Why I Shoot the 30-30 in Benchrest
- Thread starter mturner
- Start date
lose pockets no more!!!!!
The 30/30 brass not getting lose primer pockets makes sense to me, if I understand what I've been reading and its true. I've read when you get lose primer pockets its cause you over pressured the case and the base has expanded enough to let the pocket expand also. The rimmed case has a gusset (the rim) all the way around it to strengthen and keep the base from expanding. Now if my 7mm ultra mag had a rim about as big as a silver dollar, and about 1/4 inch thick I could load em like I want to.
The 30/30 brass not getting lose primer pockets makes sense to me, if I understand what I've been reading and its true. I've read when you get lose primer pockets its cause you over pressured the case and the base has expanded enough to let the pocket expand also. The rimmed case has a gusset (the rim) all the way around it to strengthen and keep the base from expanding. Now if my 7mm ultra mag had a rim about as big as a silver dollar, and about 1/4 inch thick I could load em like I want to.
Oh yea
Maybe I can amp up the ultra mags and when the pockets get bigger I can just use shotgun primers? What do you think? I saw years ago some one on this board had made some bases for a big case out of steel and threaded on the body, shoulder and neck from a standard brass case that had had the base cut off. If I had about 50 of those I could start shooting 162 Amaxes out of the 7RUM at 3600 fps again.
Maybe I can amp up the ultra mags and when the pockets get bigger I can just use shotgun primers? What do you think? I saw years ago some one on this board had made some bases for a big case out of steel and threaded on the body, shoulder and neck from a standard brass case that had had the base cut off. If I had about 50 of those I could start shooting 162 Amaxes out of the 7RUM at 3600 fps again.
Pressure
I realize there has been some joking concerning really hot loads, but at the same time, I would like to go over some facts that I have learned over the years from my own testing, and from experiences that a few others have had. I realize this is somewhat off topic, but important. Make no mistake, I'm just as much about pushing velocities as many others, but we must be cautious.
As a general rule, the case is the weakest link, and for the most part, the case will show signs of excessive pressure. The most common sign is a loose primer pocket. Anyone who has tried pushing velocities beyond what is considered maximum has probably seen this. I will explain later why the case is not always the weakest link, with several examples of the case being strong enough to cause failures with the firearm.
Men are born with a need to get the most performance we can out of whatever toy we own. We get more performance from our engines by running higher compression ratios. When we have pushed the compression as far as we can, because of poor fuel, we look to the camshaft to increase cylinder pressures by changing the duration, lift, or lobe separation angles and centerlines. High flow heads with high port velocities are a must. The more fuel and air we can stuff in the cylinder, the more power.
When it comes to velocity, we naturally look for the weakest link. If the primers show cratering, long before getting loose in the primer pocket, we can reduce the firing pin diameter, increase the striking force, or both. Now that the primer isn't showing the pressure sign, we can increase the pressure until the primer gets loose. We may just have gained 150 fps. from the firing pin modification. Now we need stronger cases, and Lapua is the perfect choice for high tensile strength cases. Now we go up on the load until the primer starts to loosen, and at this point our pressures are in the 85,000 psi range. As long as we then back the load down by a grain or so, the primer pockets will continue to hold the primers snug, and we can shoot these very high velocity loads without any problems in most cases.
Now for some examples of the brass being stronger than the firearm.
The 6PPC at .441" is still not a very large diameter case. This keeps the thrust down, along with the cartridges ability to actually swell the chamber. I have no doubt that you can loosen the primer in a Lapua 220 Russian case. When you step up to the 6BR Lapua case, things start to change. Because of the slight increase in diameter, the case will handle considerably more pressure, and the chamber walls are thinner. I personally ran the test that follows with 6BR Lapua brass.
The chamber was a 22BR in a stainless barrel of 1.2" diameter. I wanted to determine the maximum velocity that could be obtained from a 52gr Sierra before the primer pocket loosened. As I continued to increase the powder charge of W748 by 1/2gr increments, I watched the velocity quickly exceed 4000fps. I continued, because the primer was still tight. At around 39gr of W748 the velocity reached 4152fps. The case was stuck, so I knocked it out with a cleaning rod, and told my friend Dan that we have definitely gone over maximum pressure. I took that case and resized it, and seated a new primer. To my surprise, the primer seated with almost as much effort as a new case. From the primer seating effort I would have said we were just barely over maximum. That would prove to be wrong after further observation. While we had determined the maximum load according to the strenght of the case, we were unaware that the chamber had swelled about .002". We found that out when the next round was fired using a normal pressure load. The case was stuck again. The chamber had a slight reverse taper. We had exceeded the maximum pressure for a 1.2" stainless barrel, and the case was still holding primers tighter than most cheaper brands of brass. The barrel would require a set back and rechamber.
Ross Seyfried had a custom rifle built chambered for a 30-416 Rigby Improved. An action of 1.5" diameter and a Douglas barrel of 1.4" diameter and 34" length was used. The barrel was 1.4" in diameter, not just for accuracy purposes, but also to make sure the chamber would not swell. His load of 127gr of WC872 pushed a 200gr Sierra Matchking at 3650fps. My point is this. These very large diameter cases at very high pressures are capable of swelling chambers in stainless barrels, and produce enough thrust against the bolt to cause action failures. I have built several rifles chambered 30-378 Weatherby, and have seen high pressure signs reveal themselves in many ways, long before the case shows high pressure signs. Keep in mind that chrome-moly barrels have greater tensile strength than stainless barrels.
When I was a teenager living in Sanderson TX, a friend had a Sako chambered in 243 Win. The action blew up from a standard book load. When looking at the action, there was almost no distortion of the steel pieces. They just looked like broken pieces of cast iron. They just looked brittle. I did not have a hardness tester at that time, so I can't say what was really going on. As you know, there have been a few reports of locking lugs falling off BR actions used by the PPC shooters. This would probably be caused by a material problem, or a heat treating problem. The steel used was S7 air hardening shock resisting tool steel. I personally have used S7 for my own actions, and even used it for 454 Casull revolver cylinders, and have never had any reason to doubt it's superior strength properties. This just goes to show you that even when proper steels are used, improper heat treating, steel not being was it was purchased to be, or a stress riser can cause failure.
I have had times in my life where my job was to chronograph various prototype cartridges to determine just how much performance can be obtained. This was not done for fun at all. It was 6 months of continuous chronographing. From the building of prototype firearms, to special purpose cartridge designs, I have done plenty of hot rodding with high pressures, and have seen first hand the effect of high pressure. Have fun, but always be safe.
Michael
I realize there has been some joking concerning really hot loads, but at the same time, I would like to go over some facts that I have learned over the years from my own testing, and from experiences that a few others have had. I realize this is somewhat off topic, but important. Make no mistake, I'm just as much about pushing velocities as many others, but we must be cautious.
As a general rule, the case is the weakest link, and for the most part, the case will show signs of excessive pressure. The most common sign is a loose primer pocket. Anyone who has tried pushing velocities beyond what is considered maximum has probably seen this. I will explain later why the case is not always the weakest link, with several examples of the case being strong enough to cause failures with the firearm.
Men are born with a need to get the most performance we can out of whatever toy we own. We get more performance from our engines by running higher compression ratios. When we have pushed the compression as far as we can, because of poor fuel, we look to the camshaft to increase cylinder pressures by changing the duration, lift, or lobe separation angles and centerlines. High flow heads with high port velocities are a must. The more fuel and air we can stuff in the cylinder, the more power.
When it comes to velocity, we naturally look for the weakest link. If the primers show cratering, long before getting loose in the primer pocket, we can reduce the firing pin diameter, increase the striking force, or both. Now that the primer isn't showing the pressure sign, we can increase the pressure until the primer gets loose. We may just have gained 150 fps. from the firing pin modification. Now we need stronger cases, and Lapua is the perfect choice for high tensile strength cases. Now we go up on the load until the primer starts to loosen, and at this point our pressures are in the 85,000 psi range. As long as we then back the load down by a grain or so, the primer pockets will continue to hold the primers snug, and we can shoot these very high velocity loads without any problems in most cases.
Now for some examples of the brass being stronger than the firearm.
The 6PPC at .441" is still not a very large diameter case. This keeps the thrust down, along with the cartridges ability to actually swell the chamber. I have no doubt that you can loosen the primer in a Lapua 220 Russian case. When you step up to the 6BR Lapua case, things start to change. Because of the slight increase in diameter, the case will handle considerably more pressure, and the chamber walls are thinner. I personally ran the test that follows with 6BR Lapua brass.
The chamber was a 22BR in a stainless barrel of 1.2" diameter. I wanted to determine the maximum velocity that could be obtained from a 52gr Sierra before the primer pocket loosened. As I continued to increase the powder charge of W748 by 1/2gr increments, I watched the velocity quickly exceed 4000fps. I continued, because the primer was still tight. At around 39gr of W748 the velocity reached 4152fps. The case was stuck, so I knocked it out with a cleaning rod, and told my friend Dan that we have definitely gone over maximum pressure. I took that case and resized it, and seated a new primer. To my surprise, the primer seated with almost as much effort as a new case. From the primer seating effort I would have said we were just barely over maximum. That would prove to be wrong after further observation. While we had determined the maximum load according to the strenght of the case, we were unaware that the chamber had swelled about .002". We found that out when the next round was fired using a normal pressure load. The case was stuck again. The chamber had a slight reverse taper. We had exceeded the maximum pressure for a 1.2" stainless barrel, and the case was still holding primers tighter than most cheaper brands of brass. The barrel would require a set back and rechamber.
Ross Seyfried had a custom rifle built chambered for a 30-416 Rigby Improved. An action of 1.5" diameter and a Douglas barrel of 1.4" diameter and 34" length was used. The barrel was 1.4" in diameter, not just for accuracy purposes, but also to make sure the chamber would not swell. His load of 127gr of WC872 pushed a 200gr Sierra Matchking at 3650fps. My point is this. These very large diameter cases at very high pressures are capable of swelling chambers in stainless barrels, and produce enough thrust against the bolt to cause action failures. I have built several rifles chambered 30-378 Weatherby, and have seen high pressure signs reveal themselves in many ways, long before the case shows high pressure signs. Keep in mind that chrome-moly barrels have greater tensile strength than stainless barrels.
When I was a teenager living in Sanderson TX, a friend had a Sako chambered in 243 Win. The action blew up from a standard book load. When looking at the action, there was almost no distortion of the steel pieces. They just looked like broken pieces of cast iron. They just looked brittle. I did not have a hardness tester at that time, so I can't say what was really going on. As you know, there have been a few reports of locking lugs falling off BR actions used by the PPC shooters. This would probably be caused by a material problem, or a heat treating problem. The steel used was S7 air hardening shock resisting tool steel. I personally have used S7 for my own actions, and even used it for 454 Casull revolver cylinders, and have never had any reason to doubt it's superior strength properties. This just goes to show you that even when proper steels are used, improper heat treating, steel not being was it was purchased to be, or a stress riser can cause failure.
I have had times in my life where my job was to chronograph various prototype cartridges to determine just how much performance can be obtained. This was not done for fun at all. It was 6 months of continuous chronographing. From the building of prototype firearms, to special purpose cartridge designs, I have done plenty of hot rodding with high pressures, and have seen first hand the effect of high pressure. Have fun, but always be safe.
Michael
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