The drift pin holds the end cap on. A wrench was made with an alignment pin that would insert into the hole towards the bottom of the tube and had support “wings” to loosen the tube. A drift can be used in place of the wrench taking care not to bugger the holes or kink the tube if it’s stubborn. A good idea to put some penetrating oil around the bottom of the tube and heat gently with a propane torch if it doesn’t want to come loose.
Once that tube is unscrewed the barrel will slide off and can be rotated 90 degrees and lifted free of the action bars. Then the bolt and action bars slide out the front of the receiver.
That.
Use the bold area technique, right at the tube's base - if this is the first time it's to be removed...
