Blowback vs Blow Forward

[Cornmuffin87]

okay, this is not which is better, blow back or blow forward, i want to know, since in a blow forward system co2 or nitro is only being used forward instead of both ways to recock the bolt, do mags use less co2/nitro than, lets say a Custom 98 or other blow backs?

[BajaBoy]

Uh blow f uses more i think

[automan39]

the air in a blowback is used after blowing it back to also blow it forward. Blowforwards (ie mags) r more consistent velosity wise and r nicer guns overall.

[puckmaster]

I think the mag would use less because on a blowback and a blowforward, the air is vented in the last stage(or second to last with the blowback).With the blowback, it is oporated by the mainspring and would have crappy consistintsy(shooting hot once in a while) then you have the mag, with air is vented when air pushes the bolt to a position where it will vent.

[puckmaster]

I just read that and realized that it looks like CRAP. anyone want to reword it?

[mike e]

not sure on air consumption...my guess is this, over all a blow back maybe more shot for shot consistent, but a mag may use the air it takes in more efficiently. its really hard to compare though because a lot of effiency is based on the valve, so i really am just taking a stab in the dark here. i wouldnt even know how to compare them fairly. anywho, both setups have their advantages and disadvantages, but to be honest the thing that drew me most to the mag was the single tube design. sounds stupid i know but i got board with the shoebox on a grip frame design

[PyRo]

Blow foward would use less. IN a mag you have the bolt, with air lets say 200psi (used for referance not actuall number) behind it, being held by the sear. In front of the bolt you have the bolt spring. Now, the trigger is pulled. The bolt travels foward due to the air behind it compressing the spring. Once the bolt gets all the way or almost all the way forward, it releases the air into the barrel. The spring then pushes the bolt back, and its ready to do again. So the mag is recocking itself with the same air that is being used to acclerate the paintball. With a blowback, differant air is used, and wasted.

[athomas]

Most blowback guns have a high pressure in the chamber waiting to be released (even higher than a mag). Actually, most blowback guns use the pressure that is available from the bottle, which is usually about 850psi. Mags are regulated so the chamber is about 350-400psi.

The higher the chamber pressure is, the better chance you have of obtaining greater gas efficiency. Blowback gas is vented and wasted once the cycle is complete, but the higher efficiency due to higher operating pressure means the gun is still fairly gas efficent.

Mags are designed to use all the gas that is used in the chamber. The same gas that is used to push the bolt forward is also used to fire the ball. This is very efficient design. However, because it uses a lower chamber pressure, it loses some of that efficiency. If the chamber pressure were further reduced, the mag efficiency would go down the tube. On the other hand, if the pressure were increased (chamber volume decreased), the efficency would go up, but it would be harder on balls.

The design of the mag definately makes it the more consistent marker.

[PyRo]

I don't think it would make a differance if it were HP or LP. It still takes teh same amount of air to fire the ball correct? For exapmple if you have a 1ci chamber at 400psi isn't it the same thing os a 2ci chamber at 200psi? If you use higher pressure you decrease the chamber size, however there is more gas in that small chamber. If you use a lower pressure, you increase the chamber size, but you decrease the pressure. Hence your going to use about the same amount of gas regardless of HP or LP. Because you will always need the same amount of gas to move the paintball nomatter what form its in.

[athomas]

The lower pressure air chamber has less acceleration and therefore needs air to remain pressurized over a longer period to reach a desired velocity. It actually takes more air at a lower pressure compared to a higher pressure because of this.

Think of this exagerated example. How much air would it take to reach 300fps at 10 psi. It would take a lot. It could probably be done if the barrel was very long and the pressure could be maintained in the barrel, but it wouldn't be very efficient or effective.

[Rambozo]

Originally posted by athomas
The lower pressure air chamber has less acceleration and therefore needs air to remain pressurized over a longer period to reach a desired velocity. It actually takes more air at a lower pressure compared to a higher pressure because of this.

Think of this exagerated example. How much air would it take to reach 300fps at 10 psi. It would take a lot. It could probably be done if the barrel was very long and the pressure could be maintained in the barrel, but it wouldn't be very efficient or effective.

I really dont think this analogy applies towards the pressure or volume of gas in the gas chamber. But towards the gas directly behind the projectile. Pressure directly behind the projectile is NOT equal to the gas pressure in the gas chamber. Look here (http://www.automags.org/resource/tech/tomstech/01_barrel_eff.shtml) for more info on what Im talking about.

And also remember that a 68ci container @ 4000psi contains no more/less gas than a 34ci container @ 8000 psi.

So its not fair to simply say lp decreases effiency without first considering the other factors like valving, barrel length, and chamber size, along with operating pressure.

The only benefit I could see to running a certain pressure would be the effects it has on a regulators ability to regulate. And this is information I do not have access to.

[athomas]

I had a lovely explaination last night that took about 1/2 hour to type. That was right before I accidently bumped the on/off switch on my computer and lost everything. Doh! LOL.

I'll try to sum it up again if I can.

Talking about mags only here:

A small, high pressure chamber would provide a large pressure differential between the chamber and the barrel area behind the ball. The gun when fired would cause the pressure to spike at 60psi before the ball starts moving. As the ball moves away from the bolt, the volume of the barrel behind the ball gets larger faster than the chamber can release air to maintain pressure. The rate of acceleration is high at first trailing off to less as the ball moves down the barrel. Once the pressure behind the ball is less than the frictional forces opposing the ball, the ball starts to slow down. This should happen at the end of the barrel for maximum efficiency.

A larger, low pressure chamber would provide a smaller pressure differential between the chamber and the barrel area behind the ball. The gun when fired would cause the pressure to spike at less than 60psi before the ball starts moving. The reason would be because the rate of discharge from the chamber to the ball would be less due to the lower pressure differential. Meanwhile, the ball would begin accelerating away from the bolt face, thus making he volume behind the ball ever increasing. The lower initial pressure would cause a lower rate of acceleration on the ball. That would mean the ball would have to accelerate longer to reach the desired velocity. The pressure of the volume behind the ball would have to have to be maintained longer to provide this acceleration. At the point where the pressure in the barrel and the frictional forces opposing the acceleration are equal, the barrel should end. This will be at a point farther away (longer barrel) from the bolt face than the higher pressure scenario. Therefore since the forces are equal at the same velocity(300fps), the pressure in the barrel must also be equal, therefore the amount of residual air in the barrel will be greater for the longer lower pressure system. This residual pressure is wasted out the end of the barrel. Plus, the longer the barrel, the more friction there is exerted on the sides of the ball for a longer period of time. Friction also contributes to inefficiencies.


I must conclude that the lower pressure valve in the mags case, would be less efficient.

That may not be the case in other designs. The ability of the valve to deliver air to the volume area behind the ball affects the efficiency. If a gun could operate at 200psi and effectively deliver the 60psi pressure spike behind the ball, it would achieve the same efficiency results or possibly better or worse depending on other factors.

[athomas]

Originally posted by Rambozo

And also remember that a 68ci container @ 4000psi contains no more/less gas than a 34ci container @ 8000 psi.


Yes these contain the same air/gas but they are regulated at a fixed psi say 800psi. The 800 psi is the pressure that the mag or any gun sees, not the pressure in the bottle.

In the valve of a mag, we are talking about changing the chamber pressure. We have no way of accurately regulating the pressure from the chamber to the front of the bolt(behind the ball). If we could guarantee the same pressure behind the ball at different pressures in the chamber, then you would be correct.

[Rambozo]

Originally posted by athomas


Yes these contain the same air/gas but they are regulated at a fixed psi say 800psi. The 800 psi is the pressure that the mag or any gun sees, not the pressure in the bottle.

In the valve of a mag, we are talking about changing the chamber pressure. We have no way of accurately regulating the pressure from the chamber to the front of the bolt(behind the ball). If we could guarantee the same pressure behind the ball at different pressures in the chamber, then you would be correct.

I wasnt refering to the gas/air in the tank alone. This still applies to the gas in the airchamber of the gun.

Now the valve acts as a bottle neck. In the case of the mag Im talking about the bolt assembly. This acts as the valve between the air chamber and the rear of the projectile. So changing the degree of the bottle neck will change the initial pressure behind the projectile. In this case there is little you can do to change it. aside from changing the bolt spring, or bolt mass. But even if you was to reduce the pressure in the mag you still wouldnt suffer in efficiency because only the gas in the chamber is expelled(this is where that "And also remember that a 68ci container @ 4000psi contains no more/less gas than a 34ci container @ 8000 psi." jargin comes into play.). The only thing that would suffer is velocity. But we are not just talking about the mag. We are talking about guns in general. Other designs are a bit more flexible when it comes to valving.

The point is that if the valve is in tune with the operating pressure of the gun, then there should be little to no difference in efficiency reguardless of the operating pressure.

In your previous post you said "The higher the chamber pressure is, the better chance you have of obtaining greater gas efficiency...". Which I find to be a bit inaccurate.


Uh well had I completely read your previous post, then I might have realized that we are for the most part in agreement with each other. But there you go my incoherent rambling anyway.

[PyRo]

Blow back uses more.