If you're seeing moderate to excessive case head swipe, it could be an ammo problem, a gun problem or both. But is it serious? Barring another sign of high pressure, such as excessive velocities for your barrel length and failures to feed, minimal CHS is probably not dangerous. Keep in mind, softer brass used by some manufacturers can exaggerate CHS. It's fairly common for many AR-15s and AR-10s to show minimal CHS with some pressure-safe loads.
A blown primer is generally considered a true sign of high pressure, but according to Nosler, it's not always the case with an AR. In severe cases of improper timing, the same circumstances that can cause CHS allow the primer cup to move rearward in the primer pocket, compromising the seal. The primer doesn't fall out until the case is ejected, and usually ends up in the trigger housing. A blown primer may not be a true indication of high pressure, but it is a definite sign of a problem that needs to be addressed. I treat a blown primer as a sign of high pressure and suggest you do the same.
CHS can randomly appear because peak pressure and velocity can vary a great deal between rounds out of the same lot—as much as 4,000 psi and more than 100 fps. This is a good reason to select loads that produce consistent velocities.
Excessive CHS can mar case heads so badly they won't fit into the shell holder when handloading. Back the powder charge down or switch powders, maybe even primers.
Another way to correct CHS is to alter the AR's timing. Switch to a heavier buffer spring, weight the buffer or install an adjustable gas block—or any combination thereof. However, don't assume that because certain loads show no case-head swipe in one AR, they will perform the same in another. The length/size of the gas tube and the size of the gas port can be different. Buffer spring strength and buffer weight can vary, too.
Good article MeltingFeather
A blown primer is generally considered a true sign of high pressure, but according to Nosler, it's not always the case with an AR. In severe cases of improper timing, the same circumstances that can cause CHS allow the primer cup to move rearward in the primer pocket, compromising the seal. The primer doesn't fall out until the case is ejected, and usually ends up in the trigger housing. A blown primer may not be a true indication of high pressure, but it is a definite sign of a problem that needs to be addressed. I treat a blown primer as a sign of high pressure and suggest you do the same.
CHS can randomly appear because peak pressure and velocity can vary a great deal between rounds out of the same lot—as much as 4,000 psi and more than 100 fps. This is a good reason to select loads that produce consistent velocities.
Excessive CHS can mar case heads so badly they won't fit into the shell holder when handloading. Back the powder charge down or switch powders, maybe even primers.
Another way to correct CHS is to alter the AR's timing. Switch to a heavier buffer spring, weight the buffer or install an adjustable gas block—or any combination thereof. However, don't assume that because certain loads show no case-head swipe in one AR, they will perform the same in another. The length/size of the gas tube and the size of the gas port can be different. Buffer spring strength and buffer weight can vary, too.
Good article MeltingFeather
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