Why does Steve hate laser porting so much?!

It’s no secret that I (Steve) am against laser porting barrels, but why?!

In short, it’s not a clean cut. Read along for a very boring explanation.

I feel that it is worth mentioning, but none of this article uses AI. When it comes to technology, I’m not too far from Ted Kaczynski. When it comes to the topic, I have such a strong opinion because I know enough about the topic to have an opinion.

First, we must cover some important aspects of metallurgy. Steel is not an element like iron, but it is iron with added elements for a specific purpose. For instance, carbon is the primary element for hardenability, silicon is used in spring steel for elasticity, chromium is the primary element for corrosion resistance and 10% chromium or more can qualify as “stainless” steel.

Why is this important?

This is important because the different atoms of elements (iron, carbon, chromium, molybdenum, etc) are liquified together, but as the steel cools, these atoms collide and form crystals. As the steel hardens and cools, these crystals develop into a grain not too different from how it is in wood, just arranged differently. The arrangement of these crystals, the grain of the steel, has different properties based on the arrangement of the grain. The steel is the same steel, but the grain is what gives it the desired property. If the steel is heated, these grains can grow in size and change properties. Remember that last part.

Similar to how the grain of wood is laid out depends on how tough it is. This is the same with steel. Lets talk about knife-making because I have watched a lot of Forged In Fire and I can associate the steps with each grain structure.

• - Lets say you get a nice piece of new billet steel straight from your supplier. Most likely, the grain structure is “ferrite” – it’s what will be nicely workable for that type of steel. What does Dave Baker do when he has steel? He throws it in the forge!

• - That steel is now glowing orange hot, heated above its critical temperature. This grain structure is “austenite”. It’s ductile and ready to be worked.

• - Your blade is done and is ready for THE QUENCH! It’s heated to critical temp and rapidly cooled in the oil. This is now “martensite”. Martensitic steel is very hard, which is why the file skates off it. It’s also very brittle because the grain structure could be considered chaotic. You rapidly cooled the steel without allowing the grain any time to adjust.

• - Time to fix your brittle martensite. You’re ready for the heat treat, or the tempering of the blade. Tempering the blade allows the grain to reorganize to a more desirable characteristic. Now that you’ve tempered your steel, you have “tempered martensite”, which is different grain structure than just martensite. This grain is what most blades are. Tempered martensite is still very hard with much less brittleness. As with life, everything is a tradeoff. You may lose some of that hardness, but your steel will be able to flex and rebound under tension without suffering a catastrophic failure.

These concepts about the grain and the structure is true for any steel. My butthole always puckers while color case hardening (CCH) because the goal is the same as above, and your part runs the risk of warping, the same as the blades on Forged In Fire. While doing CCH, I’m heating a part above the critical temp to austenite steel so the exterior can absorb carbon from the surrounding medium, then it’s quenched into martensite. There are many more grains of steel, but you can understand what I’m talking about for the most part.

Before we can talk about lasers, we have to talk about welding. Have you ever seen that surface oxidation after welding where it turns blue on an otherwise nicely polished part? That’s indicative of a heat affected zone, or HAZ. The HAZ is the area next to the fusion zone, which is where the metal from the filler rod is fused to the base metal. This heat affected zone will change the grain structure of the base material. TIG welding allows for very precise control of your puddle, has shielding gas, and is typically ran with a foot pedal to give micro adjustments on the fly. However, there is still a heat affected zone. You can minimize the HAZ by preheating the steel, watching your amperage, having a good control of your travel sped, etc. Lasers are no different.

NOW, LET’S TALK ABOUT LASERS

Lasers remove material by concentrating enough heat (heat = power) into a very tiny area, and enough heat to vaporize metal. When you see that bright plume of color where the laser is removing material, that can be from metal being vaporized into a gas and becoming plasma. As the metal is vaporized, the gas expands in size relative to the amount of metal, and ejects some of the molten metal out of the vaporization crater. This can be seen as the laser is operating. With this intense heat, a laser absolutely has a HAZ around the vaporization zone.

To put this in perspective: the focal point of a fiber laser can be 0.03mm and eject particulates about 2cm. if the focal point was the size of a 55gal drum, it would be like launching a particulate of the drum almost a half mile from the rapidly expanding gas.

This is the amount of power/heat we are talking about.

This launched material does not eject as a solid as soon as it is expelled from the vaporization area. This launched material hits the side of the area that was just cut, effectively re-welding it to the wall of the cut surface. This is called the “recast layer”.

A 2024 study of laser cutting processes from Bali, Indonesia (Yanuar, et al., 2024) used scanning electron microscopes and showed that fiber lasers have an inverse relationship between speed of the laser travel and the amount of the recast layer. With increased speed comes more molten material that gets recast to the nearby area, and a slower speed showed a larger HAZ but less recast slag. This article also showed that the pressure of the shielding gas affected it also, ranging from 2-29 bar. This is between 20-290 PSI, with higher pressures more effectively evacuating material and cooling it before it is recast.

In this article, the lasers that were used were industrial lasers with either oxygen, argon, or nitrogen as a purge gas. Doing some research, Thermal Processing Magazine shows (Bowe, 2026) a recommended purge gas setting of 37.5 SCFM (2,250 SCFH / 60 = 37.5 square cubic feet per minute) for 1/8 inch thick material, which I figure is relatively close to the thickness of a pistol slide or barrel. Yanuar (2024) showed that even with this purge gas, there was a thick recast layer when inspected under a microscope.

I know some laser defenders (pronounced /sɪmps/) will say that this is negligible because it has to be viewed under a microscope. Yes, when the focal area of a laser is measured in microns and the grain is measured in micrometers, I don’t think you’re going to accurately measure the recast layer and grain structure by squinting really hard.

Now we can talk about the HAZ. “Experimental study of heat affected zone for CO2 and fiber laser machining of SS 316L material” (2023) shows that the HAZ of a fiber laser can be measured in TENTHS of a millimeter, exponentially larger than the size of the focal point of the laser. The HAZ changes the properties directly around the port from tempered martensite to austenite immediately around the vaporization zone, and possibly bainite and perlite, niether of which grain structure are has hard or tough as the tempered martensite of the original material when referencing a barrel. in theory, you could retemper the barrel, but at which point in the barrel making process was the original stock tempered? if you heat treat it again, will you have a dimensional shift? do you even know how you would measure dimensional changes? laser operators don't, or they wouldn't be porting barrels with a laser.

“The challenges of laser cutting: Overcoming some common obstacles” in The Fabricator (2002) makes some good points that still hold true almost 25 years later. Part geometry matters, with corners holding more heat and more subject to thermal runaway and blowouts. Wollenberger notes (2002) that the recast layer is much more prone to initiating a crack, and with a HAZ having mechanically changed properties (grain structure), the crack is initiated at the recast layer and extends through the HAZ to the base material.

Reger Laser (2025) explains “stress” in the metal, stating “Thermal stress is one of the quiet killers of precision in laser cutting. You design a perfect part, run it on an accurate machine, and the piece comes off the table warped, bowed, or out of tolerance. The cause is heat: the laser melts a narrow line, the metal around it heats and cools unevenly, and that uneven movement leaves stress locked into the part.”

Bach (et al., 2023) shows that dross formation (recast layer) can influence the lifespan of a 304 stainless part. This article demonstrates a 23-68% reduction in lifespan of a the part due to cracking when compared to a polished or machined part.

I feel as though I can continue on for quite a while about this, especially when I haven’t touched on another phenomena of laser cutting, and that is a cone shaped, tapered hole. I have seen several instances of holes that taper inward, making a suboptimal port.

Lasers have gained much popularity, they’re very cheap ($4,000) for a hobby laser when compared to a CNC ($20,000 for an old used Haas), and are much faster than a conventional mill when both an old Bridgeport and a hobby fiber laser are about the same price. The advantage to the fiber laser when it comes to machining is that a laser can cut a part geometry that a mill cannot, although the sharper corners are subject to more heat at stated above. When it comes to a part that has repeated thermal cycling at pressures around 38,000 PSI, I believe that the sharper edge is wielded by the mill.

A mill removes material by a mechanical cut, and there is nearly zero heat imparted into the part when adequate cooling is used. A mill has very controllable part geometry with a rigid setup, with absolutely zero possibility of “coning” and leaving a cone shaped hole (unless your cutter breaks every single flute). The edges produced by a mill have no sharp edges for hot spots when venting gas, which lead to erosion, and the surface finish of the part walls are nearly perfect unless there is gross chatter. When crack propagation is a possibility, I will always hedge my bets in the safest manner possible. This is why I use a mill for all ports.

My gripe is not so much with a fiber laser itself, and I have a few. My gripe is with the people that operate these lasers. These people refuse to believe facts when confronted with them, most do not understand metallurgy and have no intent to, and they just want to use their laser to burn out parts of metal without understanding the ramifications. When large chunk ports are done by fiber laser, I highly doubt that they have a lathe because they’re not machinists or gunsmiths. They’re laser operators. I have seen several examples of chunk ports done by laser while I still see rifling beneath it. This is absolutely unacceptable and inherently decreases accuracy.

I don’t want my ports cut by a laser. Period. If I don’t want it, I’m not going to give it to my customers. I’m not sying that everyone’s ports will fail, or your barrel will blow apart. I am saying that if you do not properly dress your ports, you will suffer from performance degradation, and that is inarguable. I use several machines for porting, including a lathe and a mill. I do have a laser, and I love it. A laser has a place in a modern machine shop, but it’s not for use on a barrel.

References

1) Yanuar Rohmat Aji Pradana, Chandra Hairat Abdul Rahman, Raka Afrianto, Aminnudin Aminnudin, Wahono Wahono; Recast layer and HAZ formation from laser cutting of SUS 304 plate under cutting speed variation. AIP Conf. Proc. 26 March 2024; 3110 (1): 020057. https://doi.org/10.1063/5.0204931

2) Bowe, Don 2026 https://thermalprocessing.com/wp-content/uploads/2019/03/0319-AirProducts.pdf

3) Tukaram Sargar, Aniket Jadhav, Nitish Kumar Gautam, Experimental study of heat affected zone for CO2 and fiber laser machining of SS 316L material, Materials Today: Proceedings, 2023, ISSN 2214-7853, https://doi.org/10.1016/j.matpr.2023.08.322

4) The challenges of laser cutting: Overcoming some common obstacles. (2002, March 13). Thefabricator.Com; The Fabricator. https://www.thefabricator.com/thefabricator/article/lasercutting/the-challenges-of-laser-cutting-overcoming-some-common-obstacles

5) Reger Laser, (2025, October 21). Thermal Stress in Laser Cutting: 6 Proven Fixes. Reger Laser. https://www.regerlaser.com/blogs/understanding-thermal-stress-in-laser-cutting/#what

6) Bach, J., Zeuner, A. T., Wanski, T., Fischer, S. C. L., Herwig, P., & Zimmermann, M. (2023). Influence of the Dross Formation of the Laser-Cut Edge on the Fatigue Strength of AISI 304. Metals, 13(3), 624. https://doi.org/10.3390/met13030624-