The law states that anything with full-auto or burst fire capability has to be less than 1.3J, while single shot (includes semi auto, not just bolt action) has to be less than 2.5J. Most sites have agreed on 1.14J for AEGs and 2.3J for bolt action snipers, to keep them safely below the legal limits so that anyone turning up with a slightly hot gun isn't showing up with a section 5 firearm. DMR powers vary site-by-site based on what the site owner wants to include and deems safe to use.
So yes, you would need to either downgrade the power to 1.14J (350fps on a .2g BB), or you'd need to convert it to semi-auto only and be saddled with an MED as you'd be treated as a DMR at most sites if you're over that power level.
So yes, you would need to either downgrade the power to 1.14J (350fps on a .2g BB), or you'd need to convert it to semi-auto only and be saddled with an MED as you'd be treated as a DMR at most sites if you're over that power level.