TECHNICAL TEST & EVALUATION DATA
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CP-R360 CAM PIN
Receiver & Cam Pin Design:
Cam Pin wear in AR patterned weapons has been well observed.
The cam pin interacts with the upper receiver as the bolt reciprocates in both directions. As the BCG (Bolt Carrier Group) travels forward the bolt strips a new round from the magazine and this action causes the cam pin to rotate very slightly within the upper, it is forced against the left hand side wall of the guide channel. As the round leaves the magazine and enters the chamber resistance is reduced.
As the bolt goes into battery the lugs engage with the extension and stop any further rotation of the cam pin until the parts are fully engaged, at which point the cam pin rotates and comes to rest within the cam pin recess. The action of stripping a round is predominantly power by spring energy, however, over gassed systems can suffer from buffer bounce and the increase in carrier velocity and energy (aided by the action spring) as the parts travel forwards.
In any event the first point of forward travel rotational impact from the cam pin is further back within the channel, as compared to the leading edge of the campin recess.
It is the process of firing and the resultant introduction of high velocity carrier movement that causes the most wear. This can be observed in both Direct Impingement and Piston driven systems.
The rectangular shape of a standard cam pin exacerbates the situation as the geometry is not sympathetic to the internal surfaces of the receiver.
Armalite had identified this problem in the 1950's when Eugene Stoner was developing his AR10 belt fed system. Clearly the higher round count and faster BCG velocity was causing issues and to combat that they manufactured a Roller Cam Pin solution, this ultimately did not see mainstream production due to lifespan issues as the support for the roller added another point of failure to the system.
Obviously reducing friction reduces wear and increases lifespan
After firing gas enters the carrier via the gas tube and inpinges against the gas rings, it forces the carrier rearwards while also forcing the bolt forwards until the gas rings pass the secondary carrier ports where gas vents and pressure equalises. As the carrier moves rearwards the bolt is forced to rotate as the cam pin travels through the carriers cam pin channel. Its this 'expansion' effect that produces less wear in a DI (Direct Inpingment) weapon vs a Piston driven system, its also the reason that springs are used on the tails of piston driven bolts as they assist in unlocking and thus reduce wear.
As the bolt unlocks from the barrel extension it does not complete a full rotation back to its vertical position. It stops rotating at the exact point the bolt and extension lugs clear each other (remember there are tolerances between the two dimensions) and this creates a situation where the cam pin is still slightly canted over as it moves backwards. It is at this point the cam pin strikes the leading edge of the cam pin recess and causes a notch to form.
A number of manufacturers have fitted steel inserts into the cam pin recess leading edge, this adds complexity and weigth and would appear to simply move the point of wear to another location.
Design: Steel Insert relocates wear position.
This extended steel wear insert would appear to have simply relocated the point of interaction between the upper receiver and the cam pin to the point where the stronger material meets the weaker. The key to understaning this interaction is BCG velocity.
Cam Pin surface smoothness comparison:
Surface roughness measuring was conducted using Mitutoyo SJ-210 calibrated tester.
Comparison: Lantac Smoothcam vs Standard & Enhanced variants.
Image A, Lantacs ultra smooth CP-R360 cam pin features a surface smoothness of 2.01 Ra (Roughness Average).
Image B, a standard Phospate (TypeM) milspec cam pin measures 30.31 Ra.
Image C, an enhanced NiB (Nickle Boron) coated cam pin measures 20.42 Ra.
CP-R360 Smoothcam Cam Pin Durability.
After 75,000 rounds of test firing the cam pin was submitted for 3rd party testing, both MPI (Magnetic Particle Inspection) & Radiography testing was undertaken.
Durability: Third party testing confirms cam pin integrity.
MPI testing detected no cracks which was also confirmed by X-Ray analasis. The lab report details that no damage indicators could be found. The cam pin exibits normal wear conditions from interaction with the bolt and remeains perfectly servicable.
Durability: 75,000 Round surface smoothness.
The CP-R360 cam pin remains smooth at 5.14 Ra. It is still considerably smoother than standard & coated parts tested.
Durability: Internal Wear Resistance Comparison.
Image A, Standard rectangular cam pin wear after 1500 rounds, a sharp wedge cut has started to form at the leading edge of the cam pin recess..
Image B, Another view of 1500 rounds of wear from a standard rectangular cam pin. The erosion of material by the pins head causes an increase in friction to the working parts and adds unnecessary stress.
Image C, illustrates 75,000 rounds of wear from a Lantac CP-R360 Cam Pin. A small section of leading edge has been worn but the recess is not deep and remans localised to the edge only.
Friction is reduced and the working parts are under less stress.
Image D, Extreme cam pin wear to the point of failure. An extended deep groove has been formed over 100,000+ rounds in this rental range gun.