Trying to get my head around barrels

[Amoki]

I need some explanations on 2 things related to barrel:

1) since the barrel in an AEG serves as a directional chamber that builds up pressure and end up pushing the BBs out of the barrel and since the BBs don't get in contact with the barrel, then in theory Your higher end TBB barrel e.g. Madbull 6.03mm and Prometheus 6.03mm should give similar results to a Vanaras 6.03mm or a ACM 6.03mm barrel (think CYMA SOC16s).

Yet anecdotal evidence from the Net doesn't seem to support this. And if I remember a review correctly, there was a case where a EDGI 6.01mm TBB has poorer groupings performance than a Prommy 6.03mm barrel of the same length on the same platform with the same hop-up rubber. Infected Airsoft has a documented a similar result when the Vanaras 6.03mm TBB he used gave poorer groupings result than a 6.08mm Marui barrel of the same length on the same TM MP5.

Why? What causes grouping variation between barrels? I would presume they are all made from the same process but receive different post-process treatments. But then since the BBs are not in contact with the barrels, post-process treatment should not make a difference, and therefore an investment in a good hop-up rubber and nub THAT MATCHES THE OUTER DIAMETER OF YOUR TBB to increase consistency in the friction interface as well as FPS output will result in a far more dramatic improvement in accuracy then buying an expensive TBB?


2) Does longer barrel affect accuracy?

I've been doing some re-reading back on my engineering thermodynamic textbook, and on pipe length design, the Hydrodynamic Entry Length - the length where airflow is reach stablity, is approximate ~10X diameter, which seems to suggest that the longer your barrel is, the more stable the flow of air/pressure behind your BB will be, and the more accurate your BB will end up. And when coupled with proper cylinder matching, you get to ensure you put just the right amount of pressuried air.

But then pipe thermodynamics isn't exactly applicable to airsoft since we are dealing with a projectile that continually builds up pressure and speed while inside the chamber, and if the barrel is only there to "direct" where your BB should do AND serves are a platform for pressure build-up, then in theory a 300mmm barrel should be as accurate as a 400mm barrel though with less range and FPS to boot. But if this is true, then proper cylinder matching will not affect accuracy at all. And therefore an airsoft M4 (363mm) has the capacity to be as accurate as a airsoft Steyr, M14, and M16(500mm).

Thoughts?

[yuhaoyang]

Despite manufacturer claims of inner barrel diameters and ect. the lower quality ones will come with imperfections, or their inner diameter could be off in extreme cases. Hence a barrel made using a more precise and higher quality machine with higher quality materials will end up being better, and more expensive. (this excludes madbull, which uses a special coating thing).

someone will probably come along and correct me on that in a sec.

[Skruface]

Originally Posted by Amoki

I need some explanations on 2 things related to barrel:

1) since the barrel in an AEG serves as a directional chamber that builds up pressure and end up pushing the BBs out of the barrel and since the BBs don't get in contact with the barrel, then in theory Your higher end TBB barrel e.g. Madbull 6.03mm and Prometheus 6.03mm should give similar results to a Vanaras 6.03mm or a ACM 6.03mm barrel (think CYMA SOC16s).

Depends on the interior finish of the barrel as well. High end barrel might have a runout of 6.03mm +/- 0.005mm; a cheaper barel might be 6.03mm +/- 0.75mm.

Originally Posted by Amoki

2) Does longer barrel affect accuracy?

A longer barrel gives the BB more time to stabilize; there has been some evidence that beyond a certain length, this becomes negligible . It doesn't really affect range if your cylinder is matched properly; what it does (from years of experience; I have no measured empirical evidence to back this up) is make the spread of your groupings smaller at longer ranges. The grouping from my Systema 6.04 AK47 inner barrel (455mm in length) was something like 8 inches at 40 yards. I swapped it out for a SIG550-length inner barrel (Systema, 6.04ID, 534mm long) and the grouping got smaller by about an inch and a half using the exact same setup, hopup rubber, and ammo.

Note that hopup rubbers are just important as barrel length/diameter, if not moreso. You have to have just the right "grip" to get the best backspin to keep the flattest trajectory possible. That said, I like Prometheus "Hard" and Firefly "Spicy/Kurage" hopup rubbers for my guns that shoot over 400fps, and Guarder clear "enhanced" rubbers for the ones in the 280-380 range. I also use Big-Out "H"-nubs for my hopup buckings, as they give 2 points of contact on the BB as opposed to 1 with a standard hopup bucking.

[Azathoth]

Their is a huge discussion on this in the filairsoft forums.

To summarize:

The maker of the EDGI Barrels speculates that it is the Quality of the BB's and ratio between the Diameter of the BB and the inner barrel Diameter that affects groupings.

He measured BB Diameter and found that it varied from 5.89 (excel/KSC) to 5.97 (Goldenball). He found that goldenball BB's fired through stock TM barrels produced groupings comparable to KSC/Excels fired through a 6.03 tightbore. The findings are supporting his theory that their is an ideal bb diameter to inner barrel diameter in the range of 0.11-0.14mm

Originally Posted by Skruface

I also use Big-Out "H"-nubs for my hopup buckings, as they give 2 points of contact on the BB as opposed to 1 with a standard hopup bucking.

I use the SCS, I noticed a huge groupings improvement over standard nubs and "H" nub that is in line with what is seen in filairsoft. The other noticable difference is the amount of hopup you can put onto the BB.