Hey Guys,

After being a little dissapointed with the accuracy and range of my stock JG M4 S-System 2010, I decided to spend a crazy ammount of money and purchase a 455mm long, 6.01mm ID (internal diameter) stainless steel tightbore barrel by PDI (~$125). Now, the stock barrel for an M4 is typically 363mm, so I capped the end of it with a sweet looking suppressor (SRC KT Silencer - ~$40) to act as a barrel extension.

The barrel cost almost as much as the gun, but after doing some testing of before and after the upgrade, it was completely worth it. My grouping accuracy doubled (ie while shooting at the same point on a target, the hits landed closer to previous and future shots).

Before I did this now, I read a TON of articles about this. You are going to hear a lot of crap out there from idiots who know nothing of physics. Here is some of the CRAP you may hear:

• A longer barrel does not improve range
  
  This is both true and false. Longer does not neccesarily mean greater range, but it doesn't hurt when you have a tightbore barrel. Why? It is real simple: the less of a gap between the bb and the inner wall of the barrel, the less air that escapes from behind the bb, meaning that "puff" of air stays behind the bb for a longer duration without diffusing around. The perfect barrel would be of a diameter closest to that of the diameter of the bb but not so close that the bb scrapes the metal walls versus being padded by a softer (lower coefficient of friction) wall of air surrounding the bb, and it would be of a length where the bb has used all potential energy provided by the inital "puff" of air (ie it travels along the barrel until the pressure of air behind the bb is no longer providing an accelerating force, and the useful energy of that "puff" is exhausted, usually from diffusive forces through the gap between the bb and metal surface).
  
  The best way to compare this is via cross-section areas. A 6mm bb leaves only 0.33% of the cross-section of the 6.01mm ID barrel unoccupied. A 6.03mm leaves 0.99%, and a 6.08mm (what many stock barrels are) leaves a whopping 2.61% of the cross-section empty for the "puff" to escape.
  
  I basically replaced my M4 barrel with an AK-47 barrel... not exactly a huge jump, but you don't want to lengthen the barrel too much if your weapon does not have a motor set that can use that length to its advantage. All you will be doing is carrying around a big, exspensive gun that doesn't do much for you.

• Any smaller than 6.03mm is overpriced and not worth it
  
  Yes, I probably paid too much for a stainless steel tube that is "slightly" better than a 6.03mm, no argument there, but you can get them cheaper. As for 6.03mm being this versitle, well-rounded internal diameter... makes no sense. You may get more bang for your buck with a 6.03mm (I compare it to buying slightly older video card for your computer versus buying the latest and greatest), but if you want that slight edge, you have to pay for it.
  
  One of the ridiculous arguments you will hear about is whether the bb is completely cushioned by air as it travels down a barrel, or whether it is riding/sliding along constantly in contact with the metal surface, and that somehow a 6.03mm is better in both ballistic scenarios. These arguments make no sense. Let us assume the worst-case scenario, that the bb is sliding along the wall. If you are packing 6mm bbs that are flush against the barrel inner surface, that means you have 0.03mm (give or take) of open space where the air from the "puff" can escape from "pushing"... lost energy. Now, even if the bbs "ride the rails," how could a 6.01mm barrel in that same scenario be worse than a 6.03mm? Think about it... As for the scenario if the bb is completely surrounded by a cushion of air, it is still the same resuly... you need that air behind the bb, not diffusing around it.
  
  Personally, I think people like the idea of 6.03mm because I think they use crap ammunition, and you cannot use crap ammo with a 6.01mm... don't even bother. Also, you need to clean your gun like a fiend compared to most who probably have no idea what cleaning is all about, or how to even do it. Also I hear some stuff about turbo guns not handling 6.01mm well. My guess is because they have crappy internals that do not work well with the barrel, or since they burn through bbs, they use crap. In summary, do not buy a 6.01mm barrel if you do not maintain your gear.

• It's just like gun ballistics
  
  No, it is not! Theres no gunpowder exploding and constantly expanding at an extremely rapid rate. Your airsoft gun is not a controlled explosion (though some may claim). A 5.56 × 45 mm rifle has an average muzzle energy of 1,796 joules. For a 0.25g bb being shot from my M4 @ 380 fps, using Ek = (1/2)mv^2 (remember class, a joule = a Newton meter, so unit conversions are required), that translates to 1.7 joules... one-one thousandth of a real M4s chemical energy. Real guns do not have "hop-ups" either.

CONCLUSION:

No one has been able to convince me as to why anything but a 6.01mm is better than everything else. Going from a stock barrel (which was probably around 6.06mm or so) to a 6.01mm is a big step, but if you already have a 6.03mm, then going to a 6.01mm probably isn't going to do that much for you and be worth the money. So, if you are going to upgrade, I see no reason NOT to go from a stock to a 6.01mm, unless you are that cheap with the bbs or that careless with your gun.

EDIT: As Grinder reminded me, 6mm bb's are actually closer to 5.95mm, however, this does not change the conclusions. It changes the exact values, but the proportionality remains.

Im looking to get my barrel replaced with a tight bore as well but I am new to airsoft and I dont know what barrel length I should get or the diameter. I have an M16. I heard they have a longer barrel length then an M4 but I don't know the length or the diameter of the stock barrel. How can you tell?

If you know the exact model of your gun you could look it up at one of the on-line stores like: www.ShortyUSA.com

If you find your gun they will tell you the barrel length and other specifications. If I'm not mistaken, all standard barrels have a 6.08 mm ID (inside diameter), so your tight bore choices are 6.03 and 6.01.

I have used 6.03 and even 6,04 and the increased FPS and accuracy has proven worth the investment. Every time you replace a barrel, shot the extra bucks towards a new Bucking/Nub. it will be worth it.

Okay thank you everyone for your input! My gun is a 1:1 scaled replica of an M16 so it should have the standard M16 barrel length. Another question: What is a bucking/nub?

Buckings are a short thin rubber (can be other material) tube that slides onto the hop up end of your inner barrel. This will slide into your hop and give you an air seal between your barrel and hop. A good bucking is worth its weight in gold if you can forgive the expression.
Personally I like the Madbull fishbone reds but many techs will have many opinions.

Nubs are a small tube or concave or convex bit that sits between the swing arm of the hop and the bucking. Generally made from rubber, plastic, poly, or a few other materials. It fits into the cutout of the barrel and applies pressure to the BB and creates backspin as the BB passes threw the hop during discharge. SCS are a popular concave nub and some guys even make their own but this is for more expierenced techs and I wouldn't try it until your more comfortable with working on your weapons.
Here is a graphic to help


The hop-up rubber would be what is called a Bucking

wow you really know your stuff, thanks for the information. i wanna get my barrel replaced with a v2 madbull black python 6.03 soon. Should i get a new bucking or nub because the stock ones will not work with it?

You don't have to get new but I would recommend the madbull Fishbone reds if you don't mind an extra $10.
Here is a link to show you what I mean but not saying to buy from ASGI (I don't at least).
Madbull red

The alum aren't bad at all. I have a Madbull 7075 6.01 in my M14. Alot of inners are brass also. I don't have any that are steel tho. Just make sure you choose a good high quality inner.
A few things you will always want to upgrade in an AEG are the inner barrel, hop-up, and bucking/nub.

Higher end hop-ups are better made with more precise tolerances and better materials. Metal hop-ups are the way to go if you ask me. Prometheus are argued to be top of the line. I agree. Hops are the begining of the BBs life in the firing process and are the first main part were air leaks can begin to happen. Air leaks are the enemy.

As for the barrel, I would say the Madbull but I am a fan of Madbull inners and a little bias. Really it is all just personal opinion. Techs all have diff ideas in what they say are the best. Try one out and see if it works for you. All guns are different and get results that vary.

With a little observation, I found out that my gun comes with a stock metal hop up. I guess lower-end AEGs come with plastic ones, so that saves me some money. I think I am set with upgrades, gnna order them and have the army navy shop install everything. I dont want to take the chance of doing the work myself.. Thanks Vanish for all the info.