@kincses-zsolt @howdoiknowthisinfo
Had a talk with AI about my favourite cartridge from that spreadsheet. First I got data from a ballistic calculator then I just asked ChatGPT what would the crack-thump time be from a mic 155 yards away. @greg_n Notice the numbers from that 75 grains cartridge… About the 7 ft distance, I plotted a line from Crooks-Comperatore and beyond… then got the distance from Trump’s trajectory to that trajectory (image below). There’s also 70 grains version and another 77 that are great candidates also.
Link for the ballistic data - 75 grains
Link for the ballistic data - 62 grains
Summary of the conversation:
Crack-Thump Time Differences by Bullet and Distance
Hornady 75 grain BTHP T2 TAP Precision:
- 0 feet (direct at mic): 223 milliseconds
- 2 feet from mic: 221 milliseconds
- 7 feet from mic: 217 milliseconds
Hornady 62 grain TAP Barrier:
- 0 feet (direct at mic): 233 milliseconds
- 2 feet from mic: 231 milliseconds
- 7 feet from mic: 227 milliseconds
Each calculation takes into account the bullet’s speed at 155 yards and the respective delay caused by the sound traveling different distances to the microphone.
Below only the relevant parts, for brevity…
@bigtim @sgt-raven Do you gentlemen agree he had a 3" sight height?.
I have this set of data that I would like to ask questions about.Drag Function: G1
Ballistic Coefficient: 0.355
Bullet Weight: 75 gr
Initial Velocity: 2752 fps
Sight Height : 3 in
Shooting Angle: 0° Wind Speed: 9 mph
Wind Angle: 90°
Zero Range: 100 yd
Chart Range: 500 yd
Maximum Range: 5036 yd
Step Size: 5 yd
** Corrected For Atmosphere**
Adjusted BC: 0.38
Altitude: 0 ft
Barometric Pressure: 29.92 Hg
Temperature: 93° F
Relative Humidity: 50%
Speed of Sound: 1152 fps
Range Elevation Elevation Elevation Windage Windage Windage Time Energy Vel[x+y]
(yd) (in) (MOA) (MIL) (in) (MOA) (MIL) (s) (ft.lbf) (ft/s)
0 -3.00 0.00 0.00 0.03 0.00 0.00 0.00 1261 2752
this is the line for 155 yards - 155 -0.65 0.40 0.12 1.98 1.22 0.35 0.18 954 2393. It gives 0.18 seconds of Time. This is the time from the muzzle to the trajectory’s point at 155 yards, considering the zero sighted for the optic on the rifle.
Ok. considering this info, and that at the 155 yards distance there is a microphone recording ambient sound, and that we hear a crack-thump of the rifle being fired, how much distance would there be between the crack and the thump, in seconds (or hundreths or milliseconds). Please consider 2 alternate answers, one considering that the bullet passes 2 feet away from the microphone, and the other answer, as you choose best, with or without the mic-bullet distance at 155 yards.
### Assumptions:
** Rifle is 155 yards (465 feet) away from the microphone.*
** Speed of sound is 1152 fps.*
** Bullet speed at 155 yards is 2393 fps.*
** We are calculating the time delay based on two bullet-microphone distances: 2 feet and direct without distance consideration.*
Case 1: Bullet passing 2 feet from the microphone
- Time for the bullet to reach 155 yards: Already given as 0.18 seconds.
- Crack (bullet shockwave): The crack occurs almost instantaneously when the bullet passes 2 feet from the microphone, but sound still takes a tiny bit of time to cover the 2-foot distance. This time is:Timecrack=2 feet1152 fps≈0.00174 seconds(≈1.74 milliseconds).\text{Time}_{\text{crack}} = \frac{2 \text{ feet}}{1152 \text{ fps}} \approx 0.00174 \text{ seconds} (\approx 1.74 \text{ milliseconds}).Timecrack=1152 fps2 feet≈0.00174 seconds(≈1.74 milliseconds).
- Thump (rifle report): The time for the rifle report (thump) to reach the microphone is the distance from the rifle (465 feet) divided by the speed of sound (1152 fps):Timethump=465 feet1152 fps≈0.403 seconds.\text{Time}_{\text{thump}} = \frac{465 \text{ feet}}{1152 \text{ fps}} \approx 0.403 \text{ seconds}.Timethump=1152 fps465 feet≈0.403 seconds.
- **Total time difference (crack-thump):**Timecrack-thump=Timethump−(Timebullet travel+Timecrack)\text{Time}{\text{crack-thump}} = \text{Time}{\text{thump}} - (\text{Time}{\text{bullet travel}} + \text{Time}{\text{crack}})Timecrack-thump=Timethump−(Timebullet travel+Timecrack) Timecrack-thump=0.403−(0.18+0.00174)≈0.221 seconds (or 221 milliseconds).\text{Time}_{\text{crack-thump}} = 0.403 - (0.18 + 0.00174) \approx 0.221 \text{ seconds} \ (\text{or } 221 \text{ milliseconds}).Timecrack-thump=0.403−(0.18+0.00174)≈0.221 seconds (or 221 milliseconds).
Case 2: Ignoring the 2-foot mic distance (bullet passes directly at mic)
- Time for bullet to reach 155 yards: Still 0.18 seconds.
- Crack (bullet shockwave): No additional delay; the shockwave is heard essentially instantly at 0.18 seconds.
- Thump (rifle report): Same as before, 0.403 seconds.
- **Total time difference (crack-thump):**Timecrack-thump=0.403−0.18=0.223 seconds (or 223 milliseconds).\text{Time}_{\text{crack-thump}} = 0.403 - 0.18 = 0.223 \text{ seconds} \ (\text{or } 223 \text{ milliseconds}).Timecrack-thump=0.403−0.18=0.223 seconds (or 223 milliseconds).
Final Answer:
- Case 1 (2 feet from mic): The time difference between the crack and thump is approximately 221 milliseconds.
- Case 2 (ignoring mic distance): The time difference between the crack and thump is approximately 223 milliseconds.
What if the distance from mic to bullet was of 7 feet?
** The time difference between the crack (shockwave of the bullet passing the mic) and the thump (sound of the rifle report) would be approximately 217 milliseconds when the bullet is 7 feet away from the microphone.*