the rate of acceleration is lower. Therefore it takes the ball longer to reach the desired speed. In a short barrel, the distance is not there to allow that to happen. Therefore the pressure must be increased to allow a greater acceleration.

Originally posted by Paladin
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.

Comments?

**Mr Orange** · 03-31-2003, 03:33 PM

Here is how I understand pressure. 250psi at 295 fps or 320psi at 295fps makes no difference at all. Once the ball leaves the barrel (or reaches porting) acceleration is ceased. so the very instant the ball leaves the BBL it is slowing down wether it started slowing in the barrel (say the last 2 or 3 inches after porting) or it is slowing once it leaves so long as it is actually measured at 295 fps the only things affecting the speed/distance now are atmospheric variances. Assuming they are the same then it shouldn't make a difference.

Hope this helps, If I didn't make it clear enough, post again and I will try to explain my self better.

PEACE
LT

**ES13Raven** · 03-31-2003, 03:52 PM

Well.... what I want to do is find the best operating pressure for my Cocker with a 14" barrel.

I want to have the operating pressure be efficient for the barrel length, and have the velocity peak near the end of the barrel like Glenn suggests.

**ES13Raven** · 03-31-2003, 04:10 PM

Originally posted by Mr Orange
Once the ball leaves the barrel (or reaches porting) acceleration is ceased.

Does it really cease at the porting, or is that the point where it takes a dramatic slowing?

So if I have a Freak barrel, and acceleration ceases at the step or porting, shouldn't I get the same velocity with the tip off?

Does that really happen though?

**AGD** · 03-31-2003, 04:30 PM

So why do you think input pressure has anything to do with the pressure behind the ball? You should look at the data thread carefully.

AGD

**ES13Raven** · 03-31-2003, 04:39 PM

Originally posted by AGD
So why do you think input pressure has anything to do with the pressure behind the ball? You should look at the data thread carefully.

So are you saying that all Autocockers have 110psi coming out of the bolt regardless of the operating pressure, valve dwell, and bolt type?

**Redkey** · 03-31-2003, 06:35 PM

without putting words in his mouth...

I think he is saying that alot can happen between the pressure gauge reporting 250 or 320 and the face of the bolt where the air blast hits the ball.

Every inch of hose, connector, elbow and orifice will change the rate of air flow and therefore change the pressure at the bolt face.

What are the main goals of optimizing the air pressure?

higher shot count? more consistant velocity? better accuracy? less noise? higher ROF?

Since your cocker is probably different from all the others out there I doubt you'll get the correct answer from this or any other forum. You'll have to determine the pressure that best fits your barrel length, barrel diameter, paint diameter, paint weight, valve type, valve spring rates, hammer spring rate, hammer weight, tank reg flow rate, temperature, humidity... etc. on your own. Once you've found this pressure through extensive testing... don't change anything on your marker or you might have to start all over.

**ES13Raven** · 04-01-2003, 11:43 AM

Originally posted by Redkey
What are the main goals of optimizing the air pressure?

higher shot count? more consistant velocity? better accuracy? less noise? higher ROF?

I know that the 320psi input pressure will get better efficiency, but that is not what I am after. I'd rather have a quieter marker at 250psi, than a louder one at 320psi and get 50 more shots out of it.

I know I won't get higher ROF by doing this, and the more consistant velocity/better accuracy is questionable.

I'm thinking that the 250psi operting pressure is allowing the paintball to reach peak velocity more towards the end of the 14" barrel.

Is Glenn wrong when he said this?:

Originally posted by Paladin
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.

**athomas** · 04-01-2003, 03:02 PM

As mentioned earlier in this thread, a lot depends on the flow path between the input and the breach. The more efficient the flow path is, the more quickly the air is delivered. When the air is delivered in a more timely manner, the effect is that the pressure drop from input to breach is less. Therefore, the behind the ball pressure is more stable and controllable.

Most inefficient designs start with a high behind the ball peak pressure that quickly falls off due to flow restrictions. Many try to compensate using larger reservoirs to deliver a longer, lower pressure air blast. This is where the inefficiencies of low pressure guns comes from.

A lot of efficient guns are high pressure but have low behind the ball pressures. This is due to flow restrictions but is in part overcome by the higher input pressure which allows a consistent behind the ball pressure to be maintained longer.

The best design would use a fairly small volume of low pressure air, but would deliver it all at once. This scenario doesn't exist but many guns have gotten pretty efficient. Several of the cockers operate on very low pressure and do deliver fairly efficient operation as do many other brands as well.

Once you have the operational flow paths of the gun maximized, you select a barrel and then you tune your gun to match the operation that you wish to get. Ideally you should be able to get good efficiency and low noise. The efficiency will be directly related to the sustained behind the ball pressure and barrel length.

No matter what gun you have, you need a barrel that will maximize the acceleration profile you are providing. Otherwise, you will decrease the efficiency. The only way to know this is to try different combinations and settings. Find one that works for you.

If you are using a stepped, vented barrel, then the amount of acceleration past the porting is diminished. The stepped tip of the barrel only acts as a guide. The velocity of the ball at this time is probably only being maintained by the momentum of the air following it, or may even be slowing down. At any rate, the chrono reading you get is the true measure of consistency. No matter what anyone says. If the marker is shooting at 295fps, the ball will go as far as any other marker shooting at 295fps regardless of the acceleration or slowing in the barrel. At any given time once the ball has left the barrel, the frictional and gravitational forces are the same for all balls which are equal (ie; same brand, size and weight). Therefore they will slow down and fall at the same rate.

**Cristobal** · 04-01-2003, 04:58 PM

Things to ponder with how much pressure you need. - Automags.Org Online Forums

http://www.automags.org/forums/showthread.php?s=&threadid=18939