I think he is having a "not actually shooting his rifle out to distance and merely looking at numbers" issue.
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This disease is similar to Borescope Hypochondria — Hypothetical DOPE Mania.
Both conditions will be in the next edition of the DSM.
-Stan
Uhh are you saying if your bullets went wonky at 1100, they magically moved back on target at 1200?
My first AI. Waiting on a proof pale brown 6.5 barrel to ship out and hopefully hunt down a factory pale brown forend grip to replace the RRS. I’ve got a 6.5 TBAC Ultra 7 in route as well. Looking forward to using this thing.
There's nothing magic about this. Having accurate DOPE within the transonic window is highly inconsistent; it is a known and well documented issue. Having dope before -- or after -- the round is transonic, offers a more consistent window. I am not using the words "accurate" or "precise." I am very specifically using the word "consistent" in terms of bullet stability and having DOPE for that round.
C'mon guys, its like you guys have never shot in the transonic or subsonic windows before. This isn't rocket science.
Um, I'm pretty sure you don't understand how this works. Angular deviation seen as dispersion is real, and permanent once it happens in flight.
The snide remark is noted... if I had a 1000 yard range, I'd be testing it. But frankly, I don't and so I need to do the math and run numbers. Its that simple.
Transonic Ballistics Effects Explained by Bryan Litz
What happens when the bullet slows to transonic speed, i.e. when the bullet slows to about 1340 feet per second? It is getting close to the speed of sound, close to the sound barrier. That is a bad place to fly for anything. In particular, for bullets that are spin-stabilized, what the sound barrier does to a bullet (as it flies near Mach 1) is that it has a de-stabilizing effect. The center of pressure moves forward, and the over-turning moment on the bullet gets greater. You must then ask: “Is your bullet going to have enough gyroscopic stability to overcome the increasing dynamic instability that’s experienced at transonic speed?”
Some bullets do this better than others. Typically bullets that are shorter and have shallow boat-tail angles will track better through the transonic range. On the contrary, bullets that are longer… can experience a greater range of pitching and yawing in the transonic range that will depress their ballistic coefficients at that speed to greater or lesser extents depending on the exact conditions of the day. That makes it very hard to predict your trajectory for bullets like that through that speed range.
When you look at transonic effects on stability, you’re looking at reasons to maybe have a super-fast twist rate to stabilize your bullets, because you’re actually getting better performance — you’re getting less drag and more BC from your bullets if they are spinning with a more rigid axis through the transonic flight range because they’ll be experiencing less pitching and yawing in their flight.
The short version: I'm trying to find a round that either can push through the transonic window effectively -- as I have in the past when I had access to 1200 yards -- or, focus on using a round that is effective out to 1000 yards and still supersonic. While my MR762s could do this with the 1:11 twist barrel using Hornady TAP ELD AR 168gr, I am not as confident with a 1:12 twist barrel using Federal GMM SMK 175gr.
And since I cannot test this myself, I was fairly confident that there were SH community members with many years of AW308 experience who could save me the money and trouble. Some of you have answered my question, and I think testing just two factory rounds out as far as I can go is worth it: FGMM SMK 175gr due to it having the greatest stability factor of all the rounds while being heavy enough, and Hornady TAP ELD Precision 168gr due to it having the greatest BC and fastest velocity.
So I'm going to leave this to rest until I can afford to go test these, and will try to find a 1000+ yard range to do so. When I have the data, I will report back.
In the mean time, I'd still like to hear from specifically Arctic Warfare owners on your experiences over the years.
Speaking of being a nerd....
For those wanting to shoot NRL Hunter with your AXSR. I found a way without any excessive purchases or the use of a 9-axis CNC.
For the barrel I estimated the weight for a 20" CF 6.5 CM, using my Proof CF 24" 6.5 PRC (56.1oz) and my Proof CF 18.5" .308 Win barrel (48.3oz). I figured I would try CarbonSix barrels using their Sendero profile.
There's 5.1oz tied up in small parts in the stock alone (extension plate: 1.0oz, QR latches: 0.6oz each, washer: 0.3oz, stock folder latch parts: 1.2oz, and the QD receivers: 1.4oz). The standard grip is 4oz, which can be replaced with an MKM Shadow Crossover Grip (2.3oz).
I am tempted to ask MKM to make a fixed stock adapter similar to the ATX to drop around 3oz potentially.
The other option is to drop the bipods and run a suppressor, and rely on the tripod or shoot from a pack.
For those wanting to shoot NRL Hunter with your AXSR. I found a way without any excessive purchases or the use of a 9-axis CNC.
For the barrel I estimated the weight for a 20" CF 6.5 CM, using my Proof CF 24" 6.5 PRC (56.1oz) and my Proof CF 18.5" .308 Win barrel (48.3oz). I figured I would try CarbonSix barrels using their Sendero profile.
There's 5.1oz tied up in small parts in the stock alone (extension plate: 1.0oz, QR latches: 0.6oz each, washer: 0.3oz, stock folder latch parts: 1.2oz, and the QD receivers: 1.4oz). The standard grip is 4oz, which can be replaced with an MKM Shadow Crossover Grip (2.3oz).
I am tempted to ask MKM to make a fixed stock adapter similar to the ATX to drop around 3oz potentially.
The other option is to drop the bipods and run a suppressor, and rely on the tripod or shoot from a pack.
I’ve put about 2500 rounds of 175gr through a specific 20” 1:12 twist LW barrel.
My experience with it showed it did not group the best at 100m but actually tightened up at moderate distances, almost as if initially the bullet had gone to sleep.
Looking at some of your groups in an earlier post it seems you are doing the same thing by fighting that twist rate.
Especially out past 1000 yards with your bullet selection.
The one round I found to do really well was the 176gr A-TIP, the BC bump and design of the projectile lended well at 1000+ yards.
I do see what you’re trying to do and you’re definitely pushing the limits of your system!
Look man…I’m just sayin the dremel is a solid option. Could probably also flute my barrel with it too.
Now we're talking. Input!I’ve put about 2500 rounds of 175gr through a specific 20” 1:12 twist LW barrel.
My experience with it showed it did not group the best at 100m but actually tightened up at moderate distances, almost as if initially the bullet had gone to sleep.
Looking at some of your groups in an earlier post it seems you are doing the same thing by fighting that twist rate.
Especially out past 1000 yards with your bullet selection.
The one round I found to do really well was the 176gr A-TIP, the BC bump and design of the projectile lended well at 1000+ yards.
I do see what you’re trying to do and you’re definitely pushing the limits of your system!
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