Inner barrel length for a DMR?

[Cyclops]

My 1st gun (2 yrs ago) is a G&G 418 and I treat it like my kid. In other words I like to look at it instead of playing with it. Well my 2 yr warranty is up and I have decided to make it into a DMR. Should get more use out of it. Right now I have a 6.01 363 mm inner barrel with a mock silencer coving the inner barrel. Question is I'm modifying the gun to become a DMR. How long should the inner barrel be? I've been looking at 410 mm and I'm thinking that's going to be short. Should I get a longer one? Right now looking at the Action Army 6.01 410mm. Should I be looking at the 500mm? I'm also building a moch silencer to cover this barrel as well which is no problem. I just want to do it right the first time.
I'm also looking at the Prometheus M135 spring (430 - 500 FPS). I'm thinking the longer the barrel will decrease the FPS. My goal is 440 to 460 FPS. Keep in mind that I am getting the 6.01 barrel as well.

[McNair]

A M16A2 inner barrel length is 550mm. Start there.

[Nodachi]

Barrel length really doesn't do much of anything for accuracy and range, to be honest. 509 is the standard M16/M14 length barrel length but any more than that you'll have to start increasing the volume you're pushing out of it by doing bore up, which isn't that great of a ROI. You can get some pretty good results with a good quality 363mm like PDI or Prometheus (PDI 01 is probably the best for the money) and then tweak the compression and hop to get it running perfectly.

[Cyclops]

Looked up PDI and wow cost is nuts. $160 and claims to be on sale. Why is it so expensive? Never really looked into it.

[Nodachi]

Buy them direct from PDI, their distributor is at http://www.x-fire.org/etop/01.html

They're expensive because they're precision machined stainless steel, with no teflon coatings or any of that business that is often used to make up for looser tolerances. The tolerances on a PDI barrel are ridiculous and they will last just about forever.

They do have a budget line, the Raven 01+ that's just got slightly lower tolerances, made from carbon steel, and a light teflon coating, but still performs very well.

http://www.x-fire.org/etop/01+.html


Here's a comparison of common Japanese-made AEG barrels.

Outside of Japan, Core and ZCI are pretty decent, I would put them somewhere below Prometheus and above Madbull.

http://imgur.com/a/W2DSn

[ballarms]

for my dmr i use an m16a4 just cause i like it more then the a2 or a3 but its all up to you