Is bullet still stable/accurate after it goes subsonic?

[MMH]

Is a bullet still stable/accurate after it goes subsonic?

I know that my precision AR is a tack driver out to 800 yards, but falls off the face of a cliff at 900. Thinking that is because at 800 yards bullet is going transonic. So thinking about various cartridges, what is the max range? I ran through the following calcs:

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Cartridge	MV	Bullet	Yards	FPS	mach
5.56	2850	75 BTHP	800	1173	1.07
6.5CM	2789	147 ELD-m	1500	1231	1.10
3088	2550	178 ELD-M	1000	1227	1.12
300WM	2850	225 ELD-M	1700	1203	1.10
338 Lapua	2900	285 ELD-M	1900	1173	1.07

​

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Seems like many are shooting those cartridges past the above distances I have. Also, what would the advantage (other than energy) be for a 338 over a 300WM at a mile and wouldn't you be able to take a 300WM as far as a 338 accurately?

I want to take my 6.5 CM and try shooting at a mile (the bullet will be at 1050 fps or m=.94) - will this be possible? My 300WM is only a 2 minute rifle so no point in trying to take it that far & I do not have a 338.

 

[Ronin22]

Guys shoot 6.5CM at the mile all the time around the country. I’ve witnessed guys do it myself. I shot it with 300WM no problem, but the bigger cartridge/caliber you go helps with maintained velocity down range and less resistance to wind gusts.

The type/quality of bullet will allow it to stay stable through the transition zones and beyond. Check out “Mark & Sam After Work” he shoots insane distances you can’t believe possible.

 

[MarshallDodge]

Don't forget to consider time of flight and velocity. The bullet is traveling much slower at the end of it's flight than when it left the barrel. That is where wind, etc can have a bigger effect on the where it impacts.

 

[Taylorbok]

We shoot our 375's over 2 miles. (3520 Yards) depending on DA my projectile goes through trans around 2000 yards, once it gets to target at 2 miles it's under 1000 fps

Yes they are still stable into subsonic

 

[MMH]

Thanks for the replies. Asked because only direct experience I had was with my 5.56. And I can get to 800 but anything else it falls off the cliff. Maybe its just bad through the transonic range. Don't know as I never tried shooting it at 1100 or 1200 yards.

 

[Taylorbok]

Thanks for the replies. Asked because only direct experience I had was with my 5.56. And I can get to 800 but anything else it falls off the cliff. Maybe its just bad through the transonic range. Don't know as I never tried shooting it at 1100 or 1200 yards.

Some bullets do go through trans better than others.
What do you mean by falls off a cliff? as mentioned wind will have a larger impact the slower the bullet is going.

 

[MMH]

Some bullets do go through trans better than others.
What do you mean by falls off a cliff? as mentioned wind will have a larger impact the slower the bullet is going.

What I mean is that I can make fairly reliable hits at 800 but at 900 or 1000 all over the place and way off the target. I shoot a Hornady 75 BTHP as the gun is magazine fed.

 

[Taylorbok]

What I mean is that I can make fairly reliable hits at 800 but at 900 or 1000 all over the place and way off the target. I shoot a Hornady 75 BTHP as the gun is magazine fed.

that's probably ES/SD showing up at distance and the wind pushing the bullet around more

 

[MarshallDodge]

that's probably ES/SD showing up at distance and the wind pushing the bullet around more

Agreed, as well as bullet quality and BC variance.

A friend shoots the 73 ELD in his AR for this reason. It does great when the wind is consistent.

 

[secondofangle2]

My 75 ELDM is good to 1200 yards but it starts at 2950 fps in a 7.75 twist

You’re not dealing with transonic at 1000, you’re dealing with a light bullet going slow getting beat by the wind. And the aforementioned BC variation, SD

 

[ggmanning]

I find some are. My 75 Amax, 77SMK, Berger 140 VLD's, 215 hybrids, 105 hybrids pass the barrier well and predictably in my set ups. 168 and 175 SMk's do not. 168's do fall off a cliff as in don't see them anywhere on the berm past supersonic from my 16" .308

 

[jpjulian]

The H75HPBT didn't shoot for beans out of my 7-twist 20" service rifle barrels at 600 yards. For whatever reason the S77MK was considerably better at 600.

 

[secondofangle2]

yeah, and you try to take a 55 grain to 800 yards from an AR, you may as well pick up a handful of gravel and throw it at the target

 

[Rocketmandb]

105 hybrids pass the barrier well and predictably in my set ups

I shoot those out of my 6 BRA - I've taken it to 1840 yards in light wind. I don't think that bullet cares if it's subsonic one bit.

 

[SIDS01]

I put these together to figure out what to work on next for better ELR performance.



It's the error budget for a very competetive 2 mile gun. 375CT, 2950 fps, 400gr Lazer, 15 fps ES for 20 shots, 1.5% BC spread for 20 shots, 0.5 moa. The total vertical spread is the root mean square sum of the 100 yard precision, the velocity spread, and the BC spread. I have a few AB CDM data sheets that are a little lower, but that would be an exceptional gun if that level of performance could be produced on demand every time.

The first thing that should be noticed is 100, 1000, 2000, and 2 miles have very different problems. At 100 yards, precision is all that matters. By 3000 yards, BC variation dominates the problem. Velocity spread is a bigger deal than precision by 2000 yards. My take on it is after a mile, if you're doing the things to minimize Velocity and BC spread, the precision component is pretty much taken care of as a side effect. That is, 1 moa or 0.5 moa just isn't your biggest problem at ELR distances.

If we compare the 2 mile gun to a 6.5CM loaded to the same standards, we see that yes, cartridge does matter.



On the other hand, if we plot the vertical spread against time of flight instead of distance we get this:



They're not really that different from that perspective. 2 mile training ranges are rare and generally distant. 2 mile ammo and barrel life are relatively expensive. The idea that vertical spread scales to TOF can be manipulated for selecting a gun that'll give representative 2 mile training at more accessible ranges.

That perspective also leads to the idea that going after TOF with more velocity and higher BCs is the most obvious way forward. The problem with that is you can't afford to give up a thing on Velocity or BC spread while you do it.

 

[SIDS01]

These are the error budgets for that 375 with the Velocity spread opened up to 30 fps, the BC spread to 3%, and the precision to 1.0 moa for the Intermediate shooter. The Beginner has 60 fps, 6% BC, and 1.5 moa. This is as much about the reloader as it is the shooter.



Wind is included here as well to provide another sense of scale.

Another huge problem with bum rushing the problem with velocity and BC is most ELR matches require strings of 10+ shots and the match is generally decided at the longest targets which are the last ones shot.

 

[secondofangle2]

I put these together to figure out what to work on next for better ELR performance.



It's the error budget for a very competetive 2 mile gun. 375CT, 2950 fps, 400gr Lazer, 15 fps ES for 20 shots, 1.5% BC spread for 20 shots, 0.5 moa. The total vertical spread is the root mean square sum of the 100 yard precision, the velocity spread, and the BC spread. I have a few AB CDM data sheets that are a little lower, but that would be an exceptional gun if that level of performance could be produced on demand every time.

The first thing that should be noticed is 100, 1000, 2000, and 2 miles have very different problems. At 100 yards, precision is all that matters. By 3000 yards, BC variation dominates the problem. Velocity spread is a bigger deal than precision by 2000 yards. My take on it is after a mile, if you're doing the things to minimize Velocity and BC spread, the precision component is pretty much taken care of as a side effect. That is, 1 moa or 0.5 moa just isn't your biggest problem at ELR distances.

If we compare the 2 mile gun to a 6.5CM loaded to the same standards, we see that yes, cartridge does matter.



On the other hand, if we plot the vertical spread against time of flight instead of distance we get this:



They're not really that different from that perspective. 2 mile training ranges are rare and generally distant. 2 mile ammo and barrel life are relatively expensive. The idea that vertical spread scales to TOF can be manipulated for selecting a gun that'll give representative 2 mile training at more accessible ranges.

That perspective also leads to the idea that going after TOF with more velocity and higher BCs is the most obvious way forward. The problem with that is you can't afford to give up a thing on Velocity or BC spread while you do it.

This might be the most informative post I have ever seen on snipers hide

Who are you?

 

[secondofangle2]

And one message I take from it is that first shot hits fall apart after 2000 yards

 

[brianf]

I don’t want to be that guy..but I don’t understand why people shoot cartridges way past their expected / designed criteria.

If your shooting 2500 yards I can see purposefully shooting a cartridge that goes subsonic etc..there arent any that stay supersonic.

The amount of ammo wasted shooting a 6.5 creed trying to hit anything of “normal” size, and hoping for “regular hits”…is 10X more expensive that getting a 600$ barrel for your win mag.

Why …because a win mag with a Berger is great for 1500. Or rechamber for 400$ to a 300 prc and bang away at a mile with factory Hornady AMax.

 

[kthomas]

Depends on the projectile.

I think a lot of it has to do with Cg of the specific profile, and certain aerodynamic characteristics of the projectile.

Our resident bullet engineer @Ledzep can probably provide more details.

 

[SIDS01]

These graphs are made from range cards exported to a spreadsheet and plotted. Three cards per cartridge, a baseline, baseline - 100 fps, and baseline -10% BC. The differences are calculated for each range and scaled to 3 levels of dispersion, velocity spread, and BC variation. Extreme Spreads are taken as 4X the SD of strings with a minimum of 10 shots.

The rounds in the next chart were selected to give a large difference in BC at the same velocity. 300 grain bullets out of a 26" 338 Lapua and 140 ELDm out of a 26" 6.5CM, both at 2750 fps.



I listed the assumed dispersion, velocity spread and BC variation for each level in my earlier post. For those that don't chrono much, the Novice or Beginner level is decent commercial match ammo with an SD in the high teens. It'll take a while after buying your first reloading stuff to load at the intermediate level, high single digit velocity SDs.

This is where the division forms on whether or not 6.5CM is a suitable 1 mile cartridge. Decent 6.5CM reloads will outperform factory 338 Lapua on the vertical spread. Yes, the wind will be worse, but it doesn't take much difference in shooter skill to cover that. The 300 PRC gives 338 Lapua performance at a much lower cost, so the comparison applies there as well minus the wind penalty. If you're using a 1 mile gun as a training tool, you may not regard the increase in wind deflection as a penalty.

Next, lets compare a 338 Lapua with a 33XC. Same 300 grain bullet so no BC difference. The 33XC will be 300 fps faster at 3050 fps.



Even 300 fps of velocity won't cover the steps in ammo consistency.

The next chart compares the 33XC with the 375CT. 300 gr ATips at 3050 with the 33XC, 400 gr Lazers at 2950 fps for the 375CT.



The 375 OL has the velocity spread reduced to 10 fps and BC spread to 1%. Even with very good ammo, the way forward at extreme distances is continuing to reduce the spreads.

 

[SIDS01]

This might be the most informative post I have ever seen on snipers hide

Who are you?

Thank you.

I'm nobody. Just another hobbyist who occasionally competes. I scored the first shooter point in the URSA for 5/10 on a 37" gong at 2K yards in 2015. SIDS01 is Shooter ID, Shooter #1. I get to be #1 forever because I was the first, not because I'm the best. I switched to that screen name to tease the guys that run the URSA online. They knew who it was, but it didn't look to the public like one of their shooters was trashing them. On other forums, I use my real name to keep myself civil, but I haven't switched here yet.

I'm trying to find the shortest way to explain this stuff to new shooters. The OP's question and the way it was presented made this thread seem like a good place to hang the information. 10 years ago, they were still stoning people who suggested they were shooting deep into the transonic. The OP accepted that it was happening and wanted to know how. He also brought multiple cartridges into the discussion.

 

[SIDS01]

And one message I take from it is that first shot hits fall apart after 2000 yards

It's like anything else, some do it a lot better than others. I look at it like a game of Blackjack. You can't win every hand. Some can stretch a little luck a long way, others piss away opportunities.

The first shot brings other uncertainties into the mix.

Knowing what you're up against helps. If you're shooting a group that's larger than the target, simply chasing your last miss may amplify the problem. Learning to stay up on the changes that happen between shots carries over into improving your first guesses.

 

[Ledzep]

Depends on the projectile.

I think a lot of it has to do with Cg of the specific profile, and certain aerodynamic characteristics of the projectile.

Our resident bullet engineer @Ledzep can probably provide more details.

It's been a minute since I looked at this subject. I ran a bunch of 6DoF simulations but the simulations are always subject to the input/boundary conditions vs. reality so it can be difficult to verify if any of it is real trends or just junk data. I think years ago Jayden did a bunch of testing with "notorious" bullets and found them not to be as notoriously bad as some publications had suggested.

I would say as a general statement it will depend on the bullet for sure, the day for sure (wind/environmental conditions) and may even be a little bit variable barrel to barrel or load to load. You have a spin-stabilized projectile and you hit it with perturbations and it either recovers easily, recovers after a while, or doesn't recover. It will depend on the response (specific to that projectile in its fired down-range state) and the specific perturbance(s). Obviously the easy button is to say to keep things > Mach 1.2 to the target if at all possible.

Assuming no-wind perfect conditions, at some point they all go AoA-wild. It's usually simulated to be well past the trans-sonic speed (2000yd-5000yd for most of the stuff discussed in this thread) and I believe that is Magnus moment that eventually makes things fly off the rails. I also did a bunch of iterations of bullet design to try to cheat that and it turns out the things that decrease the destabilizing effects encountered towards the end of the trajectory are also things that increase drag considerably. The only real solution that I remember was to shoot a bigger badder bullet.

 

[Buford Boone]

It's been a minute since I looked at this subject. I ran a bunch of 6DoF simulations but the simulations are always subject to the input/boundary conditions vs. reality so it can be difficult to verify if any of it is real trends or just junk data. I think years ago Jayden did a bunch of testing with "notorious" bullets and found them not to be as notoriously bad as some publications had suggested.

I would say as a general statement it will depend on the bullet for sure, the day for sure (wind/environmental conditions) and may even be a little bit variable barrel to barrel or load to load. You have a spin-stabilized projectile and you hit it with perturbations and it either recovers easily, recovers after a while, or doesn't recover. It will depend on the response (specific to that projectile in its fired down-range state) and the specific perturbance(s). Obviously the easy button is to say to keep things > Mach 1.2 to the target if at all possible.

Assuming no-wind perfect conditions, at some point they all go AoA-wild. It's usually simulated to be well past the trans-sonic speed (2000yd-5000yd for most of the stuff discussed in this thread) and I believe that is Magnus moment that eventually makes things fly off the rails. I also did a bunch of iterations of bullet design to try to cheat that and it turns out the things that decrease the destabilizing effects encountered towards the end of the trajectory are also things that increase drag considerably. The only real solution that I remember was to shoot a bigger badder bullet.

I suspect the best way to know is to measure the drag consistency.

It would make sense to me that If the drag consistency is low in supersonic and also low in subsonic, the bullet would have been stable the whole way.

 

[TripleBull]

I find some are. My 75 Amax, 77SMK, Berger 140 VLD's, 215 hybrids, 105 hybrids pass the barrier well and predictably in my set ups. 168 and 175 SMk's do not. 168's do fall off a cliff as in don't see them anywhere on the berm past supersonic from my 16" .308

In my very limited experience, have found the "some are" to be a key. During a period of stretching a 338LM out with Lapua factory ammo, I read a post here on the Hide about the 250 grain Scenar transitioning to subsonic better than the 300 Scenar. I was skeptical, but began comparing the two. At that point, I was at 2000 yards and the 300 Scenar had been performing well. I backed up to 1000 yards and then stepped up eventually to 2400 yards. We got better performance out of the 250 Scenar - it wasn't dramatic, but it was consistent.

I did a comparison of projectiles for 308 and found the Berger 168 Hybrid and Sierra 168 FGMM to transition best of those tested. I'd think my tests only offered results specific to the rifles used as I did not vary twist rate, etc.

 

[TripleBull]

I don’t want to be that guy..but I don’t understand why people shoot cartridges way past their expected / designed criteria.

Guilty as charged, but only occasionally, so it's not a real ammo or barrel wasting activity for me. Ammo is a large part of my leisure budget, so factory ammo and reloading components add up to a sobering level. Spending my shooting time and money doing stuff I find to be fun is worth it to me. I spend so much time doing systematic work to characterize my rifles within their wheelhouse, over-range plinking is a nice diversion.