09-28-2011, 05:13 PM
I've always felt that the standard AR15 bolt geometry was too wimpy for even 5.56, which is already on the edge of max pressures by design. The original objectives of the Small Caliber, High Velocity Rifle was 3400 fps with light projectiles, but they realized they were pushing way too far with the pressures. They wanted to extend the explosive lead shower effect on tissue that SCHV projectiles exhibit when going over 2600 fps. Even after lowering the pressures to 55,000 psi, the AR15 was and is a very high-pressure system with a low-mass bolt, with wall thicknesses on the sketchy side of logical in my book. The .270 Winchester max's out around 51,000 psi, for comparison.
On the other hand, if you look at an AR10 bolt, it is really well-built, and hefty. I was surprised recently when looking at an FN SCAR 7.62 bolt after breaking it down-It had a wimpy little bolt with thin walls, but was made of some different type of steel alloy, which showed early signs of surface corrosion. I wonder how long it will be before they start letting go, or if the alloy will take a beating of repeated 7.62 in high-volume.
On the other hand, if you look at an AR10 bolt, it is really well-built, and hefty. I was surprised recently when looking at an FN SCAR 7.62 bolt after breaking it down-It had a wimpy little bolt with thin walls, but was made of some different type of steel alloy, which showed early signs of surface corrosion. I wonder how long it will be before they start letting go, or if the alloy will take a beating of repeated 7.62 in high-volume.