LPK Metallurgy

[prepare]

Investment cast, solid bar stock, billet.

Which mil-spec LPK components are solid bar stock and which components are investment cast and why?

To my knowledge the magazine button is aluminum. 6061 or 7075?

Are any components billet?

Keep it technical please.

[prepare]

Listened to this over a couple of commutes. These guys really get into the minutia.
The majority of the larger LPK parts are investment cast. If you really want to get into the weeds on small parts they also discuss pins and springs, types of steel and coatings.
The take-a-way is materials and processes matter. Buying reputable brands is the smart thing to do because there is commercial stuff out there thats doesn't hold up. I recall a widely known brand that had mim bolt catch's in their LPK's that would fall apart.

https://youtu.be/p9uApV0IfbU

[Pappabear]

Prepare, I enjoyed the big shout out to Will Larsen “IraqGunz”. That is one long video that I didn’t have 4 hrs to watch, but jumped around and it had some interesting info.

PB

[prepare]

Gunz was a huge loss that left a big hole here.

[lysander]

Trigger, hammer, safety - precision cast

Magazine catch plate - steel bar stock, or MIM (yep, according to the mil-dwgs)
Bolt catch - precision casting or MIM

Magazine catch shaft, takedown pin, pivot pin, buffer retainer - turned from bar

Magazine catch button, trigger guard - extrusion (7075-T6)

Disconnect - stamped steel

Why? Cost.

Springs - cold formed wire (heat treated after forming)

The following part can also be MIM according to the drawings:
Rear sight base
Rear sight
Front sight post
Ejection port cover latch housing

[m1a_scoutguy]

Here is an all USA-made LPK with NO MIM parts according to the website. Take it for whats it's worth I guess. I have used a few in the last year & while I have not run them hard, torture tested or any other crazy mud/snow/water tests they have performed fine. All installed perfectly in a couple of SOLGW lowers and a few others. So far so good.
https://whitelabelarmory.com/product/ar15-lower-parts-kit-complete/?rs_oid_rd=15474767169472&utm_source=ReSci-Promo+blast&utm_medium=email&utm_campaign=5%252F11%252F2021+LPKs+and+Kits

[Leuthas]

Gunz was a huge loss that left a big hole here.

Wait what?

EDIT*Nevermind. Found it myself. :(

[GH41]

In the end it makes little difference what material or process a part is made from or by if it is done correctly and QC takes a look at it. BCM's claim to fame is inspecting every part. Very few others do. Do you guys really think everyone who sells parts has a contractor who manufactures them exclusively for them?

[lysander]

8620 - trigger, safety, bolt catch, pivot pin, take down pin,

8620 - magazine catch plate (MIM)

4620 or 8620 - hammer

4130, 4140, 4340 - buffer retainer

1065, 1070 - disconnect

1018 - magazine catch plate (bar), magazine catch shaft, detents

303 stainless - trigger guard plunger

One thing I find interesting about the M16/AR design is how 'traditional' it really is, as far as construction methods go. The number of metal stampings is very few, less than half a dozen. And, only five major parts are aluminum.

[prepare]

8620 - trigger, safety, bolt catch, pivot pin, take down pin,

8620 - magazine catch plate (MIM)

4620 or 8620 - hammer

4130, 4140, 4340 - buffer retainer

1065, 1070 - disconnect

1018 - magazine catch plate (bar), magazine catch shaft, detents

303 stainless - trigger guard plunger

One thing I find interesting about the M16/AR design is how 'traditional' it really is, as far as construction methods go. The number of metal stampings is very few, less than half a dozen. And, only five major parts are aluminum.

I wonder if that is due to the designers influence in aviation?

[prepare]

BCM LPK Description-
https://bravocompanyusa.com/bcmgunfighter-ar-15-enhanced-lower-parts-kit-black/

In a commercial market flooded with imported and low quality Mil-Spec imitations, you can trust that BCM® parts are made in the USA and to the highest standards. Please look at the information below.


BCM PNT Trigger Assembly (Polished Nickel Teflon)

BCM quality, modern manufacturing processes, and aerospace coatings are combined to ensure parts last a lifetime while performing far beyond requirements established nearly six decades ago.

The BCM PNT Trigger and PNT Hammer are a precision machined Mil-Spec AISI8620 investment casting per the USGI TDP (Mil-Spec) for M16/M4 family of weapons. (not to be confused with MIM parts that are very common in the commercial market). 156/157 holes are honed to assist in perfect alignment and a smooth trigger pull.

After that, the BCM PNT Trigger and PNT Hammer then goes through a 3 step heat treat and case hardening process for optimal grain structure alignment, yielding a stronger and more wear resistance product..


Polished
The sear engagement surfaces are ground, but then hand polished for an increased smoothness up to 300% beyond the Mil-Spec.


Nickel
An electroless nickel finish is applied for a smoother trigger pull with less grit and reduced felt creep . Nickel also provides a long lasting finish that will not corrode, rust, or discolor due to oxidation.


Teflon
Teflon particles are embedded in the nickel, further reducing the friction of the interface and ensuring a long lasting coating. This is done on both the BCM PNT Trigger and Hammer in order to provide the maximum benefit allowed by the nickel coating, by augmenting the low friction and corrosion resistance.

This assembly includes our impact resistant trigger and hammer pins. They are centerless ground to a fine finish and superior tolerances to ensure compatibility with all MIL SPEC lower receivers built per the USGI TDP.

The BCM Disconnector is stamped from a 1070 material and fine blanked for cleaner edges, double disc ground to precise size. All hammer engagement surfaces are also ground for a super clean reset.

The processes and tolerances are matched in the BCM PNT Trigger Assembly to create a system better than the sum of its parts.


Bolt Catch and Safety Selector

The BCM Bolt Catch and Safety Selector are a Mil-Spec AISI8620 investment casting per the USGI TDP for M16/M4 family of weapons. (not to be confused with MIM parts that are very common in the commercial market)

The Safety Selector is center-less ground. The Selector and Bolt Catch are machined to the Mil-Spec , then goes through a 3 step heat treat and case hardening process for optimal grain structure and wear resistance. Has a phosphate finish for corrosion resistance.


BCM Magazine Catch

The BCM Magazine Catch Assembly (plate and the post) is precision machined Mil-Spec AISI8620 per the USGI TDP for M16/M4 family of weapons. (not to be confused with MIM parts that are very common in the commercial market) and a hardened alloy steel shaft.

The BCM Magazine Catch is machined to the Mil-Spec , then goes through a 3 step heat treat and case hardening process for optimal grain structure and wear resistance. The shaft is hardened, centerless ground, and precision threaded. Parts are assembled and staked per the USGI TDP and given a phosphate finish for corrosion resistance.


BCM Rear Takedown Pin and Front Pivot Pin

BCM Rear Takedown Pins and Front Pivot Pins are made from AISI8620 bar stock and machined per the USGI TDP for M16/M4 family of weapons. Our takedown pins are given a 3 step heat treat processes and the diameters are ground to final size prior to a corrosion resistant phosphate finish.


BCM Detents and Springs

Takedown detents include a cadmium chromate coating to resist corrosion and prevent them seizing in the small holes of the lower receiver while the Buffer retainer and Bolt Stop Plunger are made from hardened alloy steel for wear resistance and finished with a phosphate coating to prevent corrosion. The Springs are 17-7PH Stainless Steel to prevent corrosion and retain adequate tension for a lifetime of service.

[Five_Point_Five_Six]

I've used the BCM parts kits on a few lowers now and they're consistently good. You get a quality LPK, the mod 3 grip which is my favorite grip, and a trigger that is cleaner and smoother right out of the package than a standard GI trigger. I certainly wouldn't pay $70 for a PNT trigger separately, but the LPK with grip and trigger is a bargain at $120.

[AndyLate]

I've used the BCM parts kits on a few lowers now and they're consistently good. You get a quality LPK, the mod 3 grip which is my favorite grip, and a trigger that is cleaner and smoother right out of the package than a standard GI trigger. I certainly wouldn't pay $70 for a PNT trigger separately, but the LPK with grip and trigger is a bargain at $120.

I absolutely second this!

Andy

[Spooky1]

I absolutely second this!

Andy

+ 1 more 😁

[Sparky5019]

The BCM LPKs are first rate. I’m all BCM when I can be but I’ve also had zero issues with the CMMG LPKs without FCG. They perform as well and are decently priced. That’s my only issue with having to buy BCM complete LRGs. Lol. I end up with a bag of shit I don’t need. Lol. I’m glad they’re offering the stripped SX4 lowers in a limited way; gives options.

[pag23]

The only LPKs I could get recently were CMMG and SOLGW.....that being said my triggers are mainly SSAs and MBTs..the only BCM PNT I have will be replaced by an SSA if there is a decent Memorial or Black Friday sale