[Zoms101]

TL;DR: Your opinions on this article's statements about barrel length.

Hello there, Airsoft Society! I recently (mostly) built my own AEG based on the AR platform. This was my first time building an airsoft gun from the receiver up, and I hit many snags along the way. I also learned a lot too.

But one thing I'm still not entirely sure about are the factors governing range and accuracy, most notably barrel length. The gun I built has a 20" 6.03mm barrel (yes, it is as unwieldly as it sounds). I originally did this with the notion in my head that a longer barrel equals more time for the BB to be accelerated by the air in the piston cylinder, and therefore have a longer range. I also assumed that a tighter bore barrel would be more accurate. I picked a 20" barrel because it was the correct length for a full piston cylinder (i.e., no cutouts) that would use its full volume of air.

Upon receiving my gun back from Evike custom services (because I can't shim a gearbox to save my life), I hefted it and realized my mistake. I now want to make a shorter gun, but without sacrificing long-range accuracy. To this end, I am now doing a good amount of research and have come across a few articles that say that accuracy, range, and barrel length do not all increase linearly. To summarize: I know barrel length gets you better results up until a certain point, after which there are diminishing returns; also, there are other factors more important to range and accuracy (i.e., hopup and BB quality).

Most recently, I have read this article, and would like your opinions on its statements, specifically its statements on barrel length. What/how much effect does barrel length have on range? Is that article's claims accurate with your own experiences?

Thanks for reading my ramblings, any response is appreciated.

 

[Zoms101]

I thought I'd add this in the replies so I could keep the main post short:

If there's enough interest in this, I might start collecting data from users on barrel length and other factors and create some performance graphs to better realize their relationships.

 

[Ben3721]

The barrel determines only like 20-30 percent of the accuracy. The rest is from bb, hop and fps consistency.

For airsoft a bb rides on the top of a barrel from the backspin all the way out of the barrel. However the bb skips a few inches after being hopped. Lighter pressure hop applications like flat hop, r hop or a softer packing helps reduce this skipping effect. Longer barrels with a wider bore or a more polished bore stabilize the bb before it leaves the barrel with minimal side influence on its spin. If it hits the sidewalls hard while skipping or riding the top of the barrel the bb may curve some. This isn't some BS I'm pulling out I'd theory, I have seen barrels cut lengthwise and seen the bb residue patterns to know this. It is a thing.

Barrel length for fps differences can be compensated for with ported cylinders. But there is a pressure difference between short and long setups, from my experience low pressure long setups seem to be slightly more consistent. Probably less skipping and more length to calm it down.


Personally my own setups I use lapped Prometheus 6.03 barrels with Elvish tac r hop patchs with 3D printed pivoting R hop arms I designed myself for the most even centered pressure possible that I've ever achieved.
I also have my nozzle seating deep into the packing while seating the bb back right at the start of the patch by custom cutting the tip. I use BLS .28, and I have cut some in half to ensure they have zero air pockets. I also make sure my hopups are as level as possible, and shim my hopup rotation if needed.
The more details you put into it, the more accuracy you'll get.

 

[Guges Mk3]

You originally went into your project thinking your AEG is a "Firearm" - Expanding Gases

Rather it is a blow gun - Compressed Air of a certain Volume and related pressure wave.

Pick you barrel length and then set your FPS limit. At that point, then work on accuracy factors.

 

[Zoms101]

...
For airsoft a bb rides on the top of a barrel from the backspin all the way out of the barrel. However the bb skips a few inches after being hopped. ... Longer barrels with a wider bore or a more polished bore stabilize the bb before it leaves the barrel with minimal side influence on its spin.
...

That seems to be the consensus of the article. It said that within 260-500mm length, the performance difference from barrels is negligible unless running a long-range build.

...
Barrel length for fps differences can be compensated for with ported cylinders.
...

I remember reading that having too much or too little air pushed through a barrel from an improperly ported cylinder can negatively impact accuracy, and that there are specific amounts of porting needed for different barrel lengths. Is this true?

 

[Guges Mk3]

Nope. Over or Under Volume is an efficiency issue, not an accuracy issue. It mainly affect FPS of your bb.

Long range builds do not require long barrels. I have a 178mm barrel on my G35 Replica, Using a Maple Leaf MR 50 and .23-.28g bbs. I out range stock AEG's and have better accuracy.

 

[Ben3721]

That seems to be the consensus of the article. It said that within 260-500mm length, the performance difference from barrels is negligible unless running a long-range build.

I remember reading that having too much or too little air pushed through a barrel from an improperly ported cylinder can negatively impact accuracy, and that there are specific amounts of porting needed for different barrel lengths. Is this true?

"Theoretically" if somehow the bb starts decelerating inside the barrel from under volume it technically has less of a air cushion. But you'd have to do something stupid like half the needed air volume for a 400mm barrel.

Over volumed setups are common for heavy bbs, but the negative effect on the bb would be if the outer barrel/attachenent is longer AND not centered at all to the inner barrel it could push it a hair one way, probably more on like long fake suppressors that have let's say a 8 to 10mm ID, if it was off 2mm it could create accuracy issues. But not by much.

I agree with guges, get a length that you want for your play style then go from there. Just don't go under 200mm and you'll have a pretty good starting point.

Might have said this before tho, high pressure short barrels are much louder than long barrels even if volumed appropriately for the length.