MJF vs SLS vs FDM Printing - Leber Lowers

We will take a small dive in to the benefits of HP MJF printing over SLS, as well as more common FDM printing!

HP MJF

Multi-jet fusion (MJF) is a type of 3D printing technology developed by Hewlett-Packard (HP). It works by depositing powder in layers, spraying it with a fusing and detailing agent, and then bonding it together with heat for each layer pass.

SLS

Selective laser sintering (SLS) is an additive manufacturing technique that uses a laser as the power and heat source to sinter powdered material, binding the material together to create a solid structure.

FDM

Fused Deposition Modeling is the traditional 3D printing process that uses a continuous filament of a thermoplastic material. Filament is fed from a large spool through a moving, heated printer extruder head, and is deposited on the growing work.

Feature / Metric	Multi Jet Fusion (MJF)	Selective Laser Sintering (SLS)	Fused Deposition Modeling (FDM)	Firearm Lower Impact
Material Strength	Isotropic: Equal strength in all directions	Anisotropic: Weaker along Z-axis	Highly Anisotropic: Prone to layer splitting	MJF resists cracking better during recoil
Isotropic Mechanical Integrity	Maximum: Identical structural strength along X, Y, and Z axes	Moderate: Z-axis layer bonding is noticeably weaker than X/Y	Low: Weak Z-axis bonds prone to delamination under sudden shear stress	MJF uniformly absorbs multi-directional recoil shock without risk of splitting along flat layer lines
Dimensional Accuracy	High: Finer detail resolution	Moderate: Prone to minor thermal warping	Variable: Highly dependent on printer calibration	MJF ensures drop-in fitment for parts like trigger groups, reinforcement plates, springs, and pins
Surface Finish	Smooth, semi-matte charcoal, then dyed black	Rough, grainy sand-like texture	Visible layer lines and support structure scars	MJF looks closest to a factory injection-molded lower
Porosity & Fluid Resistance	Low: Dense structure blocks gun oils	Moderate: Can absorb solvents if left unsealed	High: Micro-gaps between lines can trap moisture/oil	MJF resists chemical degradation best over long-term use and cleaning
Support Structures	None: Self-supporting powder bed	None: Self-supporting powder bed	Required: Leaves surface blemishes when removed	MJF leaves pristine internal cavities for parts requiring higher, tighter tolerances
Thread & Pin Shear Resistance	High: Fusing agents create a highly cohesive internal matrix	Moderate: Grainy internal structure can micro-fracture under high localized stress	Low: Threaded areas and pin locations easily strip out/ break along extruded filament lines	MJF holds up better to cyclic slap, and grip module pin holes resist egging out under repeated fire
Mating Surface Friction & Fit	Ultra-Low: Smooth, uniform surface reduces mechanical drag	High: Grainy, sandpaper-like texture increases resistance	Variable: Ridged, uneven layer lines create inconsistent drag profiles	MJF provides less resistance in any moving parts such as safeties, safety detents & springs, magazine releases, etc
Environmental & Thermal Stability	High: Uniform material density prevents localized thermal expansion	Moderate: Prone to minor dimensional shifting when exposed to sunlight/heat	Low: Low glass transition temperatures can cause sagging under sunlight/ heat	MJF maintains its exact shape and dimensions during hot rapid-fire sessions or when left inside a hot vehicle

While you can clearly see above why MJF wins over SLS and FDM printing, we also want to dive a little deeper in to the specs of our grip modules in specific. Our grip modules are printed from Nylon12 at a 80.0 µm layer thickness at 100% infill. The Nylon12 is typically grey in color, but is dyed black for our grip modules to better match the OEM HK grip modules. We then post process the grip modules with mechanical finishing to further increase the mechanical and physical properties. The post-processing compresses the surface layer to seal pores, making the component highly resistant to scratches and dirt. It transforms the standard matte finish into a uniform semi/matte-gloss with a softer hand feel compared to unprocessed parts. It also helps to homogenize the outer shell of the part, making it absorb dyes more uniformly compared to SLS or FDM.