M copper tubing is 'brittle' and heating it till it changes color will soften it to be workable though some M type tubing is alloy with other metal and not just hard drawn copper. Also I would drill the hole through the copper before cutting it short so as to save hand/finger danger. A quick 10 minute dip in vinegar will remove oxidation or the sandpaper works ,as will plumbers flux just prion to soldering. I always solder connections,even crimped, for best maintained ,low resistance, to be maintained as high current causes less heating/cooling to eventually loosen the connection and the old problem of dissimilar metals having corrosion when in contact.