I put some sight black on the end of the gas tube and took the bolt out of the bcg and the charging handle out of the receiver.
When I tip the barrel down to the ground the bolt will freely slide all the way at 35-40 degrees tilt. So it seems in spec.

But at a shallower angle you can feel and see it catch on the gas tube and after 20 repetitions you can see the side of the gas tube opposite the ejection port has some shine in it where the sight black paint has rubbed off.

24" bbl rifle length gas. Old yhm alum free float bbl nut with the holes for gas tube

Would like it to be an "accuracy gun"
(Haven't shot it yet)

Does it shoot and function? What bcg and gas tube is it?

Look at this logically...

If the bolt is returning to battery when you charge it, the interference is minimal and will not affect the gun's function in that direction.  But since you haven't shot it yet, if the interference is enough, it may prevent the BCG from fully cycling back to reset the hammer and/or lock back on the last round.  I do not believe this interference will affect the accuracy of your rifle.   But if you have OCD like me, the gas tube may not be aligned completely between the gas block and the upper receiver.  You may need to see if the gas block is slightly rotated where the gas tube is not on top dead center.  Or the barrel nut may be slightly over rotated which is pushing the gas tube off of top dead center.  A small adjustment may be necessary.

I think this may be the case.
Shouldn't loosen it once tightened though right? I can't get to the "next hole".

I saw a post here that tension on the gas tube by the key caused a weird cold bore shot pattern where the first round was 4-5 inches high and rest would start to walk down as the shots increased. Which made me think about that. (That was more fore and aft placement of the tube and tension though)

It's an old bushy hbar upper with semi auto bcg  that i rebarreled to 6.5g

You're right, you can't just back it off and leave it.  But you can completely loosen the barrel nut and re-torque it.  If you can get it aligned and you're between 30 and 80 ft-lbs, you're good.  If you can't get it aligned in that range then you might need shims, or you can lap the receiver.  Unfortunately you'll have to remove the gas tube from the receiver to do this.  Hopefully, since you have a rifle length and plenty of dwell, you can simply loosen the gas block and back it out without removing the tube from the block (which is a PITA).

With the black paint on gas tube


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After sliding the bolt carrier back and forth a dozen times or so.

Some running on top and left of tune (as it sits in the pic).



It slides into place when doing the angle test - but obviously rubbed a little- so I nudged it with the end of a plastic tooth brush down and to the right a little.

It now slides even faster and smoother with what feels like no rubbing.

So... I guess I jimmies it into a better alignment. Haha.  Not pretty but this is an el cheapo setup.

The gas tube should not be touching either the lugs in the hole in the upper or the barrel nut.
It is not unusual to need to tweak the tube’s alignment.

This is what I was about to post.
Your issue is very minor and easily fixed.