Quote:
Originally Posted by sgtscarfy
Is PDI really that bad? I hear good and bad things... why is the PDI so much harder on the mechbox when the Prometheus spring is stronger? If i was to be required to upgrade my mechbox and another spring, i prob shoulda just got a SystemA upgraded mechbox. Would have been easier and cheaper. Well im trying to remain CQB(<345ish fps) with this m4 so would a Prometheus M100SP be too much? I was looking on the spring guide from Illusion but not every gun is the same plus i dont want to go to a better mechbox. Im not made of money...
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A Prometheus 100 spring should be all you need. Don't rely on Illusion's spring chart too heavily, it is largely one study and uses a single type of gun with lots of upgraded parts. If you want simple, consider rules of thumb. Avoid all % springs. It's largely just PDI that does this, shipping out new employee's practice springs (a joke but I'm not fully sure that ISN'T the case). Other springs are rated in meters per second, so consider the numbers to be in groups of 30fps and it'll give you a ballpark fps number. So a 100 should put you around 330fps, a 110 to be around 360fps, a 120 to be around 390fps. Remember, ballpark only. Add in a bearing spring guide will increase your consistancy, but also add about 15fps, as well as make your piston hit the cylinder head a bit harder.
Regarding PDI springs, they are made from stiffer wire (and have no set length to them, I've measured 150% springs to range form 6 3/8" long to 7" long), but also they only have compressed coils at one end. Systema and Prometheus both have compressed coils at one end, but also the middle.
Here's a good example of two upgraded MP5s:
My SD has a PDI 150% spring in it, bearing spring guide, metal bushings, Hurricane reinforced mechbox and 330mm stock TM barrel. Last time I chronied it when it was healthy was last year and I sat around 387fps with 0.20g BBs. It uses an EG 700 motor and even with my 8.4V 3300mAh battery, it has a medium rate of fire, not very fast at all. Velocity went from 351fps with just the spring, to 365 with the bearing spring guide, to 387fps after adding a 10cm longer inner barrel.
My other MP5, which I've been using 80% of the year, has a Prometheus 110 spring in it, Guarder tappet plate, EG700 motor, stock mechbox, etc. Only velocity increasing part is the spring. It regularly chronies at 365fps and only has the stock 229mm innner barrel. It has a MUCH higher rate of fire than my SD, even when using a simple 8.4V 600mAh battery.
Nutshell, PDI springs suck. They comes in varying lengths, resulting in extremely inconsistant velocities. My reasonable PDI spring busted both the stock mechbox and a reinforced one. My stock mechbox with 110 spring only is still doing fine after lots of shooting this year.