lonewolf -
My experience with LMF browner has been very good. The following is a checklist of things that might be causing some trouble:
Polishing - The browning job will only be as good as the polishing job. The parts should be polished bright with wet-or-dry paper wrapped around a hard backer, such as a file. Start with coarse paper (220 grit is usually enough) and finish with fine paper (400 grit is enough).
Applying solution - Avoid rubbing the solution onto the polished metal; just wipe it on with a long, even stroke. Too much rubbing back and forth will cause a layer of metallic copper to be deposited on the surface, which can retard the browning action. Just swipe it on once, and resist the urge to scrub it into the metal.
Carding between coats - You mentioned using a "synthetic" steel wool. I am not sure what this is, but if it's an abrasive pad, you may be scrubbing the browning off as fast as you're putting it on. Use real steel wool. The grade is not too important. I use steel wool scouring pads, bought at the grocery store.
Number of coats - The parts will normally be gray colored for the first pass or two. It usually takes me 6 or 8 coats to get the depth of color I want. This can vary with the type of steel used. Sometimes, if I am having trouble getting the browning to "take," I apply two or three coats and allow them to rust without carding between passes. This usually gets the browning started, then I can proceed with the remaining coats, with carding between.
Humidity - I live in south Louisiana, where the ambient humidity is usually pretty high, and we don't have a problem getting things to rust, including roofs, automobiles and garden tools. If you are in a low humidity area, you may need to build a damp box, which is nothing more than a wooden box big enough to hang barrels in, with a water vapor source, such as an old electric coffee pot, in the bottom and a light bulb to raise the inside temperature so that the water vapor doesn't condense on the barrels and parts.
Hope this helps,
Bill