A different type of metal for manufacturing bolts for bolt carrier groups?

[Dennis]

I would guess that an in spec C158 or even 9310 bolt has the advantage of seeing billions of rounds downrange with a known working profile. Knowing what to expect to work around it, like replacing a bolt every 8K rounds or whatever, is more "reliable" than one made out of ubontanium with only a history of thousands of rounds.

I just keep a spare bolt in all my grips, virtually guaranteeing no bolt issues

Dennis.



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[shadowspirit]

I would guess that an in spec C158 or even 9310 bolt has the advantage of seeing billions of rounds downrange with a known working profile. Knowing what to expect to work around it, like replacing a bolt every 8K rounds or whatever, is more "reliable" than one made out of ubontanium with only a history of thousands of rounds.

I just keep a spare bolt in all my grips, virtually guaranteeing no bolt issues

Dennis.



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I thought people that keep a spare in their grip typically have the whole bolt carrier group.

[Dennis]

I tried but a whole BCG wouldn't fit in my grip...

I keep spare tested BCGs in my bag as well as consumable parts. Again guaranteeing that whatever breaks won't be whatever I have with me!

Dennis.



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[lysander]

I don't know how much stronger 4340 is compared to Carpenter 158 and 9310 is but if it is much stronger it would probably be worth it for the gucci brands to use because that's another thing to advertise their claims of building superior rifles. Ditto for the exotic metals. If a gucci brand advertises it costs more and is difficult to machine, that would appeal to AR enthusiasts who have money to buy the best stuff, I guess. I'm not sure as I'm not on the level of buying a $2500 or $3000 AR. I don't know how many are attracted to and buy the $3000 ARs out there. I know there are many that like and buy the $3000 1911 pistols.

While 4340 can be hardened to a yield strength of 220,000 psi (9310 and 158 in bolts runs around 135,000 psi at the core), with a hardness of RHc 44, it is not considered a good candidate for carburizing, so you are stuck with through hardening which won't give a hard surface, or induction hardening which is not appropriate to the geometry of an AR bolt.

The M2 and M85 bolts have huge bearing surfaces so a super hard surface (RHc 58-60) is not critical, the M2 bolt is only the equivalent of RHc 50.

[lysander]

I wouldn't have guessed that. IIRC, a Russian submarine was made of titanium.

Submarines are not bolts.

Ketchup is great on hamburgers, but terrible on ice cream. Just because something works well in one application, does not mean it is good in a different one.

[Slater]

Regarding 4340, the Turkish BRG-9 Elite handgun is advertised as having the barrel and slide made from this grade of steel. Don't know if they're unique in this or if there are other handguns with similar specs.

"They then subject the slide and barrel to a double heat-*treatment process. That is done to produce a harder surface while maintaining a tough core or interior, which keeps hard parts from being perhaps a bit brittle. In effect, you get the surface hardness of a 4350, and they get the machinability of the 4340 alloy. This is not a new idea, it has been done for over a century in manufacturing, but it does take extra time, steps and equipment, so hats off to Burgu for going those extra steps for our benefit."

https://www.firearmsnews.com/editori...9-elite/467664

[lysander]

Regarding 4340, the Turkish BRG-9 Elite handgun is advertised as having the barrel and slide made from this grade of steel. Don't know if they're unique in this or if there are other handguns with similar specs.

"They then subject the slide and barrel to a double heat-*treatment process. That is done to produce a harder surface while maintaining a tough core or interior, which keeps hard parts from being perhaps a bit brittle. In effect, you get the surface hardness of a 4350, and they get the machinability of the 4340 alloy. This is not a new idea, it has been done for over a century in manufacturing, but it does take extra time, steps and equipment, so hats off to Burgu for going those extra steps for our benefit."

https://www.firearmsnews.com/editori...9-elite/467664

Sounds like they are induction hardening.

[Diamondback]

Machinability is one of the more overlooked factors, and exotic materials, like titanium, tend to be hard to work with. Now that I have typed that, I am sure there will be a dozen or so comments stating that they machine titanium all the time and have no problem with it . . . Machine a screw from 12L14, then from Grade 5 Titanium, and tell which was easier. And, being an exotic alloy is not the determining factor in machinability, some mild steels are a pain to work with as they tend to gum up the tool.

EDIT - I take it back, M2 and M85 breech bolts are made from 4340 . . .

Book Reco: Ben Rich, "Skunk Works." Gives deep detail about just how much of a screaming nightmare Ti was to work with on the Blackbirds.

[Diamondback]

I'm having bolts custom fabricated from tamahagane steel.

Meh. Call me when you have Vibranium or Adamantium. :P

[Disciple]

While 4340 can be hardened to a yield strength of 220,000 psi (9310 and 158 in bolts runs around 135,000 psi at the core), with a hardness of RHc 44, it is not considered a good candidate for carburizing, so you are stuck with through hardening which won't give a hard surface, or induction hardening which is not appropriate to the geometry of an AR bolt.

The M2 and M85 bolts have huge bearing surfaces so a super hard surface (RHc 58-60) is not critical, the M2 bolt is only the equivalent of RHc 50.

Since you're apparently in the mood to field these oddball questions here's another one. How about 52100 tempered to 750°F? Not tough enough?