The barrel extension is not the weak link, the barrel tenon is. The MAP for Grendel is between 50-52ksi, but I personally like to stay nearer to 50k. Yes the case can handle 60ksi, but the barrel tenon should not be subjected to that without a total redesign.
Running 60ksi in gas guns has proven to be very hard on self-loaders, as we have seen with the M4 pushing certain loads. It trashes the guns.
Running my .260 Rem AR10 at those pressures has resulted in at least 4 bent firing pin retaining pins, pierced and blown primers, violent recoil that felt like if I shot certain loads again, it would break the rear out of the extension tube...and the .260 Rem AR10 has much more room to play with pressure than the AR15 does. If you read JP's recommendations on hand loading for the AR10 in 6.5mm, he basically says you need to operate at much lower pressures if you want things to stay stable, and factory ammo is a no-go.
Looking at the overall system, how do you balance reciprocating mass, extractor life, throat life, and other critical parts with performance? Something has to give somewhere. You can get a few hundred rounds of top-end .260 Rem performance with the AR10, and then your throat is toast, bolt face looks like the surface of the moon, recoil spring is toast, gas port is eroding, and your extractor needs to be very well engineered to take a beating.
With guys who are wise beyond their years, like George Gardner, I'm seeing a trend where lower pressures are being sought for throat life in bolt guns even, and that's one of the key principles behind the 6.5 SAUM. Yeah, they could run it at nuclear magnum pressures and push a 130gr Berger at 3400fps, but why torch the throat when you can still get 3150fps at 55,000psi?
This is one of the things that has really grown on me with the 6.5 Grendel, and that is this: We are in a very comfortable place for rifle longevity, performance, low recoil, and predictable gas system behavior with factory ammunition. With my .260 Remington, none of that is true. Performance is awesome, if you like being on the ragged edge, otherwise you really need to take a step back and ask what's important to you, and how often you plan to replace premium barrels. I have gone through more replacement parts with the .260 Rem. AR10 than any other caliber, over a lower round count. Gas system signature is on the edge, and some loads have burned powder even into the gas tube, to the point where clouds of smoke literally were pouring out from the seams between the upper and lower, after an extremely violent recoil impulse. That was during load development with a certain slow burning powder from Accurate pushing 140gr A-MAX IIRC, or 142gr SMK.
The Grendel can't sustain a burn as long as a .260 Remington can, because of case capacity. That said, it still does amazingly well when you compare the 2 for supersonic reach. I actually prefer the predictable behavior of a mid-to-lower 2000fps range for close-in shots than a 2800-2900fps mv from the .260 Rem., since I've seen what that does, and it is devastating to meat if using cup and core pills, like a .270 Win. does. A .260 Rem. or .270 Win. is downright explosive at close range. They make perfect antelope rifles, since pronghorns rarely let you get in on them within 400yds, but you really need to watch the bullet construction or think about head and neck shots for close range with the super fast rifles.
When I look at what my little 16" Grendel is already doing with a 123gr using CFE, and not even pushing the pressures at 2500fps, from a practical standpoint, clarity sinks in that it's best to find that accuracy node, and get as much trigger time with it as possible at moderate pressures. I could probably run the gun ragged at 2625fps with a 123gr, but at what benefits and costs? Looking at the drop and drift, it isn't that huge of an advantage, and if I want to be competitive with a .260 Rem, I can use the 22" Grendel and push the 123gr at 2660-2700fps with CFE. The moment we start trying to push 60k in any rifle, the throat, barrel, and brass life drop radically.
Running 60ksi in gas guns has proven to be very hard on self-loaders, as we have seen with the M4 pushing certain loads. It trashes the guns.
Running my .260 Rem AR10 at those pressures has resulted in at least 4 bent firing pin retaining pins, pierced and blown primers, violent recoil that felt like if I shot certain loads again, it would break the rear out of the extension tube...and the .260 Rem AR10 has much more room to play with pressure than the AR15 does. If you read JP's recommendations on hand loading for the AR10 in 6.5mm, he basically says you need to operate at much lower pressures if you want things to stay stable, and factory ammo is a no-go.
Looking at the overall system, how do you balance reciprocating mass, extractor life, throat life, and other critical parts with performance? Something has to give somewhere. You can get a few hundred rounds of top-end .260 Rem performance with the AR10, and then your throat is toast, bolt face looks like the surface of the moon, recoil spring is toast, gas port is eroding, and your extractor needs to be very well engineered to take a beating.
With guys who are wise beyond their years, like George Gardner, I'm seeing a trend where lower pressures are being sought for throat life in bolt guns even, and that's one of the key principles behind the 6.5 SAUM. Yeah, they could run it at nuclear magnum pressures and push a 130gr Berger at 3400fps, but why torch the throat when you can still get 3150fps at 55,000psi?
This is one of the things that has really grown on me with the 6.5 Grendel, and that is this: We are in a very comfortable place for rifle longevity, performance, low recoil, and predictable gas system behavior with factory ammunition. With my .260 Remington, none of that is true. Performance is awesome, if you like being on the ragged edge, otherwise you really need to take a step back and ask what's important to you, and how often you plan to replace premium barrels. I have gone through more replacement parts with the .260 Rem. AR10 than any other caliber, over a lower round count. Gas system signature is on the edge, and some loads have burned powder even into the gas tube, to the point where clouds of smoke literally were pouring out from the seams between the upper and lower, after an extremely violent recoil impulse. That was during load development with a certain slow burning powder from Accurate pushing 140gr A-MAX IIRC, or 142gr SMK.
The Grendel can't sustain a burn as long as a .260 Remington can, because of case capacity. That said, it still does amazingly well when you compare the 2 for supersonic reach. I actually prefer the predictable behavior of a mid-to-lower 2000fps range for close-in shots than a 2800-2900fps mv from the .260 Rem., since I've seen what that does, and it is devastating to meat if using cup and core pills, like a .270 Win. does. A .260 Rem. or .270 Win. is downright explosive at close range. They make perfect antelope rifles, since pronghorns rarely let you get in on them within 400yds, but you really need to watch the bullet construction or think about head and neck shots for close range with the super fast rifles.
When I look at what my little 16" Grendel is already doing with a 123gr using CFE, and not even pushing the pressures at 2500fps, from a practical standpoint, clarity sinks in that it's best to find that accuracy node, and get as much trigger time with it as possible at moderate pressures. I could probably run the gun ragged at 2625fps with a 123gr, but at what benefits and costs? Looking at the drop and drift, it isn't that huge of an advantage, and if I want to be competitive with a .260 Rem, I can use the 22" Grendel and push the 123gr at 2660-2700fps with CFE. The moment we start trying to push 60k in any rifle, the throat, barrel, and brass life drop radically.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com