There are many misconceptions about airsoft gun barrels so hopefully this section will help to clarify what’s what.
Internal finish:
Firstly, the most important aspect of a barrel is the internal finish (we are going to assume that it is straight and not damaged). When a barrel is made the internal profile is reamed to size. Once reamed the inside of the barrel will need finishing as the reaming process will never give you a perfectly smooth finish. Barrel lapping is where the internal wall of the barrel is polish, ideally until it has a perfectly smooth mirror finish. Any imperfections inside the barrel will cause disruption to the bb and air as it passes through the barrel and will cause inconsistencies in the flight of the bb. If you look down a barrel, with a light source at the correct angle, you can sometimes see circles down the internal length. If these circles are very obvious and pronounced then the barrel has a poor internal finish. If the circles are very subtle then the barrel is good. If you can see no circles at all and the internal finish is bright and mirror like then the barrel is very good. EDGI for example lap their barrels by hand and so the internal finish to their barrels is some of the best available. Though with a little time and your own barrel lapping kit you can give most barrels a great internal finish.
So, a barrel with a poor internal finish will produce poor shot consistency. The better the internal finish the better the shot consistency.
Barrel length and bore:
The most common thing you will hear is that ‘you need a tight bore barrel for better accuracy’. This isn’t true. Simply dropping a tighter bore barrel into your gun will just increase the power of your gun. If your gun was underpowered then this maybe a simple and efficient way to increase its performance but that same performance can be got from simply installing a more powerful spring. If your gun is already at the power limits for your local site then it will be over powered once the tight bore barrel is fitted. A tight bore barrel and a standard bore barrel with the same internal finish and at the same power will perform no differently. So, we basically use bore size to adjust the power of the gun. Guns with shorter barrels usually struggle to produce high powers so tightening the bore of a short barrel will help to gain as much power as possible.
As a general rule, for most guns the tightest barrel bore you should use is 6.03mm. For guns with barrels shorter than 100mm a bore of 6.01mm is fine as the bb spends very little time moving through such a tight barrel and as stated above you’re always looking to gain as much power as possible from such short barrelled guns. For guns with very long barrels (500mm +) again 6.03mm is as tight as need to go but with very long barrels the manufacturing quality is key and you ultimately need to pay a premium for this. Though before investing is such a long barrel it is worth looking into if such a long barrel is really needed. With barrels longer than 500mm the bb is spending a long time travelling through the barrel which means there is more chance of the bb striking the barrel walls, striking more times, and ultimately producing a less consistent shot over a gun with a shorter barrel where the bb may exit more cleanly. So, it is a similar situation with barrel length. A longer barrel does not mean better accuracy. There are a few exceptions to this rule, but ultimately increasing barrel length will simply increase power.
Barrel material:
Barrels come is in three main materials: Brass, Aluminium and Stainless Steel. Usually, a better internal finish can be achieved with brass and Stainless steel so these are more preferable than aluminium. Brass and steel also react less to vibration as the gun shoots but if the barrel is correctly stabilised then this issue is negated. If you need a very long barrel (500mm +) then barrel straightness is key so the stronger material (stainless steel) would be preferable, but as we mentioned above a decent overly long barrel is usually expensive and not necessarily optimal for performance.
Barrel window:
A large, well finished barrel window is key. Small barrel windows will cut into and damaged hop rubbers when lots of hop is applied and small barrel windows will need to be machined bigger if you want to maximise performance from S/R-hopping. Most modern produced barrels will have large barrel windows.
You can also get barrels with bridged and un-abridged barrel windows. With a decent hop setup performance differences between these two types of barrels is negligible.
Barrel crown:
It is said that a deep crown is better though there is no hard evidence for this. This also goes for ported barrels. As long as the barrel end is cut straight and cleanly finished this is a good start.
Summary:
In summary, you won’t see big performance gains by simply changing the barrel in your airsoft gun. Here at Combat South we highly rate standard Tokyo Marui brass barrels and rarely swapped them out for an aftermarket item as it is a sizable cost for little to no performance gain. We will check the barrel of your gun before doing any modification and we will only replace it if it is poor, damaged or if the required power cannot be achieved with the standard barrel. Most standard barrels when combined with good power and a perfect hop setup will give great performance.