Air guns with muzzle energy over 10 J must be registered (gun license is needed).
Power (muzzle energy) will, of course, decrease accordingly.
Available factory loads can produce nearly 1,800 ft lbf (2440 J) of muzzle energy.
From the beginning, combining high muzzle energy with projectile density and hardness have been the foremost factors in the design of such weapons.
Airsoft guns that exceed either of the maximum velocity or muzzle energy are considered firearms.
In Japan, airsoft guns are legal, but may not shoot with a muzzle energy above 1.00 joules.
I'd guess the muzzle energy at about a ton and a half.
A limited number of 'hunting' loads are available commercially, which produce about 25% more muzzle energy than the more common target ammunition.
Resources were therefore spent on research into other programs that could provide the needed muzzle energy.
The bulky silencer would shave a bit of muzzle energy, but that was fine.