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!
I was wondering when you would chime in with that Q stock
This was the 20” setup I shot 8-9 months ago for a 3 week course.
Attachments
That's also an AT-X with a Bartlein 5R 1:10 twist barrel, is it not? Unless you retrograded it to the Walther barrel?
Thats a walther barrel I got from a guy who didn't need it anymore. I also have a 24" Bartlein 5R 1:10 twist barrel that I had spun up
Anyone know if there is there a 12 round magazine option for the AT-X / XC? I have a few of the earlier model double stack AXMC magazines which squeeze in 11 rounds which gets me close. I also tried using an AI AX AICS 10 round magazine (PN 6955) which can take an extension, but the bolt body scrapes against the magazine's single stack feed lips.
Ya I saw those. I'm using 6.5 CM and 25x47 Lapua. The OAL is too long in both of those I believe
Laughs in 14-round mag.
The fact that prs came up with 12+ round mags just to circumvent doing a mag change is comical... Seriously just load up a drum and just don't reload the whole match and it will probably take that 30lb 6gt to 35..... bush league
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I just got two of their AXMC/AXSR mag holders. What a great design and build...top quality, for sure. Easy to use, and they work perfectly
It's not just PRS. When I shoot AR tactical matches or certain divisions of USPSA I will use 40rd Magpul mags or big stick 2011 mags. It's just a competition. It's not combat.
Congrats...welcome to the most exclusive club...LH AI Owners
Right. At the geiselle gas gun matches I use 40s for my ar and 33 stendos for my Glock.It's not just PRS. When I shoot AR tactical matches or certain divisions of USPSA I will use 40rd Magpul mags or big stick 2011 mags. It's just a competition. It's not combat.
I do well
#accuracythroughvolume
I have used these for general shooting. I'm not all that impressed with their performance.
I shot them out to 600 at my local range and 5 shot groups opened up past 400 yards compared to FGMM or TRU 168 grain cartridges.
Norma used to be cheaper than FGMM, which made them a good deal. The difference is a lot closer now. I'd rather pay a little more and be assured of better performance
In fairness to HKSniper guy, AB does teach that the transonic window where percussion starts is a velocity range that equates to a couple hundred yards prior to the exact velocity of subsonic.
So it's a pretty reasonable analysis on his part. I'm guessing that's why transonic and subsonic are two different words. But I'm open to different sources and not just accepting everything I hear as gospel. Just out of pure curiosity, what is your source that shows transonic range and the exact range of entry to subsonic speed to be the same point velocity?Has anyone tried this ammo out of their AI’s?
Makes more sense for training and positional work spending less than a buck per round.
www.theamericanmarksman.com
Makes more sense for training and positional work spending less than a buck per round.
Bullets 1st .308 WIN 175 gr Sierra MatchKing HPBT - 400 ct.
www.theamericanmarksman.com
Transonic begins at 1350-1320fps depending on atmospherics. A kestrel will show clearly when transonic begins, and why you see (*) before each distance when looking at the Range Card.In fairness to HKSniper guy, AB does teach that the transonic window where percussion starts is a velocity range that equates to a couple hundred yards prior to the exact velocity of subsonic.
And every round will have a different range of distance. One round it could be 100 yards of distance. Another, 200 yards of distance. All depends on the velocity and BC of the round + atmospherics. It's physics: Ballistics are different in the Supersonic, Transonic and Subsonic ranges.
Ya, I was taught the manual version of truing DSF before they were programmed into AB in the 5700 elites. We just did it manually and had stepped BCs for different velocities. Understanding the transonic window, prior to subsonic, is a function of truing into subsonic. If you use the Cal DSF in AB but also disagree with what AB says about transonic windows you're kinda being a dumbass. I'm not going to hitch my wagon to AB and say that everything their teaching is irrefutable fact. I've been taught all kinds of shit that ended up being proven untrue over the last 22 years doing this professionally. The old high angle formula, the old thought effect of spindrift that ended being proven to be a Leupold M3A and M3LR mechanical effect, and more. I'm still waiting for someone to disprove AJ. I just turn winds off and don't even bother factoring into data. But maybe I'm just being lazy. That's why I asked what MK20's source was. I'm open to learning despite whatever expert status and experience I like to think I have. If he comes back with data driven explanation from a reputable source then I'd be interested. If it's just I shoot a lot and have been around a while then I'll chalk it up to an old guy with an online presence to defend. There's a lot of us who shoot a lot and have been around for a while. That's not going to be convincing.
ETA: meant CAL DSF
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I'm a self proclaimed mag change expert. But I'd rather not do it during a PRS stage if I can help it
The transonic region is between Mach 0.8 and 1.2 but how it affects an object really depends on the specific aerodynamics of that object. At the most basic level "transonic" really means that you're in a region of speed where there may be some subsonic flow over your object and there may be some sonic (Mn=1.0) flow.
Conjecture time: understanding the weird aerodynamics that occur in this region really matters for aircraft or things trying to accelerate through the speed of sound. Since a rifle bullet is sledgehammered through the sound barrier in the barrel we really don't care about that but we do care about the deceleration side downrange. I remember reading that 168gn Sierras hit a wall at distance as when they went transonic the shockwaves would collapse and destabilize the bullet due to its boattail angle. Whether or not this is true got me thinking about deceleration through the sound barrier and I would say that first, rifle bullets are shaped very consistently so your transonic region will be a lot tighter than 0.8Mn to 1.2Mn. Second, the destabilizing effects will only be shown by either a localized subsonic flow or total collapse of the shockwave meaning it'll be closer to the slow end of the transonic region. Third, the bullet is supersonic until that happens and once shockwaves start collapsing the drag will increase fast and the bullet will quickly be subsonic and out of that region.
Having said all that I've never read any true ballistics books, this is just me guessing at some things based on my understanding from being around some aerospace engineers in college and trying to make the transonic stuff a little easier to understand. Hopefully I labeled my guessing areas well enough and have given sufficient disclaimers to say if you actually listen to me that's on you.
Conjecture time: understanding the weird aerodynamics that occur in this region really matters for aircraft or things trying to accelerate through the speed of sound. Since a rifle bullet is sledgehammered through the sound barrier in the barrel we really don't care about that but we do care about the deceleration side downrange. I remember reading that 168gn Sierras hit a wall at distance as when they went transonic the shockwaves would collapse and destabilize the bullet due to its boattail angle. Whether or not this is true got me thinking about deceleration through the sound barrier and I would say that first, rifle bullets are shaped very consistently so your transonic region will be a lot tighter than 0.8Mn to 1.2Mn. Second, the destabilizing effects will only be shown by either a localized subsonic flow or total collapse of the shockwave meaning it'll be closer to the slow end of the transonic region. Third, the bullet is supersonic until that happens and once shockwaves start collapsing the drag will increase fast and the bullet will quickly be subsonic and out of that region.
Having said all that I've never read any true ballistics books, this is just me guessing at some things based on my understanding from being around some aerospace engineers in college and trying to make the transonic stuff a little easier to understand. Hopefully I labeled my guessing areas well enough and have given sufficient disclaimers to say if you actually listen to me that's on you.
I couldn't agree more. But I'm also not experienced enough to know how to build a Custom Drag Model besides sitting there and shooting rounds at a target within the transonic window. So for those who don't know -- and myself now researching how best to build CDMs -- I'm leaving the info below here. So it sparks an interesting debate: use a round that is supersonic at 1000 yards but doesn't group as tight, or use a round that groups much tighter, but needs a CDM to hit 1000 yards on target consistently?
* * *
Custom Drag Models (CDMs) are used to model the flight path of bullets, and are particularly important for accurately predicting trajectories beyond the transonic range. The transonic range is when a bullet slows below Mach 1.2, or around 1340 feet per second (fps).
Here's some more information about CDMs and the transonic range:
CDM accuracy
CDMs can provide highly accurate predictions, with one example showing a match within +/- 9 inches for a bullet traveling up to 1323 yards.
CDM generation
CDMs are generated using Doppler Radar to directly measure a bullet's drag profile.
CDM availability
CDMs are available for all bullets in the Applied Ballistics software ecosystem.
CDM benefits
CDMs eliminate the variation between a bullet's actual drag and the standard model being used.
Transonic range challenges
The transonic range is difficult to predict because of the mismatch between the standard G1/G7 drag curves and the bullet's actual CDM.
Transonic range effects
The transonic range can cause bullets to yaw and destabilize. Short, flat base bullets are less affected by the transonic range than
long, thin bullets.
Regarding the factory AI AT 308 barrels with the UK proof markings, do they speed up with use?
I got 2,550 with my 24” and 175 FGMM for the first ten rounds fired.
-Stan
I got 2,550 with my 24” and 175 FGMM for the first ten rounds fired.
-Stan
Related to all this is Litz's new theory about .22LR match ammo that starts just over supersonic and slows to subsonic. He articulates some effects. If you believe him, then it further supports that transonic is a range prior to sub. If you're not a believer of Team AB and think they, like other scientists, may change their theories in the future as they learn more, I totally get that. But id also like to see the other data.
I don't think CDMs are really that necessary. Accuracy and precision are. With the accuracy of today's chrono's I think we're better off truing BC than velocity like we used to do in 2006. Guys that experiment with Oehler 88's are finding that BC varies from bullet to bullet and from barrel to barrel. So I would find load that starts accurate and true a G7 out to just prior to the trans window, based on a Garmin Zero speed. Then CAL DSF in trans prior to sub and again post subsonic by shooting and gathering data(like MK20 suggests) and blammo, you have a CDM for your gun.
What are your thoughts on 4DOF since it uses muzzle velocity as a known parameter? Sounds like you might like that better than the AB method...
I'm not going to pretend to be a guru on everything; I don't have any real experience with Hornady 4DOF.
Bro, we're trying to nerd out over here on some super serious high brow theoretical ballistic shit; super important high end stuff! ....and you're butting in with some mouth-breathing day 1 shit like, "Do barrels speed up?".
You could just shoot 6.5 and use Strelok like the smart people do
Instead of pondering Sonics and other nonsensical bs
Instead of pondering Sonics and other nonsensical bs
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