2 hours out of an 11.1v battery is awesome… I get about 3-4 magazines out of mine and the low voltage buzzer goes off… are you using an 11.1v LiPo or LiOn battery? (round/cylindrical or square?)
The motor is enclosed in the airtight grip with your hand around it keeping the heat in… so it has NO cooling at all… so it will get very hot. It will get hotter faster doing short bursts than it would running longer (it takes more battery to start and restart the cycle than to start it and keep it running)… but if the motor is run for long periods, the motor can eventually melt the hand grip (or burn itself out).
So, there is nothing wrong with your blaster, that is just how they are. When you feel it getting uncomfortably hot… you have to give it a break… that is why most of us have more blasters than one
I cant understand why motor cooling has not been included in blasters… all RC planes, helicopters, buggies and boats… they all have airflow cooling the motors… our blasters are all completely airtight, for want of a better word.
The barrel size (id) depends on what gels you use. I have different barrels for different gels… you cant squeeze a 7.3mm gel down a 7.1mm barrel nor get any fps out of a 7mm gel in a 7.5 mm barrel
The best result in fps you can achieve in our blasters is to have the correct size gels for the barrel… so you need to measure the gels you are using and fit the correct barrel for that size gel…
1.3mm is a good thickness spring… especially when the O ring has been done and you have no leaks around the T piece and a good alloy or brass barrel