Barrel Length vs. FPS question

11326 Views 8 Replies 6 Participants Last post by The Chrome Avenger, May 12, 2012

chachaseeds

Discussion Starter · Apr 18, 2012

How will barrel length affect fps in bolt action rifles? I know in aegs, a full size (non-ported) cylinder will achieve the best fps with a ~480mm barrel. But what is the optimum barrel length (regarding fps) for snipers (VSR10 and APS2)? Because bb weight and spring power will also affect barrel lengths' relation to fps, lets just say that a 500 fps (w/.2g bbs) gun is shooting .36g bbs. Also, does having a longer barrel and a larger cylinder help when shooting relatively heavy bbs? Does anyone have any data regarding barrel length vs. fps? Thanks!

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MiloXC3

· #2 · Apr 18, 2012

I know that about 430mm is the perfect length for Type-10 platform rifles.
Have a look into the barrel-suck myth if you haven't heard of it already.
The diameter of the barrel will affect the fps lots more than the barrel length though.

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wyvernfist

· #3 · Apr 18, 2012

MiloXC3 said:
Have a look into the barrel-suck myth if you haven't heard of it already.
The diameter of the barrel will affect the fps lots more than the barrel length though.

Though the barrel-suck has been dis-proven, having more barrel volume than your cylinder volume can handle will create a drop in FPS.

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SilentScope

· #4 · Apr 18, 2012 (Edited)

How will barrel length affect fps in bolt action rifles?

Barrel length can increase or decrease FPS depending on your cylinder volume and air compression efficiency. Assuming very good air compression efficiency, you should focus on calculating your cylinder volume to barrel volume ratio which would involve math. I was actually involved in a thread not too long ago so I will refrain from re-posting the conversation here. This thread was originally posted no longer than 4-6 weeks ago. Search and you will find them.

But what is the optimum barrel length (regarding fps) for snipers (VSR10 and APS2)?

Your question about optimal barrel length can be better answered if you can give your personal definition of "optimal" in these contexts.

Also, does having a longer barrel and a larger cylinder help when shooting relatively heavy bbs

What do you mean by "help"?

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MiloXC3

· #5 · Apr 18, 2012

Sorry Wyvernfirst, that's what I meant.

I think by help, he means 'will it perform better'.

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The Chrome Avenger

· #6 · May 12, 2012

I have a complete laylax tuned TM vsr10 Gspec and here is what I have found out from my own experiences.
My G spec chronos at about 495fps to 500fps with hop set to about 1/4 using a .2g BB. Now if I chrono the gun with MADBULL ultimate heavy .36g it will chrono at about 425 to 430 fps. Now this means that my rifle produces about 3.06 joules of energy using the .36g BB, and if you work the figures out then my rifle should chrono about 560 fps with a .2g BB. I beleive that the lighter BB the .2g is out of the barrel before it uses the full acceleration of the piston and all the air, hence a lot of energy is wasted. Through using the heavier bb it is using more of the air from the piston and cylinder and is more efficient.
I have just purchased a new TB barrel 430mm and I am going to fit this to see what results I get using the exact same set up with a longer barrel, as i am very interest to see which set up is better.
As people have stated optimuim barrel length is do to do with cylinder air volume and barrel air volume.
(pi x radius squared x length) will give the volume of a cylinder and a barrel.
Then you need to work out the correct ratio.
Note tight barrels give more fps but may not be more accurate over distance and my advice would be don't worry about fps worry about consistant shots, a well set hop up will do wonders.

My current rifle set up is
Laylax zero trigger and piston.
laylax teflon cylinder.
Laylax Ball bearing spring guide.
Laylax 170 spring (clipped)
Laylax 303mm barrel. soon to be swapped for the 430mm.
Firefly Hard hop up rubber.
Dangerwerx hop up arm.
PDI receiver and outer barrel.

Hope this kind of helps.

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WorstInFinlanD

· #7 · May 12, 2012

That's a well known fact.

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SilentScope

· #8 · May 12, 2012

I beleive that the lighter BB the .2g is out of the barrel before it uses the full acceleration of the piston and all the air, hence a lot of energy is wasted. Through using the heavier bb it is using more of the air from the piston and cylinder and is more efficient.

You are mostly correct. This is actually what most people believe and have been spreading as truth. Aside from that, most people leave out a very important component- mass.

E= 1/2m*v^2

A heavy BB carries more energy at the muzzle because the heavier weight embarks less air resistance and more momentum as soon as the BB starts to move.

Lighter BBs slow down quicker/more than heavier BBs so this correlates to lower chronograph readings than what is mathematically expected.

If it were possible to chrono a 0.2g and a 0.36g BB perhaps 1/10th of the way in the inner barrel as it's being shot, the energy readings would probably be much closer than the moment it exits the muzzle.

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The Chrome Avenger

· #9 · May 12, 2012

Couldn't agree more silent scope, this is why I only use heavy ammo, lightweight ammo is a no no in my opinion in a heavily tuned vsr, the better results come from the heavy ammo. The heavy ammo carries a larger amount of kinetic energy and in doing so they hit harder, and are obviously less affected by wind etc.

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