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:

​

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

​

​

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