Home Forums Hunting & Shooting Long Range Hunting Determining a load's maximum range

I'm wondering how long range shooters define the maximum range a given load is good for? Is it the range where velocity drops to near Mach 1, or is there some other criteria?

the Mach 1 thing is a general rule of thumb, but sometimes you can go below mach 1 and still get pretty decent accuracy. a few years ago MontanaMarine here took his .308 to 1800 yards with very good results.

I accept that some loads on some days can transition to subsonic flight while retaining good accuracy. However, given the range to a target in advance, would you select a load that goes subsonic somewhere before impact, or would you stay above Mach 1? If you want to stay above Mach 1, how much of a cushion above Mach 1 is prudent?

Mach 1.2 is what German Salazar like to maintain for optimum accuracy. He's a very accomplished shooter.

If you go to the JBM trajectory calculator, it gives Mach values in the outputs.

http://www.jbmballistics.com/ballistics/calculators/calculators.shtml

Mach 1.2 is about 1,340 f/s under standard conditions per the JBM calculator. It seems then that if I'm selecting a load for long range shooting I need to find a caliber and bullet that gets me to the range I want with at least 1,340 f/s of velocity remaining.

Another consideration is the minimum terminal velocity at which your chosen bullet will still expand. If not, then the choice of bullet is immaterial other than for accuracy.

That's a good point. Just as an example, for a 300 Win Short Mag about the best flying "hunting" bullet I can find is the 150 grain SBT GameKing with a G1 BC of 0.558. A muzzle velocity of 3,300 f/s is reasonable in this caliber for a 150 grain bullet. From an accuracy standpoint it doesn't drop below Mach 1.2 until 1,375 yards, but it's down to 1,020 foot-pounds of energy by 1,200 yards where the velocity is still 1,515 f/s.

At least in this caliber it seems that good terminal ballistics sets the maximum range for hunting medium size game. Is that what others find, that the ethics of getting a clean kill on game is usually the limiting factor on range versus the potential for accuracy alone?

Per Sierra, that bullet only has a BC of .380 to .360, depending on velocity.

Sorry, it's the 200 grain bullet catalog #2165. All the velocity and energy information I gave before was correct, I just reported the wrong weight, but the MV might be beyond the 300 Win SM for a 200 grain bullet.

The 0.558 BC is the equal TOF to 1500 yards conversion of Sierra's multiple BC values (Ken Oehler's idea from the July 2007 issue of Shooting Times). Making the same conversion to G7 results in a BC of 0.282, which matches the drop of the 0.558 G1 BC to within 1% out to 1,500 yards. Strange, I thought there was supposed to be a big difference between G1 vs. G7 predicted trajectories.

OK, that sounds right.

I have some of the Sierra 200gr SPBT on the shelf here. Very accurate in my 308 Win. They do fly well too.

This is what I use as a general rule, give or take around 200 fps. Most bullet makers seem to have a floor of about 1800 fps. Not sure if that is around Mach 1.2 or not, but I would think it is. I do not pay much (any) attention the energy numbers, as in a real world, they mean very little, if anything at all to me.
Worry about the wind, everything else can be taken care of.

R.

Under standard temp and pressure, the speed of sound is 340.3 m/s[3] (1225 km/h, or 761.2 mph, or 661.5 knots, or 1116 ft/s) in the Earth's atmosphere

Mach 1.2 is about 1,340 f/s under standard conditions. I agree with you about accuracy being the number one consideration and that carries over to everything concerning shooting. The quality of a gun comes down to how accurate it is under field conditions. The quality of ammunition is judged by how accurate it is in the field, not the velocity of the bullet when it punches a hole in the target. That said, hunting ethics, at least for me, requires using a proper bullet for the intended game and having sufficient energy at impact to produce a quick kill.

1340fps would be a bit slow for me, based on the 1800fps most makers specify, being used a guideline only.

What makes a proper bullet for the intended game?
And what is sufficient energy at impact?

R.

If you're target shooting the bullet only needs to make a hole in the target, but for hunting, impact is just beginning of the bullet's job.

Other than for the smallest game you want a bullet designed for hunting rather than target shooting. Bullets intended for varmint hunting are designed for rapid expansion, but for medium and larger game hunting bullets are designed to expand reliably while retaining a high percentage of their weight for deep penetration.

How much power is needed can be calculated using various equations. For example, the Matunas optimal game weight formula.

I look at the problem from the other way around, very much like dennisiaz stated, but adjusted for my purposes. DI said he wanted to use the minimum terminal velocity to make sure the bullet expands and that is an excellent parameter. If you decide 1800FPS is your minimum, you can easily compute the maximum distance for your load to have that minimum velocity and you have your answer.

My parameters are that I want my bullet to be comfortably above Mach 1.25 at the target, the higher the better. The reason I aim for Mach 1.25 is is the start of the flight envelope when pressure on the bullet (or airplane, where I got this from) builds up rapidly as the shockwave catches up to and starts moving forward of the bullet. This reaches a maximum right at Mach 1 and then drops off rapidly below Mach 0.95. This is why you have airliners that fly at high subsonic speed but still below Mach .95. With computer control (fly by wire) punching through Mach 1 is no longer the event it was in the past, but bullets do not have on-board computer controls.

If your bullet does not get blown off course or set tumbling by the transonic passage (and very few bullets tumble) the subsonic portion of the trajectory will be very stable and you can get good accuracy. The last thing I want is to be in the Mach .95 to 1.25 envelope at the target.

So my goal is to find an accuracy node that will provide for a target velocity above Mach 1.25 (or 1.2 for general purposes) to keep my bullet from that transonic pressure area since the shock wave is left behind. Since Mach number is affected solely by temperature and I shoot most often when it can get quite hot, I try to give myself some margin. Then again, when the air is hot and humid bullets fly faster due to less air resistance so achieving a higher velocity is easier.

I used JBM to calculate the required MV for my parameters and my current .308 match load is Mach 1.4 at the 1000 yard target in 90 degree weather and 70% humidity. I suspect in July and August it�s even higher when we have 100% humidity.

So pick your desired parameter and then compute from there.

Beyond terminal ballistics, it seems the consensus is that the practical maximum range is where a given bullet drops below Mach 1.2 (about 1,340 at 59F), although some prefer Mach 1.25 or even Mach 1.6 as the low limit.

That's interesting, because while the magnitude of drag depends a great deal on the shape of a bullet, the drag profile is relatively insensitive to shape above Mach 1.2. What that means is that the G1 ballistic coefficient can accurately predict the flight of even VLD bullets in the Mach 3.5 to 1.2 velocity range, which is what it seems most long range shooters stick to.

I do things a little backwards too. Although all the charts and data look good on paper, I let the bullet tell me what it is doing. We all know that a lot of deer/elk are killed with cartridges that have 500-700 foot lbs. of energy (.30-30's, .44 mags, .223's .22's etc.) It isn't the energy that kills the critter, it is the bullet puncturing the vitals. It doesn't take much energy to do that. ON that note, I look at when the bullet starts to perform "strange" (accuracy drops off, steel target splash isn't happening, no noticeable on target impact etc.).

For instance, I shoot a .22-250 loaded with 75 grain Amaxs. It shoots great at 800 yards, just okay at 900, and crappy at 1,000. At 1,000 yards, the bullet is WAY below subsonic and becomes unstable and sometimes hits the target sideways. I don't even know if the bullet is still spinning So for this rifle, 800 is about the max I can stretch it to and actually kill/hit chucks and rodents. Flinch

Interesting, I was able to put 75gr A-max on the target at 1000 yards in summertime out of 24 inch AR-15 in .223. Winter time (such as it is in Texas,) the bullet would go in subsonic but still stable. What MV are you getting?

FTR Shooter,

Where in Texas are you? I spent the first 40 years of my life in Texas.