Is it easier to remove the barrel first before fitting in a sash clamp ?

As I find that trying to keep the gun in postion whilst compressing the spring is awkward and can mark the gun as the compression gets greater, sometimes i find the gun wants vear left or right - Gas struts I usually send to a professional - Removing the spring i find is easier.

What do you guys use to protect the guns surface when compressing ?

Cheers