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One of the most common questions surrounding barrels is "which bore diameter is best?"
General consensus on the interwebs is that the smaller the bore
diameter, the better your accuracy will be. Typical 'small bore' sizes
usually start at 6.03mm and go down to 6.01mm to 6.00mm. There are even
ultra rare sizes such as 5.99mm diameter barrels too.
Larger bore sizes tend to start at 6.05mm to 6.08mm and beyond.
One of the first things you need to realize with any barrel is that its
performance is largely at the mercy of the BB's you feed it. Lets take,
for example, one well-known high quality BB on the market today: the
6mm Bioval. Bioval advertises their BB's as having an average diameter
of 5.92mm, which is billeted as being smaller than most manufacturers.
Most well known brand name quality airsoft BB's tend to have an average
diameter of 5.98mm +/-. That +/-
figure represents the margin of manufacturing deviancy possible. If you
were to take a pair of dial calipers to your BB's and measure each and
every one, you will find that they are not uniformly 5.92mm as in the
case of Bioval's, or 5.98mm or whatever else they are advertised as.
Generally the more expensive the BB, the more uniform the diameter
consistency versus a cheaper BB brand will be. Cheap BB's can have some
pretty wild diameter fluctuations to the tune ungodly numbers that
shouldn't even be fired down the cheapest hand-forged-barrels-from-scrap
oil-drums-sourced-in-the-landfills-of-Papau-New-Guinea.
Bringing the discussion back to barrels - slinging your 5.98mm +/- BB's
through a 6.00mm diameter barrel doesn't leave a very big margin of
error. If your BB diameter is too large, it will cause jams and accuracy
issues as it is being forced down too tight a bore and/or 'shaving'
itself along the way. On ultra-tight bores, if it is shaving the BB's,
it will eventually decrease the diameter even further as the BB's leave
their residue behind. BB residue is also bad for accuracy too. The
smaller the bore you go, the narrower the range of BB brands you will be
able to choose becomes - ironically, this also means the cost of
feeding your AEG becomes exponentially greater, as ultra-high precision
BB's are more expensive than their less precise counterparts.
For small bore diameter barrels, I feel 6.01mm is the absolute smallest
one should go, while 6.03mm is a good compromise to account for those
who use a wide variety of BB brands.
One school of thought
suggests that a larger bore diameter is actually MORE conducive to
accuracy than a tighter bore. There are a fair number of well known tech
guru's who have conducted the testing and even used specially
manufactured clear acrylic barrels with high speed photography to
capture the BB's 'flight pattern' so to speak and determine just how
exactly the BB's act when traveling down a barrel. Testing seems to
suggest that when exiting the hop up chamber the BB travels along the
top of the bore and generates its spin along the way (in somewhat
similar fashion to the Tippmann flatline barrel in paintball.) Thus, the
less friction and obstruction imparted on the BB by the barrel the
better it will be for accuracy. Additionally, it was determined that
there were negligible gains on longer barrels over 450mm's in length. My
own testing has seemed to confirm that larger bore diameters (6.05mm)
tended to to result in better accuracy (the caveat being that your
gearbox and hop up unit are operating in perfectly tuned harmony too.) I
have several setups where I transitioned from a 6.01mm to a 6.05mm bore
and noted demonstrable accuracy gains and range improvements.
So there you have two polar opposites in barrel thinking. Which one is
correct? Well, you have to realize again that there is truly no precise
clear cut answer for which barrel diameter is best for you. A
combination of factors effect barrel accuracy, including your hop up,
gear box performance, BB's and overall bore cleanliness.
Discuss - what has been your experience with barrel bore diameters?
Next topic will be discussing the particulars of barrel brands, what's hot, and what's not
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