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Rifles, Reloading, Optics, Equipment
Reloading
primer cratering 7mm ultra mag
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<blockquote data-quote="Fiftydriver" data-source="post: 180009" data-attributes="member: 10"><p>Take your bolt out of your rifle, let the cocking piece on the back of the bolt turn to lower the firing pin and then with your calipers measure the diameter of the firing pin sticking out the hole in the bolt face.</p><p> </p><p>I am about 95% sure your problem is simply that the firing pin is oversized. Firing pins for modern, high pressure magnums should in reality be no larger then 0.062" in diameter. Why there are no rifle makers that seem to understand this is beyond me as they are still using firing pins that would be more at home on a black powder or lever action from 100 years ago where chamber pressures are very low in comparision.</p><p> </p><p>What happens, most factory firing pins will run from 75 to even 80 thou in diameter, this is simply way to large in diameter. When the pressure builds after the powder in the case ignites, it pushes back on the bolt face and also the primer cup. The primer cup is relatively thin and weak. It can not support the pressure over a large firing pin diameter area. Because of this, this portion of the primer cup is forced back by the chamber pressure which pushed the firing pin nose back into the bolt face.</p><p> </p><p>The primer cup material follows the firing pin into the firing pin hole, as such, you get primer cratering.</p><p> </p><p>so what do you do about it, well, unless you plug the firing pin hole, refinish the bolt face surface and then redrill the firing pin hole to roughly 64 thou diameter and fit a 62 thou diameter firing pin, thats about the only cure to prevent this.</p><p> </p><p>Thats the bad news, the good news, as long as the cratered cup on the primer has rounded edges and not sharp you are not in any trouble. If this crater starts getting sharp on the edges it means the primer pocket material is actually shearing under the pressure and primer piercing is close at hand.</p><p> </p><p>If the edges are rounded, your well under the level where you will see piercing.</p><p> </p><p>Simply put, its really nothing to worry about, just a problem with the rifle makers making the firing pin to large but no real problem will result from it as long as you do not overload your ammo.</p><p> </p><p>Winchesters are famous for this. Savages can be nearly as bad. Remingtons are generally not as bad but you see it often still.</p><p> </p><p>I would be nearly positive this is your problem so meaure your firing pin diameter and that will tell you alot. If the firing pin is not oversized but the firing pin hole is, you still have the same problem.</p><p> </p><p>Kirby Allen(50)</p></blockquote><p></p>
[QUOTE="Fiftydriver, post: 180009, member: 10"] Take your bolt out of your rifle, let the cocking piece on the back of the bolt turn to lower the firing pin and then with your calipers measure the diameter of the firing pin sticking out the hole in the bolt face. I am about 95% sure your problem is simply that the firing pin is oversized. Firing pins for modern, high pressure magnums should in reality be no larger then 0.062" in diameter. Why there are no rifle makers that seem to understand this is beyond me as they are still using firing pins that would be more at home on a black powder or lever action from 100 years ago where chamber pressures are very low in comparision. What happens, most factory firing pins will run from 75 to even 80 thou in diameter, this is simply way to large in diameter. When the pressure builds after the powder in the case ignites, it pushes back on the bolt face and also the primer cup. The primer cup is relatively thin and weak. It can not support the pressure over a large firing pin diameter area. Because of this, this portion of the primer cup is forced back by the chamber pressure which pushed the firing pin nose back into the bolt face. The primer cup material follows the firing pin into the firing pin hole, as such, you get primer cratering. so what do you do about it, well, unless you plug the firing pin hole, refinish the bolt face surface and then redrill the firing pin hole to roughly 64 thou diameter and fit a 62 thou diameter firing pin, thats about the only cure to prevent this. Thats the bad news, the good news, as long as the cratered cup on the primer has rounded edges and not sharp you are not in any trouble. If this crater starts getting sharp on the edges it means the primer pocket material is actually shearing under the pressure and primer piercing is close at hand. If the edges are rounded, your well under the level where you will see piercing. Simply put, its really nothing to worry about, just a problem with the rifle makers making the firing pin to large but no real problem will result from it as long as you do not overload your ammo. Winchesters are famous for this. Savages can be nearly as bad. Remingtons are generally not as bad but you see it often still. I would be nearly positive this is your problem so meaure your firing pin diameter and that will tell you alot. If the firing pin is not oversized but the firing pin hole is, you still have the same problem. Kirby Allen(50) [/QUOTE]
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primer cratering 7mm ultra mag
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