Question. On the 600mm .25 barrel is this end supposed to be able to unscrew to attach a moderator? I believe I got one with the gun in the box (just a hollow tube) one side threaded and one size looks to be the .25 caliber size. I cannot got the life of me unscrew this end cap piece tho even with a rubber lid opener to help. So looking for input here. Didn’t wanna bust out the vice grips and Knick my new gun up and still not succeed.