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Thank you for clarifying that. I started there but it's been awhile. I think it's an entry point into a development program or general guideline, not the final arbitrator.
I moved on to WEZ, but that also over predicts the benefits of many things.
Another problem is either of those perspectives inevitably lead to ever larger cartridges and slicker bullets for ELR, and those methods have been shown to have limits. Cartridges have stabilized around the 375 CT and 416 Barrett. The preferred bullet is the CE Lazer, even though there are slicker offerings.
I use a cartridges overbore ratio as the starting point. It's the ratio of the case volume in grains of water to the bore ratio. It's also an imperfect metric to completely design your project with, but it's a broader perspective than drop and drift. It's closely tied to barrel life and the ability to shoot strings. If you assume a custom reamer that puts the same class of bullet for each caliber at the same position in the neck, the performance for a given overbore ratio for different calibers is similar. If there is a suitable bullet, there is a trend that favors the larger caliber. If there is a jump in bullet technology, a smaller caliber might offer more performance at the same overbore ratio.
I've either tested the cartridges in red, or watched them tested on our range. Yellow backgrounds are barrels that were tested until they were done. The parts for the 300 Lapua are here, but it's waiting for the barrel on another action to die. Barrel life isn't a linear scale on this chart, as you go lower, they die harder deaths faster than a straight line suggests.
Other things you can get from this perspective are an estimate of the QL scaling factor and powder to start testing with. You can use the scaling factor to balance the velocity and pressure estimates with your chrono and case measurements. I use 0.45 for 300wm and 338L, 0.4 for 338LI or 300 Norma, 0.35 for the 33XC and 0.3 for the 7/338LI. As far as powders, 6.5cm to 6xc work well with H4350, 7/300wsm is H4831, H1000 for 338L and 300wm, Retumbo for the 300 Norma and 338LI, H50bmg by the time we're to the 33xc.
It gives an interesting perspective on the 33 and 37xc. Tubb dropped the 37xc into the 338 Lapua range, and the 33xc with the 416 Barrett.
What does it take to shoot a mile? The wheels are falling off a 6.5cm, but it's entertaining to do. I watched a guy that knew what he was doing go 3/10 on a 20x30 plate at 2050 yards in afternoon winds without sighters. A mile is pretty easy with a long barreled 7/300wsm. You take a good guess about how well the cartidge you're thinking about using will do if you know its case capacity.
How much does increasing the overbore ratio and cashing out barrel life actually buy? 3" of barrel will just about cover the difference between a 338L and 338LI. 37XCs and 338 Lapuas continue to do well in SW ULR matches. No amount of overbore will cover factory ammo velocity spreads.
I moved on to WEZ, but that also over predicts the benefits of many things.
Another problem is either of those perspectives inevitably lead to ever larger cartridges and slicker bullets for ELR, and those methods have been shown to have limits. Cartridges have stabilized around the 375 CT and 416 Barrett. The preferred bullet is the CE Lazer, even though there are slicker offerings.
I use a cartridges overbore ratio as the starting point. It's the ratio of the case volume in grains of water to the bore ratio. It's also an imperfect metric to completely design your project with, but it's a broader perspective than drop and drift. It's closely tied to barrel life and the ability to shoot strings. If you assume a custom reamer that puts the same class of bullet for each caliber at the same position in the neck, the performance for a given overbore ratio for different calibers is similar. If there is a suitable bullet, there is a trend that favors the larger caliber. If there is a jump in bullet technology, a smaller caliber might offer more performance at the same overbore ratio.
I've either tested the cartridges in red, or watched them tested on our range. Yellow backgrounds are barrels that were tested until they were done. The parts for the 300 Lapua are here, but it's waiting for the barrel on another action to die. Barrel life isn't a linear scale on this chart, as you go lower, they die harder deaths faster than a straight line suggests.
Other things you can get from this perspective are an estimate of the QL scaling factor and powder to start testing with. You can use the scaling factor to balance the velocity and pressure estimates with your chrono and case measurements. I use 0.45 for 300wm and 338L, 0.4 for 338LI or 300 Norma, 0.35 for the 33XC and 0.3 for the 7/338LI. As far as powders, 6.5cm to 6xc work well with H4350, 7/300wsm is H4831, H1000 for 338L and 300wm, Retumbo for the 300 Norma and 338LI, H50bmg by the time we're to the 33xc.
It gives an interesting perspective on the 33 and 37xc. Tubb dropped the 37xc into the 338 Lapua range, and the 33xc with the 416 Barrett.
What does it take to shoot a mile? The wheels are falling off a 6.5cm, but it's entertaining to do. I watched a guy that knew what he was doing go 3/10 on a 20x30 plate at 2050 yards in afternoon winds without sighters. A mile is pretty easy with a long barreled 7/300wsm. You take a good guess about how well the cartidge you're thinking about using will do if you know its case capacity.
How much does increasing the overbore ratio and cashing out barrel life actually buy? 3" of barrel will just about cover the difference between a 338L and 338LI. 37XCs and 338 Lapuas continue to do well in SW ULR matches. No amount of overbore will cover factory ammo velocity spreads.
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