G&P gearbox m120 spring

[California]

Does anyone know how much fps a m120 gives off stock? How many coils do I need to cut to get around 390 fps?

[Jazzman]

Stock G&P m120 gearboxes shoot over 410. I don't know about cutting coils, but an m110 in a stock G&P should get you around what you want.

[California]

This is the G&P gearbox set I ordered. It comes with a 120. How can I lower the fps so it is conatantly shooting 380-390?

[ctres]

Just because it's called a 120 it doesn't mean you will be over 400. FPS can vary quite a lot due to poor QC in various parts of the gun, but particularly in the assembly of air seal components. Airseal largely depends on the nozzle to bucking and bucking to barrel seal as well, so if you had a bad leak in your barrel already you could be below 400 right whennyou drop in the new gearbox. Hence there is no guarantee for what your gun will shoot with the new gearbox.

If you are worried it will be too hot and want to be sure it is good to go before you show up to chrono then I'd say you have about three options.
1. Swap the spring
2. Cut off a few coils
3. Short stroke

[MayhemXXXFrosty (AndrewMp5k)]

Remember that springs will need to break in. So if it starts off shooting 410 brand new, it will probably settle around 400 or quite possibly more/less (springs tend to fluctuate after being worn in between ~5-15fps depending on brand).

[ctres]

Mayhem is right on, and he also just reminded me of another option. You can leave the spring compressed for a while and it will loose power, however that is just about the the most inconsistent way possible.

[Squirrel]

My G&P gearbox with a m120 was shooting close to 425. I dropped it to a m110 spring and its sitting around 400 now. My gun has a very good air seal though.

[California]

Just wanted to bring closer to this thread and let everyone who helped that my gun shot 390! Thanks again for the help everyone!