How do I go about doing this. I put polishing compound on a bullet and shoot it out of the gun?

Why do you want to fire lap your barrel?

RR, Dave_G asks a good question.

If you've got a chrome lined barrel you'll be wasting good time and money you could spend for ammunition.  Chrome is too hard for firelapping to work.

On the other hand if your barrel is chrome-moly (regular steel) or stainless you can benefit if your barrel is brand new, heavily used (4k-6k rounds) or you're working on a precision rifle.

Fire lapping won't really help an everyday blaster.

You have the basic concept.  You basically impregnate bullets with a series of finer grits and shoot them at relatively low velocity.  Here are my basic guidelines for firelapping:

Don't use it with chromelined barrels.  Yes,it can work, but the results are not as good.

Don't use it with a new custom barrel.  Most custom barrel makers lap their barrels which is part of the cost.  If it doesn't shoot, you might want to consider it.

I'll firelap before I call Mr. Shilen, Mr. Lilja, Mr. Krieger, etc.

I have done several barrels using this method.  In all cases, accuracy has improved by a measurable amount (5-40%).  Barrel cleaning has also become easier, and velocity has dropped.  If you decide to fabricate your own, be sure to clean your dies, the compounds will scratch them.  Plan on spending several hours at the range to lap a barrel (the cleaning between the shots will take awhile).

As an alternative, I believe NECO offers both bullets and loaded ammo as a kit.

HTH.....SRM

David Tubb also has a complete loaded kit ready for firing.  You can get them at his website or Zedliker's has it and I've seen a few at gunshows.

If you load them yourself run them slow.  2400 ft/sec is good.