DLC vs HARD CHROME
Frequently Asked Questions — Bolt Carrier Group Finish Selection
The steel underneath is the same. You’re choosing a surface.
// The Short Answer
These aren’t two different bolt carrier groups. They’re one group with two surface strategies.
Our polished DLC group and our Super-Stake hard chrome group are built on the same foundation: an 8620 carrier in the M16 full-auto profile, a C158 bolt that is shot peened, high-pressure tested and magnetic particle inspected, a 4140 phosphate extractor with a black insert, Sprinco springs, and the same 11.6 oz on the scale. Whichever you pick, the parts that determine strength and reliability are identical. What differs is the surface those parts wear, and each finish is genuinely better at something. DLC is harder and slicker, releases fouling better, and adds so little thickness it doesn’t touch your fit. Hard chrome is a proven plating with a long service history inside AR carriers, it can be reapplied to a worn part, and its bright surface makes an inspection actually informative. The most telling detail is that our DLC group uses chrome inside the carrier bore and gas key — because in there, chrome is the right answer.
// Two Coatings, Two Jobs
One is deposited as a vapor. The other is plated from a bath.
DLC — diamond-like carbon — is deposited in a vacuum chamber, a few microns thick. Published hardness figures run from roughly 1,500 HV for common hydrogenated grades up to several times that for the hardest, against roughly 800–1,050 HV for engineering hard chrome. Dry friction against steel is typically quoted around 0.05–0.15 for DLC. It is chemically inert, which is why carbon has a hard time bonding to it. Because it conforms to whatever surface it lands on, the substrate is polished first — that step is what turns a hard coating into a slick one.
Hard chrome is electroplated, and it is not the poor relation. A classic engineering reference puts chromium on steel at a coefficient of friction around 0.16, against 0.30 for steel on steel — roughly half. You will find vendor material claiming much worse for chrome; the honest position is that published friction figures vary enormously with test conditions, and that DLC is lower but not by the margin the most enthusiastic comparisons suggest. Chrome is also thicker, which means it has to be planned into the machining, and it can be stripped and reapplied to salvage a worn part — something a DLC coating does not offer.
The clearest evidence that this is not a contest is our own DLC group. Its carrier’s inner bore and its gas key are chrome-lined, with DLC on the exterior. A vacuum-deposited coating reaches what it can see; a plating bath reaches down a bore. Rather than insisting on one finish everywhere, the group uses each where it works best — which is also the answer to which one is better. Both, in different places, on the same part.
| Polished DLC (DLC+) | Hard Chrome (Super-Stake) | |
|---|---|---|
| Carrier | 8620, M16 full-auto profile | 8620, M16 full-auto profile |
| Bolt | C158 — shot peened, HPT, MPI | C158 — shot peened, HPT, MPI |
| Extractor & springs | 4140 phosphate w/ black insert · Sprinco | 4140 phosphate w/ black insert · Sprinco |
| Weight | 11.6 oz | 11.6 oz |
| Exterior finish | Polished, then DLC | Hard chrome |
| Carrier inner bore | Chrome lined | Chrome |
| Gas key | Chrome lined, OCKS hardware, staked | Phosphate, OCKS, hand-staked heavy duty, opening verified |
| Process | Vacuum deposition — reaches line of sight | Electroplating — reaches into bores |
| Thickness | A few microns — no meaningful change to fit | Thicker — planned into the machining |
| Hardness (published) | ~1,500 HV and up, by grade | ~800 – 1,050 HV |
| Friction vs steel | ~0.05 – 0.15 dry | ~0.16 (vs ~0.30 steel on steel) |
| Appearance | Black | Bright — wear and cracks read easily |
| Repairable | No — replace the part | Yes — can be stripped and re-plated |
| Best at | Fouling release, cycling consistency | Serviceability, inspection, proven service history |
// Questions We Get Asked
Why does our DLC group use chrome inside the carrier?
This is the most useful thing on the page, because it tells you these finishes aren’t rivals:
- DLC is a line-of-sight process. It’s deposited as a vapor in a vacuum chamber, and it coats what the source can reach. The deep interior of a carrier bore is not that.
- Plating goes where a bath goes. Chrome can be deposited down an interior bore, which is exactly why chrome-lined carrier bores and gas keys have been Mil-Spec practice for decades.
- So the DLC group uses both. DLC on the outside where it’s the better surface, chrome inside the bore and gas key where it’s the only practical one. Nobody has to choose a finish ideologically.
Which is actually harder?
DLC, and not marginally. Published figures put engineering hard chrome around 800–1,050 HV, while common DLC grades start near 1,500 HV and the hardest run several times higher. Both are far harder than the steel beneath them; the practical consequence is wear resistance on sliding surfaces rather than anything you’d feel on day one.
Which is slicker, and by how much?
DLC, but we’d rather be accurate than dramatic about it. Chromium on steel is classically cited around 0.16 against roughly 0.30 for steel on steel — chrome is already about half the friction of bare steel. DLC is typically quoted at 0.05–0.15 dry. Real: meaningful. Not real: the four-to-tenfold gap you’ll see in some marketing.
Which cleans up easier?
Both are dramatically better than phosphate, and DLC has the edge. Carbon bonds poorly to a hard, smooth, chemically inert surface, so on DLC most fouling wipes rather than scrapes. Chrome is close behind and the difference between them is far smaller than the difference between either and a parkerized carrier.
Why does the bright finish matter?
Inspection. Cracks, unusual wear patterns, and carbon tracking from a leaking gas key are far easier to see against bright chrome than against a black surface. If you or your armorer actually look at the bolt group on a schedule, chrome shows you what’s happening to it. This is the one place chrome clearly beats DLC.
Does either change how the parts fit?
DLC effectively doesn’t — a few microns means a part machined correctly before coating is still correct after. Hard chrome is thicker and has to be accounted for in the machining, which is routine for a manufacturer building to it but is a real difference in how the part gets made.
What happens when a finish wears through?
Both will show wear at high-contact points over a long service life; that’s normal, not a defect. The difference is what you can do about it. Chrome can be stripped and re-plated to salvage a part. DLC can’t be touched up in any practical sense — when it’s gone, you replace the component.
Does either make the group stronger?
No. Strength lives in the 8620 carrier and the C158 bolt, and those are identical between the two groups. A coating manages wear, friction, and corrosion at the surface. A finish over a poor bolt is a poor bolt with a nice finish — which is why we care more about what’s underneath.
Does either affect accuracy?
Not mechanically. Barrel and ammunition set group size. What a lower-friction surface contributes is consistency in how the rifle cycles across a string, which is shooter-facing — and on a precision rifle that’s the reason we favour DLC there, not a claim about the barrel.
Does the gas key differ between them?
Yes, and it’s worth knowing. The Super-Stake group’s phosphate key is hand-staked heavy duty with the staking opening verified and alignment checked as its own operation — staking works by displacing metal, and phosphate displaces where a hard plating resists. Both groups use OCKS hardware and both carry our laser-engraved index line.
Can either take the HMB bolt?
Yes. We offer the HM Defense HMB bolt in both configurations — black nitride and hard chrome — so a reinforced cam pin location and your preferred surface aren’t a trade-off. The matched radiused cam pin comes with it, laser engraved with our arrow index.
Which should I pick?
Since the mechanical parts are the same, choose on how you’ll live with the rifle:
- Polished DLC — precision rifles, suppressed rifles, and anyone who values the easiest cleanup and the most consistent cycling across a long string. It’s what we specify on our 6mm MAX® precision builds.
- Super-Stake hard chrome — high round count, duty and agency use, and anyone who inspects on a schedule. The bright surface and the gas key treatment are the arguments, and a serviceable finish matters on a rifle with a long working life ahead.
- Still not sure? Tell us the round count, whether you run a can, and who else handles the rifle. That decides it faster than a coating chart — and either way you’re getting the same carrier and the same bolt.
// What A Finish Cannot Do
A surface treatment is a surface. It is not the part.
- Neither makes the group stronger. See Q 08. Substrate steel, heat treat, and inspection do that, and they’re identical here.
- Neither shrinks your groups. See Q 09.
- Neither fixes a badly tuned gas system. An overgassed rifle is overgassed with any finish on it.
- Neither eliminates cleaning or lubrication. Easier is not never, and both still get run wet. The AR was designed that way.
- Published coating numbers are soft. Hardness and friction figures vary widely with chemistry, process, and test method. Treat the ranges on this page as relative position, not specification — including where they favour us.
// What You Get
Your bolt carrier group is identified on your build record by make, model, finish, and bolt configuration — with the headspace gauging result for that bolt against your barrel. Whichever surface you chose, the gas key was staked and index-marked, the cam pin carries our arrow index, and the group was function-checked before the rifle shipped. If you send the rifle in for a barrel change later, the bolt gets gauged again and the record is updated. If you want the other finish at some point, it’s a group swap and a headspace check, not a rebuild.
Two surfaces. One standard underneath.