Front sight filing

I have no more vertical adjustment and plan to file the front sight down slightly. What product is recommended after to reblacken the front sight post?

First, what gun?

On one of my conversions. It’s bottomed out and I have to aim high 9 ring

Something is wrong with that statement...your rear sight needs to move the direction you want the group to move.
Are you sure you don't mean to say the rear sight is as high as it will go?

Sorry haha. I aim low 10 ring/ high 9 ring at 6 o clock. But there is no more adjustment to move up.  What product can I use to finish the front sight after filing?

Rear sight corrections move in the direction that you wish to move the bullets impact. So if you are shooting low and can move your rear sight you would move it UP.

So you have plenty of adjustment if you have the sight all the way down.

You are aiming approx. 1.8" from the center of the target and I believe the Nelson sights are 1 MOA per click which means you need to move the rear sight up 3-4 clicks at 50yds or 6-8 clicks at 25yds. - You never said what distance you were shooting at.

Just in case you described it wrong (or I misunderstood you) Here is a link to calculate front sight height adjustments, also use cold blue if you do need to file your front sight:
https://dawsonprecision.com/sight-calculator/

- Dave

I thought I was correct. Maybe I just said it incorrectly when I said bottom out. Now I’m second guessing myself. I’ll have to pull it out of the safe this evening. I was going off of my notes. I know my 50 yard adjustment is typically the last click, so either way it’s close

As for blackening the sight, if it's steel Cold Blue, Perma Blue or similar, if it's aluminum Aluminum Black. I've used Birchwood Casey products for both with acceptable results.

Pretty sure i was wrong. At 25 yards, center hold, with the adjustment all the way down, rounds impact a few inches high. So I don’t need to file the front sight, I need a taller one correct?

That is correct. I lowered my 1911 groups by epoxying a shim on the front sight. This has worked for a long time. Be sure  to raise the rear sight at least 10 clicks before you experiment with shims or try calculating the proper height. Never want a bottomed sight.

Move or adjust rear sight in the direction you want bullet impact to go. Move or adjust front sight in opposite direction you want bullet impact to go.

This may be useful in determining how much.
https://www.brownells.com/guntech/sight_correction_calculator/detail.htm?lid=13093