LRRPF52 Wrote:Nobody should be loading for the Grendel in the AR15 past the maximum published loads. 62,000psi is about 10,000 psi more than max loads. The bolt thrust and bolt geometry of the AR15 bolt barely support 62,000psi pressures that long in 5.56 NATO.

The original AR15 bolt geometry was built around a 50,000psi SAAMI max cartridge, the .222 Remington. When that evolved into the 5.56x45 (and civvy version .223 Rem), the pressures were raised significantly, without what I feel should have generated an engineering and blueprint change for the whole system. Since it would have only changed dimensions by maybe 2/10's of an inch, it wasn't pursued. (new bolt, new extension, new magazine, new upper)

Carpenter 158 was specifically selected for the military bolts because it could handle the higher pressures better than 8620, but they also added the High Pressure Test load, followed by Magnetic Particle Inspection (HPT/MPI) to see if microscopic stress fractures had been induced by the HPT load.

Carpenter 158 is very difficult for a shop to get, as you have to order high volumes of it. It is an excellent steel for AR15 bolts. Harder does not mean stronger, especially when you look at shock force on a steel part. You want a balance of substrate ductility, with great surface hardness, and a steel that takes heat-treating well without the surface becoming too brittle. If it is so hard that it fractures on the surface, you will start cracking bolt lugs or the cam pin hole walls.

Frank is very aware of these things, and has been dealing with AR15 BCG's as an OEM supplier for a long time. In the end, engineers will most likely be involved with selecting the optimum bolt material, dimensions, and heat treating, as well as extractor steel.

cory Wrote:While this is true, the bolt still needs to be designed with a Factor of Safety (FoS).
Factor of Safety=Ultimate Load/Allowable Load

I've read here before were Bill A had said he had to proof test the bolts to 62ksi. This gives us a FoS of 1.19.

Quote:We are currently making bolts for a very large AR-15 manufacturer. I have had several other smaller firearms companys contact me looking to purchase these bolts. But the material that we are currently using is supplied to us by our customer. The Carpenter 158 has to be purchased in 20,000 Lb lots and is roughly $5/Lb.

Sputnik Wrote:I think you will find many people that will disagree. Business decision? Price gouging a business decision; but it isn't right. AA didn't do it. Now, I have never met Mr. Bill Alexander, but he seems to be a man of impeccable integrity! When he or his representatives say they fill orders in the "first come first served" method, all we can do is take him for his word. A man's word is his bond. ...

LRRPF52 Wrote:http://www.practicalmachinist.com/vb/general/alternate-material-carpenter-158-a-199836/

That link answers a lot of the questions right off the bat. The main one is that Carpenter 158 is basically inaccessible to many smaller manufacturers, because of ordering volume requirements and cost. Here's the quote that jumped out to me right off the bat, and confirms what I have learned about the AR15 industry especially over the years:



That means, for a machine shop to use Carpenter 158, they have a minimum volume order of $100,000. At this point, we're basically diving into areas of materials selection that most machine shops and rifle manufacturers rarely discuss, for several reasons that are obvious to the savvy engineer, as well as machinist and businessman.

I can tell you that after speaking with Frank, and the steels he has regular access to, we are in great hands, and probably need not worry too much about it. Also, roger that on the Factor of Safety. The bolts need to be able to handle proof loads of no less than 62,000psi, although my understanding is that AA's hard use bolt does that and more with ease.

With 9310, I think phosphorous is the main enemy, but I'm not an engineer.

Tedward Wrote:So I think Frank is the best to use what he knows as a superior material to provide us a superior product he will stand behind. That being said, did he tell you what he feels would be the best to use??

LRRPF52 Wrote:http://www.practicalmachinist.com/vb/general/alternate-material-carpenter-158-a-199836/

That link answers a lot of the questions right off the bat. The main one is that Carpenter 158 is basically inaccessible to many smaller manufacturers, because of ordering volume requirements and cost. Here's the quote that jumped out to me right off the bat, and confirms what I have learned about the AR15 industry especially over the years:



That means, for a machine shop to use Carpenter 158, they have a minimum volume order of $100,000. At this point, we're basically diving into areas of materials selection that most machine shops and rifle manufacturers rarely discuss, for several reasons that are obvious to the savvy engineer, as well as machinist and businessman.

I can tell you that after speaking with Frank, and the steels he has regular access to, we are in great hands, and probably need not worry too much about it. Also, roger that on the Factor of Safety. The bolts need to be able to handle proof loads of no less than 62,000psi, although my understanding is that AA's hard use bolt does that and more with ease.

With 9310, I think phosphorous is the main enemy, but I'm not an engineer.

Ridgerider Wrote:Well not quit I just found this http://www.industrialmetalsales.com/3-4-Diameter-Carpenter-158-Round-Bar_c379.htm

explorecaves Wrote:Did you read the link I posted regarding the phosphorus in nickel alloy? The conclusions drawn indicate the lower the phosphorus content, the less cracking there is. Since the 9310 contains a MAX 0.025% (could be less) and the AISI is mandated to be 0.03%.....

XcountryRider Wrote:Just talked to Frank they are going to use 9130 and he already has a customer of the bolts that requested 9130.

XcountryRider Wrote:Just talked to Frank they are going to use 9130 and he already has a customer of the bolts that requested 9130.

cory Wrote:Great. Any ETA on the first bolt?

Tedward Wrote:Confused, what do you mean by " he already has a customer of the bolts that requested 9130." Sort of doesn't make sense...do you mean he has a customer who requested 9130??

I hope you meant 9310...

XcountryRider Wrote:Yes and yes.