What is the quality difference between...

[Sim123456]

a 35$ 650mm 6.03 Madbull inner barrel an a 220$ 650mm 6.01 PDI inner barrel. Except of course the .02 of diameter! Thanks!

[FOX_111]

Is it the heavy weight one?

I have a heavy weight tightbore for my L96. It doesn not flex at all and it's.... heavy. That might be the price difference.
It's also made of something other than copper. It's polished, silver in color. Might be steel.

[Sim123456]

Maybe, I tried one of the 650mm PDI in my L96 but never tought of tying a 35$ Madbull one

[Kos-Mos]

Madbull barrels are made out of aluminum and coated with some process similar to anodizing. They extrude the barrel then force a form inside it to even out the surface. That give a decent result for the cost, but the barrel will warp/twist depending on the temperature and other factors.
For the price, they are very good in an AEG, for about 3 years. After that, the finish get's ruff and you loose a lot of accuracy.

PDI barrels are made out of billet stainless steel, machined to exactly the right size and polished. They might contract/expand with temperature, but since it is a single, homogeneous piece of metal, it will always stay straight and even. There is no special coating to wear off too. If you checked the 10mm series, the outside diameter is 10mm instead of 8mm. That results in a wall twice as thick and a little over twice the material, meaning you would really have to try hard to bend/warp that barrel. The heavier material also helps a lot in absorbing the vibrations from the rifle's mechanism (the spring and piston ramming the cylinder, the gears/motor spinning in an AEG), resulting in a very increased consistency and accuracy.

If you want to get a PDI, you really should consider their 6.04 10mm series. They are a lot more accurate than 6.01 (though it seems stupid, field testing proved it). I think they are a bit cheaper too.

If you don't want to break the 50$ bar for a barrel, the Madbull ones are very good choices, way better than most china/unknown brands.

[Sim123456]

Ok, thanks a lot Kos-Mos for all the info! Very interesting! I know that PDI inner barrels also come in a metal tube so it can't be bent in shipping compare to the cheap plastic tube others usualy takes!