fred9x21 said:
Has the reciever been welded? Or heat treated? Metal that has been heat treated or welded on won't park evenly.
^^^ This.
When parts are heat treated, phosphating results will be spotty reflecting heat patterns in the parts. Sometimes grit blasting will remove residual oxide and the phosphate will "take" more uniformly, many times not. Sometimes acid pickling in hydrochloric acid or a blend of nitric/hydrochloric acids will pickle off residual oxides from the heating, but this is not recommended for the home refinisher. The dwell time in acid must be brief, and the subsequent rinses must be complete and effective in removing all acid. Finally, if the parts are hardened much above HRC 35 they should be baked at 350F for four hours immediately after rinsing to prevent hydrogen embrittlement of the parts.
If you tried to re-phos the receiver without stripping the existing phos finish, that will not work. For best results, you MUST strip the phosphate and reactivate the steel surface in order to re-phos a previously phosphated part.
If parts are pickled and then grit blasted (preferably steel grit, because the residual steel grit dust helps activate the surface of the part for phosphating -- same as initiating a new phosphate bath with CLEAN steel wool) it's the "best foot forward" for a uniform phosphate finish. If the parts are still spotty or striped following pickling, grit blasting, and phosphating, then it is what it is, and if aesthetics are important, a coating over the phos is the way to go.
Noah
