Extractor Steels

[Straight Shooter]

Been researching bolt/bcg's info for awhile now.
Ive noticed a number of different steels being used for extractors. Examples are: D2 & S7 Tool Steel, 4340,4140..and Im sure many others.
What are considered to be the best materials for an extractor? And why would a certain one not be a good choice?
If you were building a bolt...money be damned...what would YOU use & why?
Thanks for any info.

[lysander]

4140 or 4340 properly hardened to 42 to 44 RHc which gives about 170,000 psi yield strength.

These steels give a good balance between strength, toughness, hardness, machinability and cost,

Because in my world money is never to be damned.

[Nocalsocal]

At what point do we sacrifice hardness for durability. I've also noticed all the different steels these past few years and wondered why?
Where or what is the perfect nexus between hard vs brittle for all these steels in the bcg?

Sent from my SM-G935V using Tapatalk

[26 Inf]

Doesn't the mil-spec allow for 4140 or 4340?

A brief look, at Google (I'm not an engineer) revealed:

AISI Machinability Rating: 4130 = 70%; 4340 = 50%

Annealed Tensile Strength: 4130 = 81,300 psi; 4340 = 108,000 psi

Yield Strength: 4130 = 52,300 psi; 4340 = 68,500

Brinell Hardness: 4130 = 156; 4340 = 217

Seems to me the .gov thought 4130 was 'good enough. '

Several manufacturers obviously think that 4340 offer enough advantage that it is worth the additional tool wear and raw material cost.

[lysander]

Doesn't the mil-spec allow for 4140 or 4340?

A brief look, at Google (I'm not an engineer) revealed:

AISI Machinability Rating: 4130 = 70%; 4340 = 50%

Annealed Tensile Strength: 4130 = 81,300 psi; 4340 = 108,000 psi

Yield Strength: 4130 = 52,300 psi; 4340 = 68,500

Brinell Hardness: 4130 = 156; 4340 = 217

Seems to me the .gov thought 4130 was 'good enough. '

Several manufacturers obviously think that 4340 offer enough advantage that it is worth the additional tool wear and raw material cost.

The strengths you have quoted are the annealed strengths. You will find the strength of these two steels when hardened to 42 to 44 RHc are pretty much the same - around 150,000 psi. They are both more than adequate for the job.

[Straight Shooter]

Whats yalls opinion on the Tool Steels...D2 & S7?

[26 Inf]

The strengths you have quoted are the annealed strengths. You will find the strength of these two steels when hardened to 42 to 44 RHc are pretty much the same - around 150,000 psi. They are both more than adequate for the job.

I was researching different stuff based on a premium BCG description:

Bolt: precision machined from Carpenter Technology No. 158 gun quality aerospace alloy, heat treated per mil-spec (stress relieve, carburize, oil quench, temper, refrigerate, repeat temper), shot peened per ASTM B851/SAE AMS2430S, vibratory tumbled, individual high pressure/proof test fired, individual magnetic particle inspection ASTM E1444/E1444M, ultrasonically cleaned, markings deep laser engraved (SP=Shot Peened/HPT=High Pressure Tested, MPI=Magnetic Particle Inspection/158U=Car Tech 158 alloy type and Umbrella manufacture), manganese phosphate

Extractor: precision machined from 4340 tool steel alloy per SAE AMS6415T/AMS6484D (vs typical 4140; mil-spec allows for either 4140 or 4340), heat treat, shot peen per ASTM B851/SAE AMS2430S, markings deep laser engraved (SP=Shot Peened/4340U=alloy type & Umbrella manufacture), manganese phosphate

Extractor Retaining Pin: precision machined and ground S2 shock resistant tool steel alloy per ASTM A681-08 (vs typical S7; mil-spec allows S1 to S7), heat treated per ASTM A681-08, shot peened per mil-spec print, manganese phosphate

Extractor Spring: (premium spring eliminates need for Crane O-Ring), Tactical Springs/Sprinco 5 coil, ASTM Grade A401 Chrome Silicon wire stock, heat treated, stress relieved, Molybdenum-Disulfide infused, cryogenic processed (all post winding), mil-spec black insert/synthetic elastomer extractor buffer (nitrile-butadiene, shore hardness 80+/-5 durometer per MIL-PRF-6855)

Ejector: S2 shock resistant tool steel alloy per ASTM A681-08 (vs typical S7; mil-spec allows S1 to S7), heat treated per ASTM A681-08, shot peened per mil-spec print, manganese phosphate

Ejector Spring: Tactical Springs/Sprinco ASTM Grade A401 Chrome Silicon wire stock, heat treated, stress relieved, Molybdenum-Disulfide infused, cryogenic processed (all post winding)

Gas Rings: mil standard stainless steel X3

Carrier: machined from AISI 8620 aircraft qualty alloy per ASTM A108/A322-13, full auto profile, surface finish improved over mil-spec, heat treated (carburized/strain relieved per mil-spec print), hard chrome bore, precision ground gas key interface, Umbrella logo deep laser engraved, manganese phosphate

Gas Key: machined from 4130 chromoly steel alloy per ASTM A108/A322-13, heat treated, hard chrome internal, manganese phosphate, Permatex sealed, Grade 8 Torx Plus cap screws torqued and staked all per mil-spec

Cam Pin: precision machined 4340 chromoly steel alloy per SAE AMS6415T/AMS6484D, heat treated/processed per mil-spec, manganese phosphate, solid film lubricant applied and cured per mil-spec

Firing Pin: precision machined 8640 steel alloy, heat treated/processed per mil-spec, hard chrome plate

Firing Pin Retaining Pin: 1038 carbon steel, heat treated/processed per mil-spec, manganese phosphate

All components, material, and packaging made in the USA

I guess my questions are

1) isn't all machining somewhat precision?

2) does the upgrade from the base mil-spec materials to the upper end mil-spec materials significantly impact reliability and longevity?

[17K]

I don't know what Colt uses, but I've had great service out of theirs, 16" carbines with all 5.56 ammo, much MK262.

Their extractors that come with the spring and insert are what I use to fix/replace extractors with.

[lysander]

I was researching different stuff based on a premium BCG description:

STUFF

I guess my questions are

1) isn't all machining somewhat precision?

2) does the upgrade from the base mil-spec materials to the upper end mil-spec materials significantly impact reliability and longevity?

1) Depends on the the drawing. If you specify on the drawing +/- .100", that not very precise at all, if you specify on the drawing +/-.0001", that really precise.

2) There is no such thing as a "better" material. You will always have a trade-off in cost, producability, toughness, strength, weight, fatigue properties, nature of failure (does it snap like glass, or stretch like silly-putty), etc, etc. Materials are chosen for the best balance of all of these properties, and their intended use. If you change the point of balance, say you're going to accept higher production cost, then yes, you can get improvements in other areas. The question then becomes (for the consumer): "Is it worth it?"

How often do you see a properly made (mil-spec) extractor fail? How long does a properly made extractor last under normal, or even rough conditions?

When the Army did a study to baseline the reliability of the M16/M4, they found these parts do not fail all that much in service, (and the Army can't tell if the extractor is made from 4340 of 4140, so for all practical purposes they are the same). So, to me the increase cost of a "better" extractor isn't worth it. If you want an vibranium or adamantium extractor and have the deep pockets required, it might be worth it to you.

[26 Inf]

Lysander - Kind of what I thought. Thanks.