Upgrading an HL airsoft gun is as much an art as it is a science. I've been involved in this hobby for over 2 years and have been tinkering with the HL guns for as long. Through trial and error (and I have about 50 destroyed airosft units to prove it) I've pretty much figured out how to maximize the power of the HL tank's main gun through a combination of upgrades to the airsoft unit and replacement of the inner barrel. It's hard to describe all the steps involved but its about a dozen things you need to do to get the unit to work to it's maximum potential (and there's still a risk of the gun self destructing when using it. All my tanks shoot well over 100 feet (and well over 200fps) I just finished modifying my Panzer IV (pics included in another thread) which includes a modified airsoft gun and lathed madbull 6.03mm inner diameter barrel that shoots over 150 feet. I always maintain these are not toys and can really do some damage if hit by a bb (so always wear safety glasses)