08-14-2013, 07:10 PM
Tedward Wrote:I talkeed to Frank today too and had been talking to him months ago about bolt carriers. As you said he has big deliveries and our needs he wants to help out. He is willing to make the run and put some on the shelf and help out any of these other manufactures who need the 6.5 Type II bolts. It's just an upfront expense and he doesn't want any money from us, just wants to make sure others don't do the same think he is going to do. So that being said, he will let us know Monday as to what the company will do.
He did log onto the forum and read everyone's comments and concerns. I asked him to sign up so if your reading this just join in on the fun Frank....
One thing was told to me is the material used on the enhanced bolts is 9310 which is harder/stronger than the Carpenter 158 used on other carrier parts and less powerful cartridges. Due to the Grendel pressures of 50,000psi and people hand-loading a hot load, the bolt needs to be rated a little higher, 62,000psi or so. That is why the Carpenter 158 had issues and the "Enhanced Bolt" was made. I am pretty sure the main difference was the material, 9310.
If someone know's exactly the specs. for the material used on the Grendel Bolts, please confirm what I said is correct. Frank is willing to use what ever material we need.
LOG ON FRANK.....
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.