04-20-2014, 03:36 AM
Projectiles with more of a secant ogive can get mis-aligned in the bore if they jump too much at Grendel pressures in the AR15. That kind of jump equals bad accuracy, unless you load tangent ogive pills as far out as the magazine will allow, like the 130gr Sierra Game King, the 85gr Sierra HP, pills like that. Then some will say, "Just drive the projectile faster into the lands with more pressure."
Ramp up the pressures, and the barrel tennon stretches too much. Arne even stated clearly that it's better to steer clear of the heavier 140gr pills in the Grendel, as pressure can sneak up on you quickly.
All this aside, when I look at SAAMI chamber performance through the scope at distance, I have zero reason to own a .308 any more, and have seen many people come to this same conclusion after being ardent holders to the .308 Win. Many will still keep both, but I personally have no reason to. That is a huge performance advantage to me that saves me literally thousands of dollars.
This .264 version 5.0 BS is just another way of people with a chip on their shoulder to try to ruin the cartridge. It's basically a knee jerk from short chamber to long chamber with all kinds of jump. If you look at the short chambered pipes, they consistently were shooting amazing little groups, blown and pierced primers aside, because the projectiles had no room to get off center, and the pressures are consistently higher, way beyond SAAMI Maximum Average Mean even (it takes a lot of pressure to blow or pierce a primer, usually 60-70ksi and higher depending on the primer).
The gun will take that a few times, but then things start to change permanently in the chamber if the bolt hasn't given out yet. The actual Grendel chamber is a fine balance between consistent accuracy across projectile shapes, and the rated pressures keep it safe. Some consider this "handicapping" the cartridge, and want to push the pressures more and more, but the real constraint is in the dimensions of the barrel tennon, barrel extension, and upper receiver which were all built around the .222 Remington. I don't think many people have a handle on how important it was for the engineers at Armalite to really make a lightweight rifle.
It has taken me a long time to realize the importance of the diameters, while looking past the strength of the bolt. It will be interesting to see what happens with the AR-Stoner/Liberty barrels that made it out into the market, as people build round counts on them. The ones that were blowing & piercing primers with factory ammo scream something wrong right off the bat, and will get immediate attention from all but the most unobservant mouth breathers.
...but the ones that really will be problematic are the ones that are short-chmabered, but still allow factory ammo to chamber and fire repeatedly at higher pressures than the SAAMI Maximum Average Mean (55ksi), not the Maximum Average Pressure (52ksi). You can fire factory ammo all day long at over 55ksi, as long as the bolt will take it (properly made bolts from good alloys will with a trued/squared system will do it for the life of the barrel), but will the chamber?
The walls are not that thick where the barrel tennon is. This is why we like to stay at 50,000psi. Delta tested the 6.8 SPC in high volume, and concluded it was dangerous because of this, and they have teams of engineers who are from aerospace backgrounds, who know materials strengths like the backs of their hands. You can't enlarge the chamber of the AR15 barrel (Reducing the thickness of the steel) AND ramp up or match the pressures of 5.56 NATO and expect everything to be peachy. I've said for years that even 5.56 is a shoe horn into the AR15-it was literally never meant for the 5.56 NATO, and I have seen plenty of 5.56 bolts broken, and broken one myself in a high volume gun at 10,000rds.
This chamber seems like an easy manufacturing approach, where a shop with poor QC can crank them out and let the reamer wear down, while not encroaching into the space for the projectile.
Ramp up the pressures, and the barrel tennon stretches too much. Arne even stated clearly that it's better to steer clear of the heavier 140gr pills in the Grendel, as pressure can sneak up on you quickly.
All this aside, when I look at SAAMI chamber performance through the scope at distance, I have zero reason to own a .308 any more, and have seen many people come to this same conclusion after being ardent holders to the .308 Win. Many will still keep both, but I personally have no reason to. That is a huge performance advantage to me that saves me literally thousands of dollars.
This .264 version 5.0 BS is just another way of people with a chip on their shoulder to try to ruin the cartridge. It's basically a knee jerk from short chamber to long chamber with all kinds of jump. If you look at the short chambered pipes, they consistently were shooting amazing little groups, blown and pierced primers aside, because the projectiles had no room to get off center, and the pressures are consistently higher, way beyond SAAMI Maximum Average Mean even (it takes a lot of pressure to blow or pierce a primer, usually 60-70ksi and higher depending on the primer).
The gun will take that a few times, but then things start to change permanently in the chamber if the bolt hasn't given out yet. The actual Grendel chamber is a fine balance between consistent accuracy across projectile shapes, and the rated pressures keep it safe. Some consider this "handicapping" the cartridge, and want to push the pressures more and more, but the real constraint is in the dimensions of the barrel tennon, barrel extension, and upper receiver which were all built around the .222 Remington. I don't think many people have a handle on how important it was for the engineers at Armalite to really make a lightweight rifle.
It has taken me a long time to realize the importance of the diameters, while looking past the strength of the bolt. It will be interesting to see what happens with the AR-Stoner/Liberty barrels that made it out into the market, as people build round counts on them. The ones that were blowing & piercing primers with factory ammo scream something wrong right off the bat, and will get immediate attention from all but the most unobservant mouth breathers.
...but the ones that really will be problematic are the ones that are short-chmabered, but still allow factory ammo to chamber and fire repeatedly at higher pressures than the SAAMI Maximum Average Mean (55ksi), not the Maximum Average Pressure (52ksi). You can fire factory ammo all day long at over 55ksi, as long as the bolt will take it (properly made bolts from good alloys will with a trued/squared system will do it for the life of the barrel), but will the chamber?
The walls are not that thick where the barrel tennon is. This is why we like to stay at 50,000psi. Delta tested the 6.8 SPC in high volume, and concluded it was dangerous because of this, and they have teams of engineers who are from aerospace backgrounds, who know materials strengths like the backs of their hands. You can't enlarge the chamber of the AR15 barrel (Reducing the thickness of the steel) AND ramp up or match the pressures of 5.56 NATO and expect everything to be peachy. I've said for years that even 5.56 is a shoe horn into the AR15-it was literally never meant for the 5.56 NATO, and I have seen plenty of 5.56 bolts broken, and broken one myself in a high volume gun at 10,000rds.
This chamber seems like an easy manufacturing approach, where a shop with poor QC can crank them out and let the reamer wear down, while not encroaching into the space for the projectile.