Firearms Nitriding & Black Oxidizing (Gun Bluing) F.A.Q.

Firearms Nitriding & Black Oxidizing (Gun Bluing) F.A.Q.

Firearms Nitriding & Black Oxidizing (Gun Bluing) F.A.Q.

Important Information: 

  • Please do not ship us an assembled/complete firearm for any reason! We are not gunsmiths. We cannot disassemble your firearm for processing. If we need to see your firearm, you may walk in with your firearm and consult with us before committing to disassembly. Do follow the law as required such as obtaining an STATT (Short Term Authorization to Transport) before bringing restricted or prohibited firearms to our shop.
  • Some of the following information in this FAQ is based on feedback from individuals whose firearms and firearm components we have treated, so some information may be anecdotal.
  • We offer this service at your risk. If we make a mistake, we will do what we can to make it right, but please ensure parts are available in the open market should any unforeseen problems occur. Our Liability Statement is here.

Note: The following information is tailored towards firearms. To learn more about our processes in general, see our Articles here.

Information Applicable to both Nitriding & Black Oxidizing

Do you have a Business Firearms License (BFL)?

Yes, we hold a business firearms license (BFL), allowing us to process non-restricted, restricted and prohibited firearms. We are licensed as “gunsmiths” only. We do not manufacture, sell, buy, store, change classification of, or transfer ownership of firearms.

How should I prepare my firearm components for shipment?

  • Fully disassemble firearms to the greatest extent that you or your gunsmith reasonably can. Shipping only the steel components that need our services.
  • It is important to remove any springs in components being nitrided (e.g. trigger springs, detent springs, ejector springs) as the nitride process temperature is 1055°F and will ruin the springs elasticity. The black oxidizing process is more forgiving in this regard as the process temperature is 285°F. In our experience, black oxidizing does not harm springs. You may wish to black oxidize items with difficult to remove or non-removable springs.
  • Separate orders into nitride and black oxide if both services are needed. Include a list of all individual parts and a total parts count for each process. You should count and take pictures of everything laid out before packaging. Upon receiving your order, we will count and lay out all the pieces and photograph them. We ship what we receive.
  • Pack your order carefully and include a complete packing list of all individual parts. Ship via Canada Post to: 9531 194A Unit 4 Street Surrey BC V4N4G4, following all legal requirements for shipping firearms. See Canada Posts firearms shipping guide here.
  • Please include a prepaid Canada Post return label.

How long have you been Nitriding & Black Oxidizing firearm components?

We have been nitriding firearms since 2010, and black oxidizing firearms since 2015. We have been nitriding & black oxidizing parts for manufacturers for many years. Processing large volumes of newly manufactured parts is different from processing small quantities of used parts for individuals. We have experience working with individuals, nitriding & black oxidizing many firearms, barrels, actions, and other components. We have done many jobs where the customer fully disassembled their firearm, sent in the pieces for nitriding, then reassembled that firearm to have a fully nitrided firearm! If you do this, don't forget to take “before” pictures! :)

Can you Nitride or Black Oxide a chrome lined barrel?

We have nitrided & black oxidized many chrome lined barrels. Nitriding will slightly change the color of chrome to a yellow/light-brown, just on the surface owing to the oxidizing step. We have heard no issues reported. Note: the chrome will mask the barrel bore, so there will be no nitriding in the bore if it is chrome lined.

Is surface preparation required?

By you? Yes: Ensure firearm components are free of fouling, especially the barrel bore. We can clean the outside of the barrel for nitriding/black oxidizing but we are not well equipped for cleaning bores, and we don't want to take responsibility for the bore condition. A light coating of oil after cleaning is acceptable. Note: You will need to clean your barrel bore again after you receive your order back from us.

By us? Yes: Surface prep is essential to attain the best aesthetic. For best results, we do a fine (100-120) grit aluminum oxide sandblast before nitriding or black oxidizing to achieve a matte/satin black finish. Both the Nitriding and the Black Oxidizing processes do not claim to produce the surface finish & aesthetic you might have in mind. The best method of getting a great finish that is repeatable, reproducible, and re-workable is to do a fine grit aluminum oxide sandblast before nitriding or black oxidizing. This is how we process mass-produced parts for OEMs and the one-off individual projects. If you have something truly special, we can work with you, but cost and risks will be higher.

How does Nitrera perform surface preparation?

We use several methods for surface preparation:

  • Acid Pickling Hydrochloric/Muriatic Acid: Usually only required to remove nickel and/or chrome plating. We have a small setup and use it sparingly. If you have a lot of plating to remove, you will need to send that out to a plating shop to be stripped.
  • Glass Bead Surface Prep: We use #13 glass beads (0.0017-0.0035” diameter) at 40-80PSI to clean and polish the surface.
  • Aluminum Oxide Surface Prep: We use 100-120 grit aluminum oxide blast media at 60-80PSI for surface cleaning. This yields the highest quality aesthetics, especially noticeable on barrels, action housings, and receivers.  

Do I need to remove the barrel from the action?

We have nitrided & black oxidized barreled and un-barreled actions with no issues, although brazing may potentially be revealed, and heat-treating salts may seep out from between mated parts at a later time.

Will brazing be affected by nitriding or black oxidizing?

We have nitrided & black oxidized barreled actions and barrels with brazed sights with no issues observed or reported, except where silver solder was previously covered by paint and is now visible. You may need to blacken the silver solder post-process.

Have any issues with nitriding or black oxidizing been observed or reported?

  • Silver brazing may become visible after nitriding or black oxidizing if previously hidden by coatings like paint.
  • We were concerned about nitrided shotgun barrels with non-removable ball detents in the magazine tube ring. After nitriding, the ball detents remained spring-loaded with no reported issues. However, these detents can sometimes be supported by rubber balls instead of springs, making outcomes uncertain. Be prepared for the possibility of needing to redo the ball detent after nitriding.
  • Some firearm components or hardened features thereof may see a reduction in core hardness owing to the nitriding process temperature (1055°F). For example, heat treated locking lugs of a receiver or bolt that take the brunt of the recoil or locally hardened wearing surfaces may be tempered while undergoing the Nitriding process. If you have information about the material chemical composition and/or heat treatment history of your firearm component, please share that with us so we can assess possible risks with you.

Does nitriding or black oxidizing fill in rust pits or otherwise hide defects?

No, neither nitriding nor black oxidizing process will fill in rust pits or hide defects.

What firearms or firearm components have you nitrided/black oxidized?

We have processed many tens of thousands of parts for manufacturers and individuals, including barrels, muzzle brakes, actions, bolts, barrel nuts, springs guides, magazines, optics mounts, gas pistons, pistol slides, and more.

We have nitrided & black oxidized firearms including the Webley Revolver MK1, Luger 9mm, Derya MK-12, Tikka T3CTR, Weatherby Vanguard, Remington 870, CZ 858, SKS, Robinson Arms XCR-M, Ruger 10/22, Glock pistols, and Remington 700 actions, Double Barreled Shotgun, and a Cowboy Action quick draw revolver.

Nitriding Specific Information

What does nitriding do to the surface finish? What does it look like?

The nitriding process forms a crystalline lattice structure of iron-nitride compounds inside of and at the surface that changes the surface finish. If the component is polished to a mirror finish then nitrided, it will then be a matte finish. It is possible to restore a pre-nitrided mirror finish post-nitrided mirror finish, with lots of extra polishing, may require subsequent black oxidizing port-polishing. The exact post-nitride surface finish depends heavily on the pre & post-nitride steps. Our standard process is known as “AL QP” (aluminum oxide + nitride + glass-bead polish). The AL QP finish is a satin finish. If you need a particular finish, we may need to leave that with you to polish at home or enlist the help of a gunsmith. See our Article on Q vs QP vs QPQ.

What materials can be Nitrided?

Any ferrous (iron-based) material, such as: Alloy steel (4140, 4340), steel (carbon steel, mild steel), stainless steel, cast iron.

We can nitride small/thin parts (extractors, pins, etc.), though very thin parts (cross-section of less than 1/16" or 0.0625" or 1.6mm) need careful handling & processing to avoid warping or embrittlement.

Caution: Nitriding stainless steels forms a very thin & very hard surface layer of nitride compounds. The surface layer will be 70-80HRC on top of the substrate/parent material. Since the core hardness of the stainless steel components is relatively soft e.g. 10-30HRC, and the transition from high hardness to low hardness occurs over a short distance of depth, the hard nitride layer is brittle and easily chips especially on corners/radii. Further, nitriding certain corrosion resistant stainless steels reduces the corrosion resistance. For further reading, see our Articles: “Nitriding Material & Component Selection” & “Nitriding Options (Q vs QP vs QPQ)

What materials cannot be nitrided?

We cannot nitride spring steels (though we can black oxidize them) or any component/assembly with spring steel attached (e.g., shotgun receivers with ejection and/or magazine tube springs) without the risk of changing the elasticity of the spring.

We cannot nitride non-ferrous metals such as aluminum, brass, copper, and titanium. Copper poisons our heat treating bath, and aluminum is softened and ruined.

What are the benefits of nitriding firearm components?

Nitriding improves several key properties of firearm components:

Corrosion Resistance:

  • Passes up to 400 hours Salt Spray Test as per ASTM B117 (material dependant).
  • Reduces the need for oils to prevent corrosion.
  • Far superior to hot or cold black oxide (gun bluing).
  • Resistant to corrosion caused by shooting corrosive ammunition.

Surface Hardness & Lower Coefficients of Friction & Adhesion:

  • Increases surface hardness to the level of “file hard” (55HRC for steel, 65HRC for alloy-steel, 70HRC+ for stainless steel).
  • Improves wear resistance and decreases throat erosion (results vary by barrel material).
  • Decreases friction and adhesion, increasing surface lubricity.
  • Provides benefits similar to moly-coated bullets without the extra cost, or a chrome-lined bore without the drawbacks of chrome buildup.
  • Significantly extends useful barrel life, with reports of doubling or tripling barrel life.
  • Allows for longer strings of fire before overheating.
  • Reduces bore fouling, enabling longer strings of fire while maintaining accuracy.
  • Makes action components run smoother, requiring less oil lubrication.
  • Prevents shotgun barrels from building up wadding plastic in the bore.
  • Simplifies cleaning barrels, bolts, actions, gas pistons, etc., due to reduced fouling buildup.

Increased Accuracy:

  • Slows fouling buildup, allowing longer strings of accurate fire between barrel cleanings.
  • Reduces friction and adhesion, slowing down barrel heat-up and enabling more accurate shots before needing to cool down the barrel.

Aesthetics:

  • Attractive black finish.
  • Removes & inhibits rust.
  • Long lasting finish. Nitriding is durable and not easily scratched.

What variation of nitriding do you offer?

We offer liquid salt bath nitrocarburizing as per AMS 2753.

Black Oxidization Specific Information

What does black oxide do to the surface finish? What does it look like?

The black oxide process forms a very thin layer of black iron-oxide that does not significantly change surface finish. The surface finish after black oxidizing is basically a black version of the pre-blackening surface finish. If the component is polished to a mirror finish then black oxidized, it will then be a black mirror finish. If the component is a matte (e.g. sandblasted) finish then black oxidized, it will then be a black matte finish.

Black oxide is very sensitive to surface cleanliness. Typically, we want to sandblast everything before black oxidizing. Black oxidizing a component in its original surface condition or finish comes with the risk that it may not come out looking as great as we want. If we do try to blacken it as-is, and it doesn't look good enough on the first run, the standard process of sandblasting to prep the surface is the best option for rework.

Although it is possible to blacken nearly any finish, it may be very difficult to remove the black oxide and restore that finish for reworking purposes. If you need a particular finish (e.g. polished), we can work with you, and cost and risks will be higher.

What materials can be black oxidized?

Most ferrous (iron-based) materials, such as: Alloy steel (4140, 4340), steel (carbon steel, mild steel).

Our particular salt mix/chemistry does not blacken stainless steels, high-silicon steels and iron.

What materials cannot be black oxidized?

We cannot black oxidize non-ferrous metals such as aluminum, brass, copper, and titanium. Copper and aluminum poison our heat treating bath.

What variation of black oxide do you offer?

We offer “hot black oxide,” which meets the following industrial standards: Mil spec mil-dtl-13924 (Class 1), AMS 2485, GE 70-43-12, ISO 11408.

We do not do cold black oxide or cold bluing/cold blackening. Cold bluing is applied at or near room temperature. It deposits a copper selenium compound onto the surface. This compound is not an acceptable substitute for hot black oxide as it does not look as nice, and can tend to be very smutty (easily rubs off onto hands and clothes).

Q vs QP vs QPQ Application Table

Q
Nitride & Quench
(Standard process)
QP
Nitride & Quench + Polish
QPQ
Nitride & Quench +
Polish + Quench
General
Case Hardened Surface to 55HRC+1

Reduces Friction & Adhesion by up to 60%

Black Oxide (Quench) for Corrosion Resistance & Aesthetics.
Same as Q, plus a Polishing step which restores the original finish, and increases surface luster.
Same as QP, plus reimmersion into the oxidizing (Quench) salt bath to further enhance corrosion resistance.
Price & Delivery
Lowest cost & fastest delivery
Marginal increase in cost & delivery time
Highest cost & delivery time
Surface Roughness (RA)2
≤32µin (0.8µm)

Nitriding can increase RA up to ~32µin (0.8µm) total
≤16µin (0.4µm)

QP restores RA to ~8-16µin  (0.2-0.4µm)

RA can be restored to ~2µin (0.05µm) by hand polishing or other means.
Same as QP
Appearance / Aesthetics
Deep matte finish

Some material may be aesthetically affected by brown/red iron oxides (particularly stainless steels and cast iron)
Satin Luster

Very high quality & consistent appearance from part to part & batch to batch.

Polishing removes brown oxides and other surface contamination & visible defects.
Same as QP but with further handling and processing there is decreased part to part & batch to batch consistency of appearance.
Corrosion Resistance
(Compared to Raw / un-Nitrided Material)
Carbon, low-alloy & tool steels: Tremendous increase3

Martensitic stainless steels: Moderate increase

Nodular irons: Slight increase

Precipitation hardened stainless steels: Unchanged

Ferritic & Austenitic stainless steels: Decreased
Carbon, low-alloy & tool steels: Same as Q

Martensitic stainless steels: Same as Q

Nodular irons: Same as Q

Precipitation hardened stainless steels: Reduced compared to Q

Ferritic & Austenitic stainless steels: Further reduced compared to Q
Carbon, low-alloy & tool steels: Potentially better than Q & QP

Martensitic stainless steels: Likely better than Q

Nodular irons: Same as Q

Precipitation hardened stainless steels: Likely better than Q

Ferritic & Austenitic stainless steels: Significantly better than Q
Best Choice
Any material needing surface hardness, yet surface roughness does not need to be <32µin (0.8µm), and corrosion resistance & aesthetics are not critical.
Surface Roughness (RA) of <32µin (0.8µm) required. E.g.: seal surfaces, cylinder bores, etc. 

Components with high-spec aesthetic requirements. E.g.: Firearms, tools, etc.
Same as QP 

Stainless steels if corrosion resistance is critical  

Everything else if the additional cost is worth it.

1 55-60HRC for Carbon Steels, 60-70HRC for Low-alloy Steels, 70HRC+ for Stainless Steels
2 Nitriding is not expected to increase surface roughness (RA) where the starting roughness is >32µin (0.8µm)
3 Up to ~400hr ASTM B117 salt spray test