Hammer/Trigger Pin Reviews
If you haven’t already done so, we recommend that you read the Hammer and Trigger Pins article in our design section to familiarize yourself with the options and benefits of each type.
Continue reading below for a detailed overview of what we look for in hammer/trigger pins.
Standard Pins
Anti-Walk Pins
Review Considerations
Price and Value
Hammer/Trigger Pin Material
The core material of a component determines the principal properties of that component.
Different metals are suited for different things based on their physical and mechanical properties. For hammer/trigger pins, there are unique stresses that are encountered by the metal. Choosing a material should account for these stresses.
Density: The weight of the material for a given volume.
The lower the density of the material used to create the hammer/trigger pins, the lower the weight. While weight is an important consideration for a battle gun, these pins are some of the smallest components, and the difference in weight between materials is not particularly significant.
Hardness: Resistance to localized plastic (i.e. permanent) deformation, such as scratch or indentation induced mechanically.
As these pins are subject to the hammer and trigger rotating over them, we want harder pins over softer pins.
Tensile Strength (Ultimate): The maximum stress a material can withstand while being stretched or elongated before breaking.
UTS is less important for the hammer/trigger pins because we do not stretch them. However, this measure is often used to describe the general strength of a material.
Tensile Strength (Yield): The limit of the elastic behavior (bounces back to original shape/length after deformation) and transition to plastic behavior (does NOT bound back after deformation) of a material when stretched.
As with ultimate tensile strength, this measure is more of a general property of the material and doesn’t directly translate to the hammer/trigger pin stresses.
Young’s Modulus: This measure tells us how much a material can be deformed before it transitions from elastic deformation (it will return to the original length/shape) and plastic deformation (it will NOT return to the original length/shape).
This is effectively a measure of stiffness/rigidity. In the context of hammer/trigger pins, rigidity is a good thing. Rigid means precise alignment and efficient transfer of energy.
Shear Strength: The amount of shear stress that can be applied before failure.
This is a relevant measure for hammer/trigger pins. Hammer pins, in particular, experience significant moments of shear stress as the hammer falls, strikes the BCG, and is pushed back into position as the BCG rides rearward.
Elongation at Break: This is the amount that the material will stretch, relative to the original length, before it breaks.
This is a measure of ductility, which is the inverse of brittleness. The more a material stretches before it breaks, the higher this number will be, implying that it is more ductile and the less brittle.
Reduction of Area: This is the relative change of cross-sectional area of a material relative to the original cross-sectional area, when stretched to breaking.
As with elongation at break, this is a measure of ductility/brittleness. The more a material stretches before it breaks, the higher the reduction of area will be, implying that it is more ductile and less brittle.
The table below compares these measures between 4140 steel, 304 stainless steel, and Grade 5 titanium.
Selecting a material for hammer/trigger pins is a balancing act. As a reminder, we want a hard, rigid, ductile, and shear-resistant metal. You won’t find the best of everything in any one material.
Stainless steel is the most ductile of these metals, but its also the softest (by a lot).
Steel is the stiffest and strongest of the three metals and has excellent ductility and hardness, but has the lowest shear strength.
Titanium is the lightest and hardest of the three metals and has an incredible strength-to-weight ratio and amazing shear strength, but it is also the most brittle and least stiff.
Hammer/Trigger Pin Finish
Generally, bare metal is not desired for any parts that experience mechanical abrasion, especially if the base metal does not have exceptional hardness and corrosion resistance.
The finish of a component influences the appearance, corrosion resistance, and resistance to wear.
The finish can impart surface characteristics that differ from the base material. For example, stainless steel is very soft and therefore susceptible to localized deformation (scratching, denting, etc.). A nitride finished stainless steel, on the other hand, has good surface hardness while maintaining a ductile core.
The standard Mil-Spec finish for hammer/trigger pins is manganese phosphate. Manganese phosphate increases the surface hardness and lubricity of a metal through the adhesion of manganese phosphate to the surface of the metal.
Another finish that can be found in hammer/trigger pins is nitride. The nitride finish is applied by diffusing nitrogen into the surface of the metal, resulting in a case-hardened surface. A nitride finish is a step up from manganese phosphate, offering additional hardness and lubricity.
Another finish that can be found in hammer/trigger pins is diamond like carbon (DLC). DLC has exceptional hardness and lubricity. However, it must be applied properly to ensure adhesion. Because it is so hard (often much harder than the core metal), it can flake off if not properly bonded to the substrate (think of a chocolate-covered strawberry). When done right, DLC is superior to every other finish that you’ll find on an AR.
Hammer/Trigger Pin Length
Hammer/trigger pins need to be long enough to span the trigger pocket in the lower receiver and be adequately supported by the walls of the lower receiver.
Hammer/trigger pins also need to be short enough that they aren’t protruding excessively from the sides of the receiver. Excessive length can be a nuisance for anti-walk pins, in particular; if the shaft is too long, the pins may float from side to side.
We have taken measurements of a couple different receivers for reference:
Based on these measurements, we want to see the following:
Target Length (Standard Only): 22.38-22.60mm
Maximum Length (AWS Only): 22.45mm
1: We do NOT recommend anti-walk pins on the EPC platform. The lower receiver is narrower than the AR-15/M4E1 and AR-10/M5 receivers. AWPs on this platform will slide from side to side due to the excessive length. Out of all the AWPs that we tested, only one of the two Armaspec pins fit without lateral motion (the second one was too long for the EPC lower).
Hammer/Trigger Pin Diameter
The Mil-Spec diameter of the hammer and trigger pin holes in the lower receiver is 0.154 inches (3.91mm).
For standard hammer/trigger pins, the minimum diameter we want to see is 0.1540 inches. This ensures a tight fit and minimal perceived wiggle and slop in more refined 2-piece trigger systems.
The diameter of AWPs is a little less important than for standard pins when coupled with drop-in triggers. For AWPs we want to see a minimum diameter of 0.1535 inches.
New lower receivers will generally have tighter pin holes than worn receivers. For new receivers, we are looking for a maximum diameter of 0.1545. Anything larger than 0.1545 and you will struggle to install the pin without whacking the holy hell out of it or reaming out the pin holes (DO NOT EVER DO THIS).
Some standard pins are designed for worn receivers and will intentionally have larger diameters between 0.1550 and 0.1555 inches. We do NOT recommend that you try to cram these into a new receiver.
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