Cutting 3/4" to 1.0" off of a flash hider renders it pretty useless and if you end up with open tines that will cut your carrying case or tear up your car's upholstery.
I faced the same problem on one of my AR pistols so just bought a cheap nice looking short threaded barrel cap from E-Bay (looks better than a hacked up A2). Tons to choose from on E-Bay.
I know everybody says that a threaded-on flash hider doesn't count towards length, you might very well win that one in court but can you win that argument on the side of the road with a pissed off LEO that doesn't approve of a civilian carrying a short AR. Personally I chose to just shorten the gun so no argument , no convincing, no threatening needed. I don't have the time or the money to go to court to get my gun back.