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Old 04-20-2017, 10:00 PM   #1
Young Gun
 
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Ideal Cylinder/Barrel Ration to BB weight

Hi All! First post after intro! I've been lurking for a while, on many forums really, and came across 1tonne's information from his extensive testing on cylinder/barrel ratios with reference to bb weights, with his permission. For anyone looking for the information I based this on: Choosing a heavy-weight bb

I noticed a bit of a curve in the changes between bb weights and ratios, and assumed, probably naively, that some form of relation could be extrapolated. After a few hours or research, a slight refresher in college level algebra, and some excel tutorials, I came up with an equation and graph. Theoretically, these would provide individuals with the greatest efficiency and joule creep at the given weights.

The equation is Cylinder:Barrel=(7.5*(weight of the bb in grams^2))+1.55

The information on the left is the theoretical weight of the bb and the associated derived ratio. The highlighted information are the weights used by 1tonne in his information. The hightlighted information on the right is 1tonne's information.



I provided the data from the non-1tonne points as theoretical bb weights, increasing from .2g to 1g in .01g increments. In theory this should provide a relative guide as to the ratio required of any weight of bb within the provided weights, and remove the guesswork associated with it. As a general disclaimer, this is based on 1tonne's numbers and probably not strictly an exact fit, especially considering I extrapolated this visually and not mathematically or statistically. I would personally guess these to be at most 10% off of the theoretical ideal ratio, but if I'm totally off base for any reason, please don't hesitate to comment, critique, adjust, or otherwise provide feedback!
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Old 04-21-2017, 03:54 AM   #2
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I believe there was already an equation for this, but it was way off. Yours seems pretty on point

For VSRs, this formula should more or less be accurate :)
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Old 04-21-2017, 11:41 AM   #3
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Thanks for the feedback! As this was my first foray after a lot of lurking I hoped it would go well and am glad to have positive feedback! Thanks
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Old 04-25-2017, 01:08 AM   #4
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A question.....how does low power affect the ratio?
In Japan I am limited to .96j for field use
Built 3 vsr's but still learning but test fired 1000's of rounds trying combinations of bb weights barrels , cylinders , pistons and springs
The perfect ratio allows the greatest possible performance ....right?

I read in 1 tonne's guide to use 554mm barrels , but I started cutting it in my early experiments

Sorry not a math guy
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Old 04-25-2017, 02:03 AM   #5
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Quote:
A question.....how does low power affect the ratio?
My current hypothesis is that it doesn't matter, but I aim to test this sometime soon along with several other variables. As soon as I have time, that is, currently working 12hrs a day

If anyone else has data though, consider me interested... :)
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Old 04-25-2017, 02:31 AM   #6
Rvl   Rvl is offline
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2.92:1 is the ratio for 430mm
What is the ratio for 303mm?

All my experiments have been with 303 so far
But will begin building a 430mm tonight
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Old 04-25-2017, 10:06 AM   #7
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Yesterday I did some tests with 0.2g 0.25g 0.28g and 0.36g bbs on stock Tokyo Marui vsr-10. I'll post resoluts later as I'm away from home right now but from what I can remember the joule reading was highest with .28g bbs.
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Old 04-25-2017, 02:09 PM   #8
Skurzef   Skurzef is offline
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Stock TM vsr-10 pro sniper
0.20g - 308fps - 0.885j
0.25g - 280fps - 0.925j
0.28g - 267fps - 0.932j
0.36g - 232fps - 0.914j
0.43g - 211fps - 0.912j

I don't know if it proofs anything but I hope it'll be helpful :p
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Old 04-25-2017, 02:14 PM   #9
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Quote:
Originally Posted by Skurzef View Post
Stock TM vsr-10 pro sniper
0.20g - 308fps - 0.885j
0.25g - 280fps - 0.925j
0.28g - 267fps - 0.932j
0.36g - 232fps - 0.914j
0.43g - 211fps - 0.912j

I don't know if it proofs anything but I hope it'll be helpful :p
It shows that .28 BBs are more ideal than .36 since losing joule means your undervolumed
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Old 04-25-2017, 02:27 PM   #10
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I wonder how it'd behave with higher fps and without airbreak since 430 barrel is said to perform the best with 0.36-0.4g bbs
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Old 04-25-2017, 04:24 PM   #11
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430mm barrel performs best with 0.43gm bb's. Not 0.36-0.4gm although they will still be ok.
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Old 04-25-2017, 05:37 PM   #12
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Wow! didn't realize a few days away and it'd kinda blow up!
Quote:
Built 3 vsr's but still learning but test fired 1000's of rounds trying combinations of bb weights barrels , cylinders , pistons and springs
The perfect ratio allows the greatest possible performance ....right
Rvl, honestly, the other members who have more experience are going to be more help with the limiting of the joule energy. I intended this strictly as an mathematical analysis of the numbers that 1tonne put up. In theory, yes, the given ratios of the cylinder to the barrel should provide the greatest efficiency for the BB weight regardless of fps. Also understand that these ratios are based on BB weight. So to use this effectively, I would personally either go from the cylinder forward or the bb backwards.

Eg. I have a cylinder of 'x' volume, and I have a barrel volume of 'y'. The ratio of x:y provides me with the most efficient bb for my current set up.

Or

I have 'a' bb's. These would be best used with 'b' ratio. I can then alter my ratio of cylinder and barrel volume to best utilize these bb's.

Quote:
Yesterday I did some tests with 0.2g 0.25g 0.28g and 0.36g bbs on stock Tokyo Marui vsr-10. I'll post resoluts later as I'm away from home right now but from what I can remember the joule reading was highest with .28g bbs.
Skurzef, I appreciate the information, but I won't be able to use it as of right now. Perhaps 1tonne or Relike would be more interested? I feel that the increasing joules are a great example of the effects of joule creep, perhaps you could test my findings based on the ratio you have in your set up (sorry not actually that familiar with the vsr-10 or any sniper rifle at the moment). Based on your set up I would guess your ratio is around 2.5. What's awesome about your information is that it shows that overvoluming past a certain point has detrimental effects on the energy of the bb, as KillerDad said.
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Old 04-25-2017, 06:02 PM   #13
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Except his ratio is 2.9:1

But when measuring these things, it should be with hopup off, and piston mass (and thus travel speed/time) also has a (potentially huge) influence.

Quote:
I have 'a' bb's. These would be best used with 'b' ratio. I can then alter my ratio of cylinder and barrel volume to best utilize these bb's.
Yup, this is basically how it's done nowadays.

Unfortunately, we really need to work on the knowledge we have on this subject as it doesn't always check out. A ratio of 2.9:1 is not always the best for a .43 bb. I know cases of guns with a 2.3:1 ratio performing best or very well with .4's (type 96's, for example). This is because of piston travel time. Thinner but longer cylinders can get away with longer barrels even if the cylinder has the same volume as a thicker but shorter cylinder. Or at least, that's my current hypothesis.

For VSR's though, at 500-ish fps, the current charts on this forum (or this formula) are accurate.

By the way, while we're at it, 303 mm with a VSR cylinder yields a ratio of 4.2:1 or so which means it's useless for just about all conventional bb's. The overvolume does potentially yield a lot of joule creep though.

I'm planning to do a complete study (yeah, the scientific way ) once I get some time on my hands.

Last edited by Reliku; 04-25-2017 at 06:05 PM.
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Old 04-25-2017, 09:09 PM   #14
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Quote:
Originally Posted by Reliku View Post
But when measuring these things, it should be with hopup off
A lot of clubs chrono the VSR10 with hopup on because they know that a VSR is opposite to an AEG. The more hopup, the higher the fps.
All of my charts are with hopup applied.
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Old 04-25-2017, 09:52 PM   #15
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Reliku, I would imagine that the reason for the longer cylinder advantage is based on the immediacy of the air being forced. I'll explain:

Let's assume we have two cylinders. Both with equal volume but one is half the length of the other (and as such as a greater diameter). Assuming same spring strength, one inch of movement on the shorter cylinder, actually moves more air, than the same inch on the longer cylinder. As such, the BB is being moved by this air. By the time the shorter cylinder finishes, the bb has been moved for x distance down the barrel. And the longer cylinder is still moving, thus pushing the bb further down the barrel.

I'm probably out to lunch with the hatter, but I think in there is part of the difference. And if i'm totally off my rocker, let me know and put me out of my misery.
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