I am looking for something to start off at when fiddling with my phantom for efficiency.

What spring combination do you use? What other mods did you do? how many shots to the 12G do you get?

I just bought my phantom, and my tinkering nature will not allow me to leave it untouched... :D

What do you call efficient ?
Number of shots per 12g?
Consistent velocity?
Accuracy?
Range?

I can get more shots off a 12g with a softer valve spring and mainspring, but velocity fluctuates.
I can get more consistancy with a stiffer mainspring but a medium valve spring, but my range will sometimes be less.
The scientific method
Buy a set of Nelson springs, start with the stiffest valve spring and softest mainspring-go through a dozen 12g's and record range, accuracy and # of shots before it drops below your pre-determined velocity. Do it over a chrono and be prepared to spend several hours and a case of paint recording your results.
Then change the mainspring and do another dozen 12g's. Once you've gone throught the four different mainsprings in the kit, change the valve spring to the next(softer) spring and start over with the mainsprings.
Keep in mind you're recording averages, each 12g will be slightly different. That's why you need to record a number of them each time you change springs - you can't take an average from one single (12g) try.
Do all this with your hammer velocity adjuster in the same place each time. Wrap the threads in teflon tape to keep it from moving and set it to about the middle of it's range before you start.
Once you go through all that, you should know which combination of springs will give you the type of efficiency you want.

My accuracy with different barrels can change with the velocity, My stock 11" barrel is more accurate at 265fps at medium range than at 290fps at the same distance. The 8" barrel runs 10fps faster than the 11" on average, all else being equal.
The new CCI 18" barrel is a fast favorite for me, the paint doesn't roll out!

I can't guarantee you will have the same results but after trying almost every combination and shooting hundreds of balls I settled on the green (medium) valve spring and the yellow (light) mainspring. I also removed the pump return spring.

Before I got 25 shots average per 12 gram and had a pretty tough pump stroke.

Now I get 40 shots per 12 gram and my pump stroke is butter smooth. I can pump it easily with two fingers and because it is so light my aim stays much tighter when firing mass balls.

The only negative is I have to make sure to push the pump all the way forward or it won't shoot but this does not happen often. I was shooting at 280 fps and it was 85 degrees, low humidity and I was shooting marbs with a red detente ring.

I hope this saves you some time and paintballs. Good luck!

i was thinking about doing yellow and green, i think i will.

right now, i get 40-ish to the 12g, but i am using the stock mainspring and a very heavy valvespring (the pump stroke sucks).

however, i might go with a red valve spring and a green mainspring, provided i can get the velocity up. if not, i will go with the next higher mainspring. that should keep it consistant.

anybody modify the internals any?
I am thinking about grinding the adjuster down to get a little more flow around it, see if that helps any. it cant really hurt, anyway...