How do you hide uneven gaps around railing posts set in concrete?

I've used the sleeve trick on a couple jobs where the concrete guys set my anchor bolts without me there, and it reads fine as long as you commit to it. The mistake people make is sleeving only the wonky posts. If two collars show up out of nowhere it looks like a patch job, but if every post gets one, same size, same height off the step, it just reads as part of the design. Base collars on rail posts are honestly a classic detail anyway, so nobody's going to question it.

For fit, leave a little clearance. I aim for a gap about the thickness of a nickel on each side so the sleeve drops on over paint without dragging. If you go snug you'll be fighting it on install and scratching the finish you already shot. Tack the sleeve in two or three spots, eyeball your gaps all the way around, then run a small continuous bead at the bottom only and dress it with a file so it looks like a deliberate collar instead of a repair. A thin line of paintable caulk at the top edge hides the joint if you're worried about it reading as an add-on. One thing I'd do before final welds: with everything tacked up, run your spacing checks on the pickets or circles. Someone mentioned the 4 inch sphere rule upthread and that's a real requirement for guards in the US, so easier to catch a wide gap now than after the finish is on.

Also, a few millimeters off on tubes somebody else set is a good outcome. Around here it's ussually an inch, not a few mm, and the sleeves are the difference between a redo and a Tuesday.

This is kind of what I did on a little porch rail for my sister, except I just lived with the tiny lean becuase I didn't know about the collar idea. Now I'm tempted to go back and add them to all the posts like you described. One thing I can't picture though, do you weld the collar on at the very bottom where it meets the concrete, or up higher on the post? And how do you keep from burning the paint off the tube while you're doing those little tack welds? I'd probly end up with scorch marks everywhere and have to repaint the whole thing.

Following this one close because I'm in a similar spot, just with a gate frame instead of railings. Only mine are off by more like a quarter inch and I figured the whole thing was junk until I saw this thread. One thing I'm stuck on, the concrete at my place is sloped for drainage, so the bottom of any sleeve is going to sit tilted. Do you trim the collar bottom at an angle so it seats flat, or just let it ride and fill the low side with caulk? I keep overthinking it and cutting cardboard templates at this point, which probably says something about me.

One thing I'd add, drill a small weep hole in the bottom of each collar before you weld 'em on. Water pools in those things otherwise and rusts from the inside out, especially anywhere that gets snow or sprinkler overspray. I learned that the hard way on a deck rail, had one split at the seam after a couple winters.

Also, do all your filing and touch-up paint before the final caulk line, cause the caulk won't stick to fresh paint the same way and it'll peel later. Been there.

Update: railings are on and done. Took the advice about sleeving every post, not just the two crooked ones, and that made all the difference. They read as intentional, my cousin actually thinks I planned it that way. Also drilled weep holes in the bottoms before welding like someone here suggested. Fit them snug with a rubber mallet and the paint survived fine.