Today I purchased a new Colt 6920 carbine. I added a midwest Industries aluminum Quad rail and plan on installing a ambidextrous sling mount. MY question is how do a loosen the castle nut? I bought a Block for the rifles mag well for using a vise and the proper wrench for the nut. I noticed the nut is staked in two spots. How do I remove the staking so I can loosen the nut? I dont want to just try and torque on it with the wrench as I am afraid I could break the reciever. any help is appreciated.