Spindrift
Well-Known Member
I think many of you may have this mould lying around. The stated purpose of this design, is as a subsonic bullet for the .300 BLK, or other fast-twists, for that matter.
Another potential use, could be as a long- range target bullet, owing to the phenomenal ballistic coefficient (BC) of this bullet. Lee claim it is 0.688. That’s a bit better than the Hornady .308 cal 225grs HPBT- bullet. Seriously good BC, really!
Some measurements of my bullets, as cast.
Base of the nose: .298
Front driving band: .304
Microbands: .310
Rear driving band: .3105
Alloy is a plumbous mystery alloy that harden to about BHN 14-15.
So, the typical under-sized nose. But if we consider this in the context of «core-mould for PC», and add 0.002in to all diameters- things are looking better! At least for a throat with little wear. I happen to have a Rem 700 with a virtually new Schultz & Larsen 30-06 barrel (good stuff).
Now, I’ll do a little comparison of two hypothetical cast bullet loads, to show you why this bullet gets interesting at long range. If you have no interest in calculations, skip to the next post (that’s where the shooting starts!).
In this exercise, we’re assuming we cast geometrically perfect bullets, where theoretical group size is strictly proportional to shooting distance (accuracy in MOA is the same at all ranges).
Our hypothetical load #1 is with the XCB- bullet. In fact, it’s a very good load that propels our bullet at 2450 fps with 1MOA accuracy.
Listed BC of the XCB- bullet, is 0.287
Load #2 is with the Lee- bullet, propelled at 1900fps with 1,5MOA accuracy.
Listed BC of the Lee 309-230 is 0.688
So, the Lee is slower from the muzzle, and has inferior accuracy. Which loads would give us the best chance of hitting a steel plate at, say, 550 yards?
First, some basic calculations. The XCB will shed speed much faster than the Lee. Actually, at 340 yards velocity will be the same. The XCB remains supersonic to 580y, while the Lee keeps supersonic to 1040y (!).
The challenge with long-range, is to judge wind. The problem is not that it’s difficult; it’s actually impossible. Because you’re compensating for wind that hasn’t happened yet. And you’re calling the wind based on it’s effect on vegetation etc on the ground, while in the non-range setting you often shoot through higher air-streams that are typically stronger (across a valley, for instance).
Therefore, a high-BC bullet is invaluable; it reduces the consequences of our erroneous wind corrections.
Let’s see what happens with our two loads at 550y, if the shooter underestimates the wind by 1m/s (2,2mph). Which is still a pretty good call.
At 550y, our fantastic XCB- load has a group size of 5,5in. But the wind not accounted for, will drift the bullet about 12 inches.
Our Lee load, #2, will have a theoretical group size of 8,25 in. The wind not accounted for, will drift the bullet 5,5 inches.
My guess is, the Lee- load will hot the plate more often, despite starting at a lower velocity, and being slightly less accurate in this example.
Another potential use, could be as a long- range target bullet, owing to the phenomenal ballistic coefficient (BC) of this bullet. Lee claim it is 0.688. That’s a bit better than the Hornady .308 cal 225grs HPBT- bullet. Seriously good BC, really!
Some measurements of my bullets, as cast.
Base of the nose: .298
Front driving band: .304
Microbands: .310
Rear driving band: .3105
Alloy is a plumbous mystery alloy that harden to about BHN 14-15.
So, the typical under-sized nose. But if we consider this in the context of «core-mould for PC», and add 0.002in to all diameters- things are looking better! At least for a throat with little wear. I happen to have a Rem 700 with a virtually new Schultz & Larsen 30-06 barrel (good stuff).
Now, I’ll do a little comparison of two hypothetical cast bullet loads, to show you why this bullet gets interesting at long range. If you have no interest in calculations, skip to the next post (that’s where the shooting starts!).
In this exercise, we’re assuming we cast geometrically perfect bullets, where theoretical group size is strictly proportional to shooting distance (accuracy in MOA is the same at all ranges).
Our hypothetical load #1 is with the XCB- bullet. In fact, it’s a very good load that propels our bullet at 2450 fps with 1MOA accuracy.
Listed BC of the XCB- bullet, is 0.287
Load #2 is with the Lee- bullet, propelled at 1900fps with 1,5MOA accuracy.
Listed BC of the Lee 309-230 is 0.688
So, the Lee is slower from the muzzle, and has inferior accuracy. Which loads would give us the best chance of hitting a steel plate at, say, 550 yards?
First, some basic calculations. The XCB will shed speed much faster than the Lee. Actually, at 340 yards velocity will be the same. The XCB remains supersonic to 580y, while the Lee keeps supersonic to 1040y (!).
The challenge with long-range, is to judge wind. The problem is not that it’s difficult; it’s actually impossible. Because you’re compensating for wind that hasn’t happened yet. And you’re calling the wind based on it’s effect on vegetation etc on the ground, while in the non-range setting you often shoot through higher air-streams that are typically stronger (across a valley, for instance).
Therefore, a high-BC bullet is invaluable; it reduces the consequences of our erroneous wind corrections.
Let’s see what happens with our two loads at 550y, if the shooter underestimates the wind by 1m/s (2,2mph). Which is still a pretty good call.
At 550y, our fantastic XCB- load has a group size of 5,5in. But the wind not accounted for, will drift the bullet about 12 inches.
Our Lee load, #2, will have a theoretical group size of 8,25 in. The wind not accounted for, will drift the bullet 5,5 inches.
My guess is, the Lee- load will hot the plate more often, despite starting at a lower velocity, and being slightly less accurate in this example.
