[cheapAEGboi]

This Data is for an AEG. 550mm is too long. If you do not understand, get around the 400mm mark as this is a pretty good all round length.

Thanks! I think I got it
after I play around with new cylinder I found that too much air or bad Barrel ratio will make 'sharper' pop sound(not sure if that effect accuracy or not),
kinda similar to real firearm with a short barrel when gunpowder burned outside a barrel and produce louder sound and bigger fireball

and if 'The longer the inner barrel the quieter' and 'too long barrel will make an airsoft inaccurate' maybe it possible to make a longer barrel without affecting an accuracy?

 

[1tonne]

Yip. All correct.
Short barrels do not effect accuracy by the way. Though they may produce less energy and can be over volumed.

 

[Zero Roaster]

One thing I have noticed with a shorter barrel...it is possible that it does not allow for maximum acceleration and stabilization of the BB when launched. Almost as if the shot is 'undercooked' so to speak. No matter what, overall, I'm still getting better results with a longer barrel.

 

[1tonne]

It depends on the bb weight. A heavier bb will stabilize quicker and so if you use a shorter barrel you need to change to a heavier bb.
Also, if the cylinder is ported correctly, you can get very close to the maximum acceleration. A full cylinder with the correct barrel ratio will always get more energy though but ported will be close.
Another advantage with shorter barrels is that they make it easier to put backspin on heavier bb's while longer barrels make it harder to put backspin onto a heavy bb. Short barrels have the advantage that if the cylinder is ported, the piston has time to accelerate and then when the piston goes into the compression zone, it is already at a very good speed and this creates a pressure spike that gets the heavy bb passed the nub. With Longer barrels that have a full cylinder, there is not much of the spike when the piston starts to move. So I have seen people say that when they use heavy bb's the bb will get stuck behind the nub. Shorter barrel have less likely hood of doing this.

 

[Zero Roaster]

Hmmm...interesting. I’ve never had a BB get stuck behind the nub. Mind you, I build some fairly monster hops. Nonetheless, yes and no on the fast piston. It works like an engine though...sure, it accelerates the air faster, but also less of it. No real gain there...just saying.


Sent from my iPhone using Tapatalk

 

[1tonne]

The bb getting stuck behind the nub happens more when you have a low fps build but want to shoot a heavy bb. So not so much with high fps DMR builds. It happens more in long assault rifles (around 350fps).

 

[Zero Roaster]

The bb getting stuck behind the nub happens more when you have a low fps build but want to shoot a heavy bb. So not so much with high fps DMR builds. It happens more in long assault rifles (around 350fps).

Oh! Ok...gotcha. In my world 350 fps is broken and gets scrapped. :lmao:

Alright, being slightly serious here, putting a heavy BB in a 350 fps gun is kinda moot, no? :shrug:

 

[1tonne]

No. Not always but I will go into that another time. There are good reasons.

 

[1tonne]

No. Not always but I will go into that another time. There are good reasons.

OK. So I can go into this just a little. (Our club now chronos using joules. They just changed in the last couple of weeks and I did not want to say too much about it since I wanted to keep my advantage. I don't have the advantage now and so I can say more)
The simple answer is, that it depends if you are allowed to joule creep.
An AEG chronoing on 0.2gm bb's and firing at 350fps (1.13j) can be made for fire ridiculously high energy rates. (I never JC'ed with a Full Auto as I think that 1.13 joules is plenty for CQB)
Here is a build I made (did not use in game) that fired 350fps (1.13 joules) but registered at 2.1 joules with 0.43gm bb's

117mm x 6.00mm inner barrel (Tighter barrels are better for JC)
Full Cylinder
Piston weight (I think it was about 60gm)
Spring: I think it was an M165 or M170
BB weight 0.43gm

 

[1tonne]

Oh. By the way, I have even created a 300% gain in energy while joule creeping a rifle but the inner barrel was that short that even with the heavy bb, the energy was not enough to make it worth using in game.


Here is another experiment that people may or may not want to do.
M165 Spring.
Normal Plastic Piston with no weight
40mm x 6.01 inner barrel
Produces 187fps on 0.2gm bb's (0.3joules. So not much)
Produced 208fps on 0.45gm bb's (0.9joules. So 3 times as much)


You could put in a bigger spring to make it more gameable but an M165 is already pretty big. You could also increase the difference in energy rates by adding weight to the piston

 

[ArcAngel]

Short answer,
18" barrel with .36g bbs and a m120 and no port cylinder and a full metal rack plastic piston and plastic piston head for a standard field legal rifle seems to be a perfect sweet spot for accuracy and power in my experience.

With that data I've lenghtened and shortened barrels for different fps setup and have had a lot of success with my recent builds.

The math at this point to me is meh to me. Its like one of those vertical line charts in my head, you move one variable up another goes down, then I move a third to compensate. Anyone else get what im saying? or am i nuts?

 

[1tonne]

Yip. Shorten the barrel and move the port forward stuff like that.
Or, put in a bigger spring and shorten the barrel.
One variable goes up and the other goes down.


You should check the energy rating of the 0.36gm bb with the 18" (450mm) barrel and then put in a 380mm barrel. It should make the smallest gain. Probably only about 0.05 joules though. So it is meh.

 

[FlatDarkEarth]

First off, huge thanks for this! Couple of questions on how this works - or let me think out loud:

-We're juggling a lot of variables here. Which factor is most important?

Energy
BB weight
Amount of Hop
Volume Ratio
Barrel Length

My gut says BB Weight, with Energy being close second, because the way the projectile behaves in the air is what we're really after. However, we tend to work with or think of guns in terms of energy output, so sometimes that becomes a primary consideration. Amount of Hop applied depends on BB weight, so there's just sort of a "right answer" for a given BB, but it gets colored by the other factors and type of hopup system, etc. Barrel Length and Voluming are just about efficient ways of achieving the above effects. And then those have follow-on effects in gearbox efficiency, sound levels, etc.

-So, if I start with the BB and work down the list from there: I want to shoot .32/.33g BBs. How little gun can I get away with?

-Now, let's impose a 1.5j limit as our primary consideration (because rules/playstyle goals). Is there a maximum useful BB weight for highly efficient bucking styles like a Crazy Jet/Hybrid, or a really well set-up RHop/flat hop in a 1.5j gun? Or, is there a practical FPS/energy floor for those styles of bucking?

-If so, what would be your highest expectation for the range potential of a 1.5J gun be?

 

[1tonne]

1.5 joules, I would use a 0.36gm bb and a 6.01mm barrel that is about 480mm will be somewhere around the most efficient ratio with a full cylinder. You could use a shorter barrel and also port the cylinder if need be.
There are minor variables that can change the ratios mentioned but overall if you have a 100% air seal, the barrel lengths should be about right. I guess the biggest variable is inner barrel diameter.

 

[FlatDarkEarth]

I'm surprised you recommend as high as a .36g. Seems like muzzle velocity might be a bit low, so I'm interested in why you find that weight works.

The first post mentions matching barrel length to ported cylinder volumes, but I assume we could do the opposite as well? In order to keep overall rifle length down and have a handier gun, I could give up some compression length? Then, maybe bump up a spring to keep it in the 1.5j ballpark, and hopefully since that energy level is all I'm trying to accomplish it won't be too extreme a gearbox setup - not too far into diminishing returns.

Edit: Oh, derp. Y'all just covered this a few posts before.

Edit 2: This tells me that the volume ratio is more important than the actual barrel length, in terms of the list of priorities in my post above.

My interest is more along the lines of maximizing an average size gun (m4 or similar) at average energies than in chasing the extremes of what's possible in a DMR. More of a sleeper build, I guess.

 

[1tonne]

I match all of my builds. My main M4 has a barrel length of about 190mm and with the port in the correct position, it works great. At 1.13j I use 0.28gm

 

[S/UMP]

Just worked out ratios using this thread.


Current spec AEG, max legal limit is 1.3j or 374fps @.20
Most game sites run a hard 350fps @.20 so no worrys about straying into a section 5 firearms offence.
So V3 gearbox, full cylinder 70x23.5mm, 247mm 6.03 barrel = a wopping 4.30 - 1
3/4 cylinder 46x23.5 = a nicer 2.83 - 1
1/2 cylinder 35x23.5 = 2.15 - 1



Haven't accounted for hop/nozzle volume or piston/head in cylinder. In short the very long awaited cylinder swap from full to 3/4 should make things quieter and reduce turbulance on BB's as they exit the barrel.

 

[tigerstr]

Ι must say that I found this article to be a great asset for my V2.5 DMR built. I would also like to add that a heavy piston head seems to play a big part in getting results ( best performance with heavy bbs). My built uses a 6.04 16 inch barrel and gives the best output (with a 130 spring), with 0.40 bbs. Exaclty as pre-determined here and planned in the built.

Many thanks to the OP ( @1tonne) and a... question for another of my builds, this time a "light DMR" configuration with a full V2 cylinder, type 0, a 16 inch barrel (407 mm) and a 120 spring, since I am pondering between a 6.01 Edgi and a 6.03 Promi barrel.

OP wrote:

NOTE: I have also noticed that when using a 6.01mm barrel, the barrel length can be increased by up to about 10% depending on the bb weight used. The lighter the bb, the longer you can go. This would be due to less air wastage.

Sounds quite reasonable but is a bit vague. What would be the "percentage length gain" for the barrel by using a 6.01 and 0.32 bbs and an 120 spring? Or maybe it would perform best with 0.36 bbs?

 

[1tonne]

For 0.32gm in a 6.01mm barrel = Anywhere between 400-440mm. It can be a little bit of a guessing game and so I would most likely go for 440mm.

 

[tigerstr]

For 0.32gm in a 6.01mm barrel = Anywhere between 400-440mm. It can be a little bit of a guessing game and so I would most likely go for 440mm.

Thanks for the prompt reply @1tonne , much appreciated! Will get back with the results of the upcoming built.