[Kos-Mos]

I am typing this on my phone, since I have time to waste waiting for a bus.

Fisrt thing, all batteries are rated by their nominal voltage. For a LiPo, that is 3.7v/ cell. Times 3 cells is 11.1v. But all battery types actually have a higher actual voltage. In fact, when the voltage no-load of a pack is it's nominal, it's empty or just dead (if it's fresh off the charger). That means that a3 cells LiPo is actually up to 16.6v when full charge, as each cell can peak at 4.2v.

If you have to wire batteries in Series, you want to make sure that both are exactly the same brand and model, where made in the same batch and have the same wear/nuber of cycles. Otherwise the pack will fail, and in the case of LiPo, probably explode.

I am not sure what FET is in the MERF, but 99% of high power FETs are rated for 40v DS. It's more likely that the CMOS microcontroller fails, as it is made to operate between 10 and 15v. And there is probably not an on-board regulator for such a simple device. In theory, a homemade "simple" FET can take 40v/100A easily (yes, that's 400W).

The problem comes from the motor. The ones in our Rifles are designed for 5-7v, and we run them at 10-12v most of the time. You would have to increase the number of coils on the rotor and probably need to reduce the size of wire used to fit it. That would result in a more efficient system (less heat waste due to current), but equivalent RPM.

So all in, running a 22.2v/6 cells LiPo on a gun designed for 14v will simply result in a burnt motor, FET and potentially gearset/piston.
Keep in mind that once the insulation on the motor rotor wires is melted, that will short out your battery until the FET blows, so you also add a pipebomb in the mix, LiPos in metal tube are nasty.