I say, send it back to HP and explain the condition, and odds are you'll get a shiny weapon safety checked back in no time!! BUT......
If the weapon cycle's fine and you just want to refinish it in a DIY method, here's a few tips:
On the poly stock:
-Sand down the stock LIGHTLY to even out the finish and to make the surface a bit more rough
-Head down to your favourite hardware store and pick up a can of Krylon Fusion polymer paint in whatever colour you like (I assume black will be the preferred shade, but I have seen OD green and sand work quite well)
-Spray onto the stock (once DETACHED from the weapon...gotta say that at least) while taping off the leading edges of the weapon (any face or edge that is not exposed while the gun is assembled). Follow the procedure on the can
Do that, and the stock will look shiny new 8)
Now, if the steel is discoloured and you need to re-blue the weapon, the BEST way for a home user is a cold-bluing method following these steps
-Disassemble the weapon
-Use a non-petrol based solvent to remove any oil, and remove any other plastic elements attached to the gun
-Mix a "citric stripper" compound to remove the majority of the bluing and leftover paint. This is achieved by mixing 5 packets or a citric Kool-Aide (unsweetened, cherry or fruit punch seems to have the most acid) to two tablespoons of water. Mix more or less as needed. Spread onto the rifle and let stand for about 5 to 10 minutes. After that, scrub the metal parts down and you will find that nearly all of the finish has been stripped away without any chemical fumes or scarring to the steel!!
-Using a hard felt dremel head and a #3 steel polishing compound, apply a moderate coating on the portion of the steel you are working and then directly buff out in a figure eight pattern ALL of the bluing. The steel compound might be a bit hard and could use with a little warming up (just stick it under an incandecent lamp for a few minutes and that should be MORE than enough). Now, you will have to work in a small areas to get a GOOD polish, but it's worth the effort to get a QUALITY job. Take care not to overwork one area, and to always keep the rotorhead moving and never leave it standing on one spot. Ever. This will mar the steel, even with a felt head.
-Finish off the polishing by coating the piece liberally in Brasso brand brass and soft alloy cleaner. Let the polish dry on the surface. Then buff in the same manner as the steel compound, but not as long. This gives a more finished appearance to the metal and a more even polish.
Now you are ready for a cold bluing!!!
You can find the cold bluing compound Brichwood-Casey's Perma Blue liquid gun blue at just about any sports hunting or firearms store (even China-Mart). A 3oz bottle ran me about $8. It seemed to have the best reviews and was the most common on the shelf. Also, the application process was pretty straightforward and only required a few items:
-Cold water and a decent tub to do the work (The shower worked perfect)
-000 Steel Wool
-Application sponges or rags (clean and free of any oils)
-A clean towel that you don't care too much about
-PPE (Personal Protective Equipment: Chemical Resistant gloves, eye protection and clothes you're not too attached to.)
-Aerosol-applied gun oil
-De-natured rubbing alcohol
Clean the gun of all impurities and dry it. Then, with a moist sponge, apply the bluing agent to the sponge and then onto the rifle, giving it a thin, even coat. Follow the instructions to let it sit for about a minute, and then rinsed the entire work surface with cold water.
After rinsing the work surface, begin to even the finish with a pad of 000 steel wool, working the grains that didn't get covered by the original solution. Now, this is where you begin to see the chemical reaction take place. The steel being treated will start to actually turn the minute you apply the solution, but the finish really doesn't begin to even out until the iron from the steel wool comes in contact. It's kinda cool actually!
Now, the bottle touts it as being a one-application finish. This simply is not true. But, after you dry, re-apply and repeat several (or in this case, seven) times, the effect is VERY good!
Upon the final treatment, let it air dry, then come back to remove the remainder oxidation with a slightly moist towel. Then, after drying the work surface, apply a layer of gun oil to the rifle and evenly wipe down the entire piece. After that, use an aresol based gun oil (I suggest RemOil) and shoot the entire work surface and let sit overnight.
In the morning, you will have perfectly blued steel that will look even BETTER than the factory finish!!
Then, reassemble the rifle in reverse order, lube all critical points, do a full points inspection and enjoy at the range!