View Full Version : How does the hardness of metal affect parking?

Stg 58
September 20, 2001, 22:13
I just parked a DSA reciever and a Dpms reciever and some misc G1 parts. the DSA came out a lot darker than the Dpms.Using brownells stuff.does this mean the Dsa is softer metal and dpms is harder.Also do most G1 and STG lowers come out lighter in color than barrel?I prepared both recievers at the same time and same method.Thanks

September 20, 2001, 22:48
Alot of variables here...
Hardness, of course does not equal strength, and lightness does not equal hardness.
Hardness, unfortunately, typically equals brittleness. (Okay, differing materials excepted...)
But, say in the case of Plow-steel, it's case hardened, and only the surface is hard, the core underneath yielding the strength of pliability.
The DSA is 4140 (chrome-moly)steel.
IMBEL, for example, is 1060(high-carbon)tool steel).
FWIW- I believe the DPMS is 4140 as well.
But I believe that the through-hardening that DSA does( to a 30-40 RC hardness) is known to be hard to achieve without warping the item in question.

All of this This will affect the ion-exchange in parkerizing,( iron vs. nickel vs. chrome content vs. hardness..).
That being said, I presume that you had sandblasted Both receivers (for some reason?) before re-parkerizing?

Stg 58
September 20, 2001, 23:54
Hi dirtfarmer,

Sandblasted both at the same time.Same grit and all.Did not like the paint like finish of the Dpms and wanted to fix some scratches left by installing the locking shoulder on the DSA. The DSA refinished almost to original color/darkness which really surprised me.i think the Dpms steel is harder.I tried to enlarged the pivot hole with a drill and it would hardly cut the metal.so is it harder will park lighter or harder will park darker?

September 21, 2001, 09:18

Harder will park lighter. Receivers will generally park lighter than barrel, carrier and bolt in most cases, and will show some minor color variations and in some cases, quenching lines.

September 21, 2001, 10:33
My observations(FWIW):

-the more coarse the blast media...the darker the park
-the harder the metal for any given blast media, the lighter the park

conclusion, the size of the 'dents' helps determine color.

Would junctions of different hardness metals be less obvious with a very fine blast finish? I dunno...anyone tried something really fine? I wonder if you used rough media on the hard part...and lighter media on the soft metal if you could match them better. Oh heck, I don't really care.

Oh, one advantage of finer blast media is the finish seems to be more scratch resistant than rougher media.

September 21, 2001, 21:29
if you look at Imbels or Entreprise receivers the spots that are hardened are darker. I think the harder the darker thats why bolts and hammers and the really hardened parts tend to be almost black. and you can tell the real hard metal when sandblasting because sparks will fly when the sand hits it! jmho :D