DM is right (no surprise there). I would guess OP didn't break the seal first (b/c I've made this mistake before - and more than once
) When the trigger is pulled, advancing the plunger, the caulk could not go by the seal at the top, so it oozed past the seal at the bottom.
But I find most swing out rods are of insufficient length or inconvenient for quick and complete puncture. I keep a six inch piece of 12 g copper in my tool bag for this purpose.
How to make your caulking gun work:
1. Cut the tip off at the desired angle and depth. Many have little marks to guide you.
2. Insert rod or wire through the tip into the body of the tube to puncture the inside seal. Sometimes more than one 'poke' is required (TWSS).
3. Slowly squeeze the caulking gun trigger. Listen for air moving out of the tip and look for the caulk to fill the tip. If neither of these things happen - try puncturing the seal again.