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

[shadowspirit]

The very recent thread about law enforcement using M&P15s and the discussion about metals and aluminum gave me the idea for this thread.

The bolt in bolt carrier groups vary in quality depending on who is making them and what metal is being used. Good quality bolts can go many rounds before it breaks.

Wouldn't it be a good idea for a manufacturer to make a bolt out of titanium or some other exotic metal that lasts far longer than current high quality bolts? People would buy them unless the price wasn't extreme. Also, it would be a good marketing tool for the "gucci" brand ARs that they have the latest and greatest bolts.

I guess the above may be a good idea for other parts of the BCG like the extractor and spring.

[DoubleW]

Given that a properly maintained bolt can lasts tens of thousands of rounds (more than most people shoot in a lifetime) there’s really no point. The only appeal something like a ti bolt would have is its weight. I doubt it would actually be more durable. Lastly, most people seek to add weight to the reciprocating bits of their rifle, so the addition of a lighter bolt or bcg would then require a correspondingly heavier buffer. They’ve pretty much perfected bolts as they are. If anything, more manufacturers should radius the lugs like KAC and LMT do in order to eliminate stress risers.

[Todd.K]

Bolt material is chosen for core strength and surface hardness.

Titanium does not surface harden, it’s actually pretty soft so the lugs would deform.

[MegademiC]

Ti would be terrible. Steel is really good for that application. The best way to enhance is with geometry changes like KAC did.

[1168]

https://www.m4carbine.net/showthread...lts&highlight=

[lysander]

AISI 4340 has a higher ultimate and yield strength than both Carpenter 158 and 9310, yet nobody make small arms bolts out of it. There are hundreds of steel alloys, each with dozens of different heat treating options, resulting in essentially over 10,000 different steels. Each are formulated for specific applications.

And there are many more properties that just strength. As stated in that other thread, 6061 is as strong, and 7075 is much stronger, than the structural steel used for buildings and bridges. No 7075 road bridges, even though it would be more corrosion resistant to boot.

I am sure if you when over all the available alloys, you could find something that is stronger, more wear resistant, has a better fatigue life, not brittle, etc. But, it will not be 1) cheaper, or 2) easier to work with, because if it were, everybody would be using it.

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 . . .

[SteyrAUG]

I'm having bolts custom fabricated from tamahagane steel.

[jackblack73]

Geissele offers a bolt made of Carpenter 465. I’m sure there are other companies that also offer bolts made of other exotic metals. But they’re extremely expensive and the average person won’t shoot enough to break a Carpenter 158 or 9310 bolt anyway.

[shadowspirit]

Bolt material is chosen for core strength and surface hardness.

Titanium does not surface harden, it’s actually pretty soft so the lugs would deform.

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

Ti would be terrible. Steel is really good for that application. The best way to enhance is with geometry changes like KAC did.

This is a good specific example of what people mean when they refer to some newer AR traits/designs being better than mil-spec.

How much better is KAC's bolt than mil-spec?

[shadowspirit]

AISI 4340 has a higher ultimate and yield strength than both Carpenter 158 and 9310, yet nobody make small arms bolts out of it. There are hundreds of steel alloys, each with dozens of different heat treating options, resulting in essentially over 10,000 different steels. Each are formulated for specific applications.

And there are many more properties that just strength. As stated in that other thread, 6061 is as strong, and 7075 is much stronger, than the structural steel used for buildings and bridges. No 7075 road bridges, even though it would be more corrosion resistant to boot.

I am sure if you when over all the available alloys, you could find something that is stronger, more wear resistant, has a better fatigue life, not brittle, etc. But, it will not be 1) cheaper, or 2) easier to work with, because if it were, everybody would be using it.

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 . . .

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.