Extractor Marks?
- Thread starter MT257
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I know I'm probably late here, and you likely got your answer already, but figured I've give my take on excessive pressure signs as it applies to this post.
Primers are one way to watch for excessive pressure, because they do react to it first and the most, as far as physical changes in appearance. That said, they are notorious for producing false signs of pressure. They're softer than the head of the case, and they're simply friction seated into the pocked on the case head, rather than one solid piece like the actual case. Under 50-70k psi of pressure, the primers will unseat themselves under the pressure of the round firing, the case will expand too, and as everything expands to fill the voids in the chamber the case head also fills the void against your bolt face. That reseats the primer. The immense pressure will allow the metal of the primer cup to literally flow and that's what results in it flattening as it reseats against the bolt face.
Sometimes you'll even experience cratering, like you have, but it doesn't necessarily mean it's from excessive pressure. Remington actually purposely makes their firing pin holes on R700's larger and puts a slight bevel around it so that you will see cratering first when pressure begins to raise. It doesn't necessarily mean your pressures are actually high or excessive, but it means the pressure is high enough to allow the metal to flow. It's more of a safety function they think helps the inexperienced.
If the hole for your firing pin is a significantly larger diameter than your firing pin, you'll experience cratering on your primers. Again, that's due to the metal of the primer cup flowing into the space around the firing pin and surrounding the protruding pin. If it's bad enough, it can flow to the point it thins out around the pin and will allow the pin to pierce the primer (called blanking). This is still not necessarily a sign of excessive pressure. It's more just a sign of a bad fit of your firing pin to your bolt face (the firing pin hole is just too large).
When the brass of the case itself begins to flow, especially to the point it pushes the lugs of your bolt hard against your action, making the lift of your bolt handle harder (more resistance than opening it with an unfired round), that's when pressure is excessive and you need to back it off a bit. This is also referred to as sticky bolt. If you can read your case stamp on your bolt face, it's on the hot side.
If you wanted to fix the cratering, simply get your bolt face bushed to ensure there's no gap/void between your firing pin and firing pin hole in your bolt face.
And yes, some primers are softer than others. That's another reason to not trust primers alone for signs of excessive pressure. Just take note of how the primer looks when you start getting a sticky bolt. If you're trying new primers, take note of each type at that stage. They'll likely all look a bit different. That'll help you later easily reference the primers for changes in pressure caused by things like temps fluctuating.
Look for signs on the case head too. As the metal of the case also begins to flow under pressure, it'll fill any voids it can as well. The hole the ejector plunger recesses into on your bolt face is the most common place the case head flows into. It'll leave a mark on the case head when that happens. Any marks left by the extractor are referred to as a swipe. When these swipes and ejector marks are pronounced, your pressures are getting high, your bolt handle lift should be experiencing resistance soon, if not already, at that point.
Another way to check for signs of excessive pressure is to take your calipers and measure the diameter of your extractor groove on an unfired case, then measure it again after it's fired and see what the difference is, if any. If you're seeing a big change, that's a sign of excessive pressure.
Hopefully this proves helpful.
Primers are one way to watch for excessive pressure, because they do react to it first and the most, as far as physical changes in appearance. That said, they are notorious for producing false signs of pressure. They're softer than the head of the case, and they're simply friction seated into the pocked on the case head, rather than one solid piece like the actual case. Under 50-70k psi of pressure, the primers will unseat themselves under the pressure of the round firing, the case will expand too, and as everything expands to fill the voids in the chamber the case head also fills the void against your bolt face. That reseats the primer. The immense pressure will allow the metal of the primer cup to literally flow and that's what results in it flattening as it reseats against the bolt face.
Sometimes you'll even experience cratering, like you have, but it doesn't necessarily mean it's from excessive pressure. Remington actually purposely makes their firing pin holes on R700's larger and puts a slight bevel around it so that you will see cratering first when pressure begins to raise. It doesn't necessarily mean your pressures are actually high or excessive, but it means the pressure is high enough to allow the metal to flow. It's more of a safety function they think helps the inexperienced.
If the hole for your firing pin is a significantly larger diameter than your firing pin, you'll experience cratering on your primers. Again, that's due to the metal of the primer cup flowing into the space around the firing pin and surrounding the protruding pin. If it's bad enough, it can flow to the point it thins out around the pin and will allow the pin to pierce the primer (called blanking). This is still not necessarily a sign of excessive pressure. It's more just a sign of a bad fit of your firing pin to your bolt face (the firing pin hole is just too large).
When the brass of the case itself begins to flow, especially to the point it pushes the lugs of your bolt hard against your action, making the lift of your bolt handle harder (more resistance than opening it with an unfired round), that's when pressure is excessive and you need to back it off a bit. This is also referred to as sticky bolt. If you can read your case stamp on your bolt face, it's on the hot side.
If you wanted to fix the cratering, simply get your bolt face bushed to ensure there's no gap/void between your firing pin and firing pin hole in your bolt face.
And yes, some primers are softer than others. That's another reason to not trust primers alone for signs of excessive pressure. Just take note of how the primer looks when you start getting a sticky bolt. If you're trying new primers, take note of each type at that stage. They'll likely all look a bit different. That'll help you later easily reference the primers for changes in pressure caused by things like temps fluctuating.
Look for signs on the case head too. As the metal of the case also begins to flow under pressure, it'll fill any voids it can as well. The hole the ejector plunger recesses into on your bolt face is the most common place the case head flows into. It'll leave a mark on the case head when that happens. Any marks left by the extractor are referred to as a swipe. When these swipes and ejector marks are pronounced, your pressures are getting high, your bolt handle lift should be experiencing resistance soon, if not already, at that point.
Another way to check for signs of excessive pressure is to take your calipers and measure the diameter of your extractor groove on an unfired case, then measure it again after it's fired and see what the difference is, if any. If you're seeing a big change, that's a sign of excessive pressure.
Hopefully this proves helpful.
kirt
Member
To much powder try 66 grs
