NP3 CARRIERS
Frequently Asked Questions — Bolt Carrier Group Finishes
Not harder. Slipperier — everywhere.
// The Short Answer
Every other finish we offer answers wear with hardness. This one answers it with lubrication.
A bolt carrier group runs steel against steel, hot, under pressure, in its own combustion residue. Hard chrome and DLC address that by putting a harder surface on the part than the steel underneath. NP3 is a composite — sub-micron particles of PTFE locked inside an electroless nickel matrix — so the coating carries its own dry lubricant, distributed through its full thickness rather than applied on top of it. Wear the surface and you expose more PTFE instead of using it up. The second difference gets discussed far less and matters just as much: NP3 is deposited chemically rather than electrically, with no current and no line of sight, so the inside of the carrier bore and the inside of the gas key plate at the same controlled thickness as the outside of the carrier. That is not a claim any other finish on our shelf can make in a single operation.
// Why It Matters On A Carrier Group
A dry lubricant that plates like a plating — and reaches the surfaces you can’t.
Conventional electroplating, hard chrome included, is driven by electrical current, and current does not distribute itself evenly over a complicated part. It concentrates at edges and starves in deep bores, so thickness follows geometry unless the shop builds conforming electrodes to correct it. DLC has the opposite constraint: it is applied in a vacuum and is fundamentally line-of-sight, coating only what it can see. That is why our polished DLC+ group uses chrome inside the carrier bore and gas key — two finishes on one part, because one of them cannot get down a hole.
NP3 is autocatalytic. The deposition is a chemical reaction occurring on the part surface itself, not a current path, so every wetted surface plates at the same rate. A blind bore, a lug recess, a thread root and a flat exterior all come out at the same thickness — and that thickness is held to two ten-thousandths of an inch, which is what makes the process viable on a part with headspace consequences.
The payoff is not a harder carrier. It is a carrier that is lubricated in the places you cannot reach, cannot see, and cannot easily clean. That is also why it does its best work in dust and salt air, where oil is a liability because oil holds grit. The finish is insurance against the lubrication that ran out, burned off, or was never applied correctly.
| What the coating is | As applied to a Second of Ten carrier group |
|---|---|
| Coating type | Electroless nickel–phosphorus with co-deposited sub-micron PTFE — a true composite, not a topcoat |
| Specification class | SAE AMS 2454 — electroless nickel codeposited with PTFE |
| Deposition method | Autocatalytic — no current, no anode, no line of sight |
| As-plated hardness | Rc 48–51, measured on the nickel matrix |
| Lubricity | Self-lubricating dry film — fresh PTFE exposed as wear occurs, for as long as the coating is intact |
| Thickness control | Held to within .0002″ — two ten-thousandths of an inch |
| Corrosion resistance | Standard NP3 exceeds 250 hr salt spray at .001″; NP3 Plus published at 1,000+ hr per ASTM B-117 |
| Appearance | Satin gray, non-reflective — a light surface reads wear and cracking |
| Reversibility | Strippable with no effect on the base metal — the part can be re-plated |
| Surfaces coated | Carrier OD and ID · gas key bore · bolt · cam pin · firing pin |
| Where it is applied | By the process owner, to their specification — we do not plate in-house and do not claim to |
// Questions We Get Asked
What is NP3, and what is it actually made of?
Two things that normally do not go together, deposited at the same time. The process is aerospace work first and firearms work second — it falls under SAE AMS 2454, and the plating house that owns the NP3 designation has been running electroless nickel/PTFE on rotorcraft components since 1986.
- The matrix: electroless nickel–phosphorus. It supplies adhesion, hardness and corrosion resistance. The phosphorus content is where most of the corrosion resistance comes from.
- The lubricant: sub-micron particles of PTFE, suspended in the plating bath and locked into the nickel as it builds — distributed through the full thickness, not layered on top.
- Why that distinction is the whole point: a lubricant sprayed or dipped onto a surface is a wear item. Once it is worn through it is gone and bare metal is what is left. In a composite, wearing the surface simply uncovers more of the same material.
What’s the advantage on a carrier group specifically?
The carrier runs in the receiver, the bolt runs in the carrier, the cam pin runs in the raceway. Every one of those is a sliding steel-on-steel interface, and NP3 puts a dry lubricant on both halves of it — including the carrier bore and gas key bore, which you cannot reach, cannot see, and cannot easily clean. Carbon and unburned powder also have far less to adhere to on a dry surface than on an oiled one.
How hard is it?
Rc 48–51 as plated, measured on the nickel matrix. For scale, unhardened receiver and extension steels commonly sit near Rc 32, and AR500 armor plate is around Rc 51. It is a hard surface by any ordinary standard. It is not the hardest surface we offer, and that is deliberate rather than accidental.
Chrome and DLC are harder. Why choose the softer one?
Because hardness is a specification, not a score, and the right value depends on what the part runs against. A widely held view in the trade holds that a very hard bolt running against a much softer barrel extension can act on the extension lugs rather than the other way round, and that a mid-hardness surface is a gentler pairing. That is a reasoned industry position, not data we have generated, and plenty of hard-chromed bolts have gone a very long way without trouble. NP3 is not chosen because it is hard. It is chosen because it is slippery, uniform and corrosion resistant at a hardness that is more than adequate.
Does this mean I never have to lubricate it?
The coating is a true dry film lubricant and the process owner states it can be run without additional lubricant. Our position is more conservative: we specify lubrication per the manual on every carrier group we sell, regardless of finish. What NP3 buys you is not the elimination of lubrication. It is what happens when lubrication runs out, burns off, or was never applied correctly in the first place.
What difference does it make to cleaning?
A meaningful one, and it is the benefit owners report first. Fouling needs somewhere to adhere; on a dry, PTFE-bearing surface it largely does not have it, so deposits stay loose rather than baking on. In most cases the carrier wipes down with a cloth. That matters more than it sounds, because scraping a carbon-welded carrier is itself a wear event.
How corrosion resistant is it, really?
Standard NP3 is published as exceeding 250 hours of salt spray, and NP3 Plus at 1,000+ hours per ASTM B-117. Read those carefully — both are quoted at a coating thickness of one mil, and a carrier group is plated far thinner than that because a mil of build-up on a dimensioned part is not acceptable. The lab figures tell you the chemistry is genuinely corrosion resistant. They are not a service life. One characteristic that does carry over: where the coating is perforated, corrosion shows no tendency to migrate underneath it.
What does it look like, and can I inspect it?
Satin gray and non-reflective — lighter than phosphate, duller than bright chrome, nothing like black DLC. The inspection advantage is the same one we credit hard chrome with: a light surface shows you things. Carbon tracking, galling, a lug bearing unevenly, a crack propagating from a lug root — all of it reads more clearly against pale gray than against black.
Does the coating affect headspace?
It adds thickness, as any coating does — but a small and predictable amount, held to within .0002″, and deposited evenly rather than heavily on the edges and thinly in the bores. That predictability is what makes it usable on bolts and carriers at all. On our side, headspace is verified on the finished, coated assembly and recorded. We do not check it before plating and assume it survived.
If it wears, can it be redone?
Yes. NP3 strips without affecting the base metal, and the part can be re-plated or refinished in something else. That puts it in the same serviceability category as hard chrome, and on the opposite side of the line from DLC, which cannot be stripped and re-applied. For a customer expecting to keep a carrier group for decades, that is a real consideration rather than a footnote.
How is this different from a nickel boron carrier?
Both are electroless, so both plate uniformly — that much they share. After that they diverge on chemistry. Nickel boron uses boron where NP3 uses phosphorus, and carries no PTFE. It is harder, commonly cited near Rc 62. What it gives up is corrosion resistance, which comes largely from phosphorus content, and self-lubrication, which it simply does not have. They are not the same product with different marketing.
NP3, hard chrome, or DLC — how do I choose?
Start from what does not change. Across all three options the mechanical package is the same: the same M16-profile carrier, the same shot-peened, HPT and MPI Carpenter 158 bolt, the same springs, the same weight. You are selecting a surface, not a different carrier group — and certainly not a different group size.
| Finish | Its strongest claim | What it gives up |
|---|---|---|
| NP3 | Self-lubricating composite; uniform on every internal surface in one operation; corrosion resistant; strippable | The hardest available surface — it is the softest of the three |
| Hard chrome | Very high hardness and abrasion resistance; bright and highly inspectable; strippable and re-platable | No inherent lubricity — it wants oil |
| Polished DLC+ | The hardest and lowest-friction surface of the three; polished first because DLC is conformal | Line of sight — internal bores require chrome, and it cannot be stripped and re-applied |
Will an NP3 carrier group shoot smaller groups?
No, and we won’t imply otherwise. A carrier group finish governs friction, fouling behavior, corrosion and wear. Group size is governed by the barrel, the chamber, the barrel-to-receiver joint, the ammunition and the shooter. Everything on this page is a durability, reliability and maintenance argument. None of it is an accuracy argument.
Isn’t Robar out of business? Can you still get NP3?
This confuses a lot of people, so it is worth stating plainly. Robar was the gunsmithing business that took in customer guns, and it is indeed closed. Robar never applied the coating. NP3 was and is a process of Coating Technologies LLC, a plating house serving industrial, aerospace and defense customers, and the coating work always went there. The gunsmith closing did not close the process.
// What NP3 Does Not Do
A finish reduces friction and corrosion. That is the whole of its job.
- It is not the hardest finish we offer. At Rc 48–51 it sits below hard chrome and well below DLC. If abrasion at high round count is your governing condition, we will point you at one of those instead.
- It is not an accuracy feature. See Q 13. No claim on this page bears on group size.
- The published salt spray figures are laboratory figures at .001″. A carrier group is plated much thinner. Treat those hours as evidence about the chemistry, not as a service life on your rifle.
- Self-lubricating is not maintenance-free. We still specify lubrication per the manual. The dry film is a margin, not a substitute for the manual.
- It is a coating, and it can be destroyed by the tools people reach for. Its lubricity lasts as long as its integrity does. No abrasive pads, no wire wheels, no prolonged soaks in strong ammonia-based solvents. In normal service it should not need any of them.
- We do not plate in-house. NP3 is applied by the process owner to their specification. What we control is component selection, fit, assembly, headspace verification and the record — and we do not represent someone else’s process as ours.
- It will not fix a mis-specified rifle. A finish does not correct overgassing, a loose gas key, or a bad barrel extension fit.
// What You Get
The finish is inspected and the assembly is measured, not accepted on the label. The complete carrier group is NP3 finished throughout — carrier OD and ID, gas key bore, bolt, cam pin and firing pin — on a shot-peened, HPT and MPI Carpenter 158 bolt, with the gas key torqued, staked, and carrying our laser-engraved screw index line. Headspace is verified on the finished, coated assembly. It goes on your build record with the carrier group and bolt identified, the finish named, and the person who did the work initialled. The coating is someone else’s process. The measurement is what we’ll stand behind.
Lubricated where you can’t reach. Measured before it’s trusted.