You can't use an APS cut inner barrel with a PDI chamber. The PDI chamber uses an AEG cut inner barrel, while the stock chamber uses an APS cut inner barrel.
I've posted about my recommendations in the other thread. I like 6.01's, which are the only barrels available that are perfectly sized.
However, if you'd like to steer towards the 6.03 route, then that is fine too. It's all pretty theoretical as to which one is better, and I like to be open minded until there is a definitive answer. Just know that, with a 6.03, you'll have to get either a barrel that is shorter or longer than your outer barrel.
Again, if you want to get a shorter inner barrel (which would probably be easier), then you'll have to widen the muzzle slightly. It's pretty easy. Disassemble your gun and take separate the outer barrel by itself. Take a drill and use a drill bit that is bigger than the muzzle's hole, and 1 minute later, you're done.
Your best options for length would probably be 469 mm (G3/SG-1), 455 (AK), and 407 (M4 Plus). The shorter the barrel, the wider you should make the hole.
Personally, if I wanted to go with a shorter, larger diameter inner barrel, I'd get this one:
http://shop.ehobbyasia.com/km-6-04mm-tn-inner-barrel-for-g3-sg1-469mm.html
KM is also a fantastic inner barrel maker. I'd either go with the above one, or a Madbull, since Madbull's is aluminum and can break in.
As for if you want to get a longer barrel, I don't know how you're going to get that orange tip off, but once you do, we can talk more about longer barrels.
I've posted about my recommendations in the other thread. I like 6.01's, which are the only barrels available that are perfectly sized.
However, if you'd like to steer towards the 6.03 route, then that is fine too. It's all pretty theoretical as to which one is better, and I like to be open minded until there is a definitive answer. Just know that, with a 6.03, you'll have to get either a barrel that is shorter or longer than your outer barrel.
Again, if you want to get a shorter inner barrel (which would probably be easier), then you'll have to widen the muzzle slightly. It's pretty easy. Disassemble your gun and take separate the outer barrel by itself. Take a drill and use a drill bit that is bigger than the muzzle's hole, and 1 minute later, you're done.
Your best options for length would probably be 469 mm (G3/SG-1), 455 (AK), and 407 (M4 Plus). The shorter the barrel, the wider you should make the hole.
Personally, if I wanted to go with a shorter, larger diameter inner barrel, I'd get this one:
http://shop.ehobbyasia.com/km-6-04mm-tn-inner-barrel-for-g3-sg1-469mm.html
KM is also a fantastic inner barrel maker. I'd either go with the above one, or a Madbull, since Madbull's is aluminum and can break in.
As for if you want to get a longer barrel, I don't know how you're going to get that orange tip off, but once you do, we can talk more about longer barrels.