E-BCG DESIGN DEVELOPMENT & TESTING
E-BCG Design:
One of the most significant evolutions Lantac-USA LLC has brought to market has been its E-BCG (Enhanced Bolt Carrier Group) for M16, M4, AR15 Patterned rifles.
Standard mil-spec BCG’s vent gas at 90 degrees to the bore with an un-shrouded porting system. With the ever-increasing use of short barreled rifles (SBR’s) and suppressors on AR platforms, propellent gasses escaping from standard BCG's tend to interact negatively with the operator as well as increase carrier velocity that places extra stress loading to the working parts. Lantac has solved gas flow and reduced gas/ operator interaction by giving the two main venting ports a forward-facing gas trajectory and then angling, shrouding and enlarging the primary gas port to allow expanding gasses an avenue forward and out of the ejection port instead of flowing into the back of the upper receiver and into the shooters face through the charging handle slot.
The BCG’s carrier is precision machined from military specification 8620 steel and all critical diameters are hard ground after heat treatment (for maximum accuracy and precision), as per the military standard.
Heat treatment imparts a 89.5 to 91 Rockwell 15N case hardness to the part.
Bolts are precision turned from billet Carpenter 158 steel, again in line with the military specification. They are hard ground after heat treatment, heat treatment imparts an 89-90.5 Rockwell 15N case hardness, in addition bolts are S110 shot peened for strength and MPI (Magnetic Particle Inspected) tested, a process that identifies surface cracking and weakness, prior to installation.
Firing pin channel diameter and pin protrusion are also checked.
Firing pins are precision turned from 8740 steel with a 45-49 HRC Rockwell hardness, they are hard chrome plated to MIL-STD-171 1.2.2.4.
The enlarged and forward-facing gas ports allow more gas to exit the carrier rather than over pressurize it like a standard design. The acceleration of the Lantac E-BCG carrier is thus slower with a softer start to reciprocation, less stress is applied to the bolt lugs and cam pin, cycle speed is reduced as is recoil energy.
Standard designs accelerate the carrier extremely quickly causing the bolt to be ‘snatched’ out of battery which causes increased loading on the lugs / cam pin and induces fatigue stress.
A Photron SA-X Fastcam was used to analyze BCG behavior in the following images that were filmed at 20,000 frames per second.
Design: The Standard Carrier.
Gas escapes at 90 degrees to the bore in a standard carrier, as the carrier reciprocates backwards this gas is forced against the interior wall of the receiver and eventually into the operators face through the charging handle slot.
The smaller port hole diameter allow more gas to escape around the firing pin rearwards. The rear section of the weapon system receives additional fouling and this situation is worsened through the use of suppressors that increase back pressure. Fouling enters the buffer tube and accumulates on the trigger group.
Design: Lantac E-BCG.
The forward-facing enlarged ports handle gas flow in a more efficient manner that reduces the level of potential hazardous fumes the operator is subjected to.
Gas is directed forwards away from the users face and diffused to the atmosphere.
Back pressure from suppressors is reduced too (not eliminated) as well as the resultant fouling that over pressure causes.
Design: Lantac E-BCG.
In this example excess lubricant has been used to demonstrate how the E-BCG directs gas forwards away from the operator.
Design: Lantac E-BCG.
This UK MOD Special Forces L119A2 Assault Rifle running a Surefire SOCOM556 suppressor has been fitted with an E-BCG that clearly illustrates how fouling is localized to the front surface of the BCG, the bolt and extension lugs do not receive additional fouling as propellant gas is ejected out of the port, away from these parts. The horizontal cut below the 'LANTAC' logo gives gas an escape path out of the upper receiver as the carrier moves backwards.
Design: The Extended Cam Track argument.
A number of other manufacturers produce bolt carrier groups with extended cam tracks that many consider to be a superior design using the concept that the extended track increases 'lock time' of the bolt within the barrel extension and is intended to reduce cyclic rate and increase dwell time. The carrier can theoretically move backwards a short distance before engaging the cam pin and starting the bolt unlocking process, therefore the bolt remains locked up for longer and the cyclic rate is reduced.
Unfortunately, the opposite is actually true.
The extended track allows the carrier to accelerate faster than normal as there is no interaction with the cam pin (that actually slows acceleration) at the same point as a standard BCG. The carrier is allowed to accelerate without hindrance, this faster than normal carrier movement applies increased stress to the cam pin and bolt lugs as it forces these parts out of battery.
Brass is ejected faster than normal and the higher velocity increases recoil and BCG cyclic rate.
Design: The Extended Cam Track E-BCG.
This diagram illustrates the difference in length
of an extended cam pin track vs a standard track (at bottom), this is a prototype E-BCG developed to test the theory.
Design: Testing Extended Cam Track BCG's against the original E-BCG.
Filming at 5000 Frames Per Second three Extended Cam Track BCG's (A,C & D) were tested against the E-BCG (B) . BCG (C) was the Lantac prototype Extended Cam Track E-BCG.
The same weapon system and ammunition (Black Hills 70Gr Barnes TSX Optimized) was used throughout the experiment.
High speed testing clearly indicates that extended cam track carriers out accelerate, eject brass and cycle faster than standard track carriers.
Note: Other manufacturers logos are blurred for privacy.
In addition full auto shot timer testing (using a professional PACT XP Mk IV timer) was conducted to establish a 30Rnd cyclic comparison.
A 14.5'' Mid-Length gassed rifle firing 62g SS109 was used for the test.
BCG (A) produced a 30Rnd shot string in: 1.850 seconds.
Lantac E-BCG (B) produced a 30Rnd shot string in: 2.141 seconds.
BCG (C) produced a 30Rnd shot string in: 1.966 seconds. The enlarged ports of the E-BCG still having an effect on reducing acceleration.
BCG (D) produced a 30Rnd shot string in: 1.796 seconds.
Conclusion: The extended cam track concept was rejected as having no benefit in an enhanced system.
Design: Number of ports, size & position.
Standard carriers have two ports positioned in such a way that as the bolts gas rings swipe past them pressurized gas is allowed to vent to atmosphere. The number of ports, their position and diameter have a marked effect on how gas escapes the carrier.
As can be seen in the above stills the E-BCG (A) directs gas forwards with the primary port actually blowing gas over the two secondary ports, this creates faster mixing with air and diffusion of the gasses. The standard carrier (B) produces two traditional 90 degree plumes while a three port carrier (C) produces a much larger gas cloud also at 90 degrees to the carrier.
Both carriers (B) & (C) produce visibly more gas than the E-BCG (A).
These images were taken at exactly the same time in the firing cycle using the same ammunition in the same weapon system.
Design: Advanced Hydraulic Staking.
Gas keys are installed with ‘milspec’ Permatex aviation gasket sealant (Part No 80019) and retained by improved grade 8 screws.
After torquing to the standard military specification of 50-58 inch/pounds advanced hydraulic
staking is utilized that creates an improved flow of metal around the screws knurled head and breaking torque is increased to 132 inch/pounds over the mil specification of 55-100 inch/pounds. A further improvement in reliability.
Design: CPR-360 Domed Head Cam Pin.
The patented CPR-360 dome head cam pin is machined from 17-4 PH (Precipitation Hardened) stainless steel and then heat treated to an H900 condition, it is extremely tough and hard wearing. The domed head is precision swiss machined with an ultra-smooth surface that is then polished to a 2-3 Ra. The pin has a circular profile with a domed head that presents completely different geometry to the inside of the upper receiver, friction and wear are reduced and performance is increased.
Design: CPR-360 Domed Head Cam Pin.
Using a calibrated Mitutoyo SJ-210 surface roughness tester the CPR-360 Cam Pin head was tested for smoothness against a number of competing products.
The resultant measurement from a new CPR-360 cam pin is 2.01 Ra (Roughness Average), (approx) 1.23 RMS, (Root Mean Square).
The resultant measurement from a standard phosphate cam pin is 30.31 Ra (Roughness Average), (approx) 33.64 RMS, (Root Mean Square).
The resultant measurement from a Chrome plated cam pin is 20.42 Ra (Roughness Average), (approx) 22.66 RMS, (Root Mean Square).
Design: Increasing Accuracy.
The Lantac E-BCG features a patented flared tail to the rear of the carrier, this feature increases the concentricity of the carrier within the upper receiver, which in turn aids in increasing accuracy as the position of the bolt remains more consistent in relation to the chamber.
There is also less carrier tilt at the time of firing. Carrier tilt is normally encountered in piston driven systems when the operating rod strikes the anvil of the carrier and drives it backwards, in this scenario the tail of the carrier is driven downwards and increased wear to the tail of the BCG and buffer tube mouth can be evidenced.
A similar effect can be felt when gas pressurizes a standard carrier, the flared tail of the E-BCG stops excessive carrier movement and delivers a much flatter reciprocating action that is quite noticeable.
Design: Accuracy & Concentricity.
The improved concentricity of the carrier inside the upper receiver also combats another relatively unknown phenomenon which is pressure exerted on the carrier from ammunition in the magazine.
As rounds are fed by the follower they stack biased either to the left or the right of the feed lips and with a full magazine the pressure exerted on the standard carrier moves it slightly in battery, so much so that individual shot groupings can be observed to move under careful examination.
This effect is diminished when tested with an E-BCG Bolt Carrier Group.
Evidence: Proof Research.
Design: Accuracy Testing.
A well known brand AR15 rifle was used for test firing which was conducted with the standard carrier supplied and then with a Lantac E-BCG. The rifle came fitted with a 5.56x45mm chambered 10.3’’ 1:7 twist cold hammer forged barrel and A2 compensator. Ammunition used was the Black Hills 70Gr Optimized Barnes TSX and shot at 100 yards range. This was a man fired, bench rest test.
Design: Accuracy Testing.
Left:
A 5-round group of 3.01’’ (2.88 MOA) was achieved from the standard carrier.
Right:
After the Lantac E-BCG was fitted the 5 round group size shrank to 2.27’’ (2.16 MOA).
A .740’’ improvement.
Applied Ballistics analysis gives a hit rate probability of 90.2% at 656 yards (600m) with the E-BCG as compared to the standard rifles carrier hit rate of 81.4%.
Design: Recoil Testing.
Testing was undertaken to measure the E-BCG’s ability to reduce recoil energy. The test was conducted against a standard ‘MILSPEC’ BCG. Ammunition used was Black Hills 70Gr Barnes TSX Optimized., running in a 10.3’’ barrel upper receiver group with carbine length gas and A2 Flash Hider.
The URG (Upper Receiver Group) was shot with the standard BCG and then the Lantac E-BCG.
The URG was shot with a standard carbine 3.0oz buffer and spring.
The URG was held in a Bill Wiseman test sled and a PCB Electronics 4010 L-CELL Load Cell was mounted to the test jig so that it was in contact with the sled at the time of firing. Recoil loading was then measured under firing to establish if a difference could be measured.
Data was captured with a Crystal Instruments CoCo-80X Dynamic Signal Analyzer.
Design: Recoil Testing.
Firing of the system was undertaken remotely so that operator interaction could not influence results.
Design: Recoil Testing.
Standard BCG: 3 shot average generated 2.527 LBF (Pounds of Force).
Lantac E-BCG: 3 shot average generated 2.466 LBF (Pounds of Force).
There was a 2.41% Reduction in recoil LBF (Pounds of Force) between the standard BCG and the Lantac E-BCG.
Design: Conclusion.
The 5000FPS high speed video above demonstrates the cyclic speed difference between the Lantac E-BCG, a MILSPEC standard BCG and an extended cam track carrier BCG.
The Lantac E-BCG reduces cycle time, reduces recoil, reduces wear, increases accuracy and produces less potential harmful gas exposure to the operator than the other BCG's tested.
Note: Other manufacturers logos are blurred for privacy (center of video).
E-BCG Durability.
Multiple US military reports have investigated MILSPEC bolt failure in M16 & M4 weapon systems. A 2004 USMA report on bolt failure of the M16 Rifle details how crack initiation would begin at the rear of the lugs usually adjacent to the extractor, either lug could fail. After forming the crack would propagate forwards towards the bolt face along the recess surface between the lugs.
Durability: Crack Initiation.
Note the crack initiating from the rear of the lower lug that travels forward in an arc across the surface between the lugs.
Formation of the crack was assessed as being due to wear of the protective phosphate coating that exposed base metal to corrosion & pitting after only 1800 rounds. A hardness test also revealed that the base of the lug was 100 units softer than the surrounding material. After 3600 rounds a notch was observed to form that may result in a stress riser which facilitated crack propagation and deeper corrosion penetration, the weaker case hardness also allowing the crack to initiate in this location.
Lug stress under firing, surface hardness and coating quality are therefore essential requirements for increased bolt lug lifespan.
Image Credit: USMA.
Durability: Propagation to failure.
The above image details complete failure of an M16 bolt, which is even more common in the shorter barreled/ gas system M4A1 Carbine.
Crane NAVSEA's 2015 report details a 12,600 round endurance test of the M4A1 10.3’’ RIS II Upper Receiver Group. Page 16 of the report covers bolt lug breakage across the trials. Bolt lugs failed in the same location as the USMA 2004 report with an average bolt lifespan of only 9625 rounds! The best achieved round count was 11,881 and the worst 7,890.
Image Credit: USMA.
Durability: Lantac 75,000+ round count E-BCG.
Lantac has supplied rifle systems to rental ranges across the USA and a well documented round count rifle was returned for durability analysis. The report detailed in excess of 75,000 rounds of full auto mainly suppressed fire. The E-BCG was disassembled and the Carpenter 158 bolt and CP-R360 cam pin were sent out for third party MPI testing.
Durability: Third party MPI testing.
NDE Labs Inc. MPI testing establishes the initiation of two micro cracks in the suspected locations, crack propagation was however extremely limited.
The CP-R260 domed head cam pin remains un affected.
Durability: Microscope analysis.
Residual MPI (Magnetic Particle Inspection) die reveals the initiation of two micro cracks on both lugs adjacent to the extractor area. Viewed through a microscope these cracks do not penetrate past the coating and the integrity of the bolt remains unaffected.
Durability: Third party Radiography testing confirms bolt integrity.
Testing conclusions indicate that the E-BCG bolt is still in a perfectly serviceable condition; while cracking has initiated, it is limited to the surface of the alloy (only in the coating surface) and has not penetrated into the substrate at this stage.
The Lantac E-BCG’s bolt has sustained an extremely high round count of full auto fire that was well above any attainable level the Crane test weapons could achieve.
Durability: Third party corrosion resistance testing.
G2MT Laboratories. Lantac's specification NiB (Electroless Nickel Boron) applied to AMS2433B and Nitride QPQ (Quench Polish Quench) applied to AMS2753B standards. Coatings pass and exceed US MIL-STD-810 and DEF STAN 00-35 Salt Fog corrosion resistance testing.
Durability: Controlled Salt Fog endurance testing, 72 hours.
Both the Nitride QPQ and NiB BCG's have sustained limited corrosion damage as compared to the Phosphate (Type M) control carrier (pictured at center). This test clearly demonstrates the improvements made to BCG longevity by utilizing advanced coatings applied to the correct standards.
E-BCG Conclusions.
The Lantac E-BCG (Enhanced Bolt Carrier Group) stands out as an exceptional choice when compared to standard BCGs. Its innovative design, precision machining, and enhanced features such as reduced felt recoil, improved cycling reliability, and easy cleaning make it an exceptional option for firearm enthusiasts and professionals alike. The Lantac E-BCG represents a significant advancement in terms of performance and functionality, making it a valuable upgrade for those seeking the utmost in reliability and shooting experience.