Barrel suck nay or yea?

damagegt

Im planning of extending the length of the barrel in my type 56 by 4" and iv read in places that ill be affected by barrel suck but iv also read this its total bs.Any Ideas?

Since the cylinder in my gun is designed for a 455mm barrel will I need to change it to use a 550mm barrel?

DeBurca

Is the current cylinder vented if it is then yes you should change it for a solid or non vented type A

damagegt

cheers DeBurca.No my cylinder is solid.Would i be alright or would I need a bore up kit?This is what im basing it off,well some of the maths are off but ull get an idea.

Quote :

So ’ve been looking at the whole Barrel Suck phenomenon and I just can not accept it as given.
I needed proof. So I decided to formulate some calculations as a starting point.

I’ll cover a lot more in this post, so please read through it fully before posting knee jerk reactions to my hypothesis.

For the purpose of this, I need to clarify some terms. Most will know them, but just in case…

Definitions;

AEG: Automatic Electric Gun (airsoft)

Barrel Suck: The phenomenon that apparently occurs when an AEG piston begins retracting while a BB is still in the barrel, causing a loss in FPS due to the piston sucking back air from the barrel behind the BB.

FPS: Feet per Second – Velocity of the airsoft projectile

IPS: Inches per Second (FPS X 12) used for calculations within this hypothesis.

ROF: Cyclic rate of fire measured in Rounds per Second or RPS

My hypothesis:
Barrel Suck is a misnomer perpetrated on the Airsoft Community at large due in large part to certain active persons in forums across the world coining the buzz phrase with little more than speculation and guesswork and a great degree of “Technical Gobbledegook” to fool the masses into a perpetual belief that what they say must be true.


Here are some mathematical statistics and formulas that can be duplicated to match any guns specific performance values. This is assuming the AEG is in prime operating condition and NOT double feeding due to magazine or hop-up issues.


Test Bed #1 (Long barrel, Low FPS, High ROF):

Inner Barrel Length : 600mm (600mm X 0.03937 = 23.622 in, but let’s call it 24”)

FPS: 250 (about the lowest FPS for a decent gun)

Cyclic Rate: 20 RPS

Calculations:
At 250 FPS, it takes a BB 0.008 seconds to travel 2 feet (24”, or just over 600mm).
[1 second, divided by 250 feet, times 2 feet]

At 20 RPS, a BB is fired once every .05 seconds.
[1 second divided by 20]

Assuming Zero Point on our timeline to be the point where the piston releases from the sector gear, the BB exits the barrel at approximately 0.008 seconds, leaving 0.042 seconds before the next shot even begins to travel down the barrel.
[0.05 minus 0.008]

The BB is only in the barrel for the first 16% of the firing cycle.


Test Bed #2 (Long barrel, High FPS, Moderate ROF):

Inner Barrel Length : 600mm (600mm X 0.03937 = 23.622 in, but let’s call it 24”)

FPS: 400 (the golden number for many)

Cyclic Rate: 15 RPS

Calculations:
At 400 FPS, it takes a BB 0.005 seconds to travel 2 feet (24”, or just over 600mm).
[1 second, divided by 400 feet, times 2 feet]

At 15 RPS, a BB is fired once every .066 seconds.
[1 second divided by 15]

At Zero Point (piston release), the BB exits the barrel at approximately 0.005 seconds, leaving 0.061 seconds before the next shot even begins to travel down the barrel.
[0.066 minus 0.005]

The BB is only in the barrel for the first 7.5% of the firing cycle.


Test Bed #3 (Average barrel, Average FPS, Moderate ROF):

Inner Barrel Length : 363mm (363mm X 0.03937 = 14.29 in, but let’s call it 14.5”)

FPS: 350 (pretty standard for non TM stock guns)

Cyclic Rate: 15 RPS

Calculations:
At 350 FPS, it takes a BB 0.0035 seconds to travel 14.5 inches.
[1 second, divided by 4200 IPS (350 FPS X 12), times 14.5]

At 15 RPS, a BB is fired once every .066 seconds.
[1 second divided by 15]

At Zero Point (piston release), the BB exits the barrel at approximately 0.0035 seconds, leaving 0.0625 seconds before the next shot even begins to travel down the barrel.
[0.066 minus 0.0035]

The BB is only in the barrel for the first 5.3% of the firing cycle.

Based on these examples, anywhere from 84 to 94.7% of the time (while the gears are spinning) there is nothing going down the barrel!



Also busting this “Barrel Suck” myth is the actual function of the AEG gearbox..

Before the sector gear teeth can even engage the piston teeth, the tappet plate is disengaging the nozzle from the hop-up chamber thanks to the ingenious location of the tappet nub.
While the piston is retracting, it will draw air through the nozzle, but since the nozzle is no longer sealed within the hop-up chamber, it can not suck air from the barrel. Try sucking soda through a straw with the straw opening just millimeters outside of the liquid. All you’ll get is air. Your sucking has no affect on the soda, just like the piston has no affect on the BB in the barrel (if it’s even still IN the barrel).



Now, with all of that being said, there is a problem which occurs with improper cylinder sizing which will affect FPS, Accuracy, Consistency, and Performance.

This problem occurs when your cylinder does not physically have enough air volume to fully propel a projectile down the entire length of the barrel.

Typically, cylinders have venting holes at certain positions along the length of the body. This is primarily to minimize air resistance during piston acceleration after release in small to medium barrel lengths. There are many resources available to guide you to the proper cylinder type for your barrel length.

Putting a 500mm long barrel in a gun with a cylinder designed for a 363mm barrel is looking for trouble. Your cylinder will not have the sufficient air volume to propel the projectile down the entire length of the barrel.

Use the following formula:

Cylinder ID in mm X Cylinder ID in mm X 3.1415 (Pi) X Cylinder length in mm (to hole, if it has one) = Cylinder Volume in Cu mm

Barrel ID in mm (if you don’t know the ID, use 6.08) X Barrel ID in mm X 3.1415 (Pi) X Barrel Length in mm = Barrel Volume in Cu mm
If your Cylinder Volume exceeds your Barrel Volume, you’re good to go.
If it’s close, you may want to move to a Zero or Bore Up cylinder.


So, in closing, the phenomenon known as “Barrel Suck” has absolutely nothing to do with barrel suck. It is simply a result of improper sizing of cylinder type to barrel length.

PS Ill be home tomorrow and Ill let you know about the Ak.

DeBurca

You are correct when you say that cylinder needs to match the barrel length
For a BB to be expelled from the barrel, the swept volume of the cylinder should be equal to or slightly greater than the volume of the barrel
I would suggest that a greater volume is best as air is compressible and so having a slight excess is best

You made a basic mistake in your calculations about the length of time that the BB is in the barrel
You need to allow for the time it takes for the BB which at rest to accelerate to its exit velocity and there is the friction between BB and barrel wall, this is where TWIST barrels are supposed to come into their own

But yes if you have a solid cylinder than you should be good to go

damagegt

cheers again bud.Ill go try it out so.chat to you soon.

NakedDex

You should actually be fine. There's no hard and fast rule with combinations for barrel lengths in relation to cylinder volume because individual things like stroke lengths and spring characteristics all come into play, but taking the lead from Prometheus's cylinder sizings, you can get away with what you have. Their largest cylinder caters from 451-550mm, with the next size down being 401-450mm.
The difference cause by the "suck" theory is miniscule on the scale you'd be working on anyway, virtually unnoticeable.


But if you REALLY wanted to get anal about it, I can suggest a few methods to determine the approximate size you'd need. It means a whole bunch of maths and a vernier callipers though.
The alternative is, if you don't trust your cylinder, get that Prometheus one.

Don't go bore-up. If you do, you'll have to change everything else to match. Bore-up cylinders need bore-up heads and piston heads, bore-up airseals, etc. It's an unnecessary pain in the moobs. If you want to be frustrated and confused, get a Rubiks cube, it's cheaper.

Firekitten

Vented cylinders are fitted on shorter weapons, m4 or less, if youve got a solid, its fine. It will be good to about 550, though thats as far as I'd go. However, the real question here, is what good you think 4 inches will do? (not much really) A tightbore barrel and new hop would have far greater effect overall tbh, and be less cumbersome.

Love the calculations btw, facinating read, even if i am decafinated at the moment and groggy lol.

damagegt

Firekitten wrote: »

Vented cylinders are fitted on shorter weapons, m4 or less, if youve got a solid, its fine. It will be good to about 550, though thats as far as I'd go. However, the real question here, is what good you think 4 inches will do? (not much really) A tightbore barrel and new hop would have far greater effect overall tbh, and be less cumbersome.

Love the calculations btw, facinating read, even if i am decafinated at the moment and groggy lol.

well if I have the space in my pbs-1 and im getting a new barrel I might aswell get the extra 4",it wont do any harm.Cheers for the help guys/girls.

Firekitten

damagegt wrote: »

well if I have the space in my pbs-1 and im getting a new barrel I might aswell get the extra 4",it wont do any harm.Cheers for the help guys/girls.

but it can cause harm.... especially if its of no use. Plus have you seen how long pbs1's are? its nearly a foot long... on the END of your gun, and heavy :P you're gonna get pissed with that thing fast, and take it off... and oh, barrel too long.

damagegt

Ah its not that bad.Its only 8 inches and 290g. Im a big boy .But your right ill wait untill I see if ill like it and if not ill pass it on here and if I decided to keep it I can always try a barrel down the line .

Southern Dandy

if by some wierd reason there was airsoft porn the dialogue would be very similar to this post. all jokes aside very intuitive though.