08 February 2019
Could you give an example of using time of flight and velocity lost? Do you compare it with bullet BC? My limited experience so far shows woefully low BC. I think the bullet is really wobbling.
Here's a fairly recent example; It was a test of an unopened box (20 rds) of M118SB. I shot a 10 shot test in my 14" twist .308W Palma rifle and the other 10 shots in my 12" M70 target .308 rifle. The Palma rifle has a 27" barrel and the M70 a 26" barrel. The tests occurred on the same day under the same conditions about 40 minutes apart.
The M70 gave the following data;
Muzzle velocity; 2653 fps
Down range velocity at 285 ft; 2471 fps with a velocity loss of 182 fps and a TOF of .110895 (milliseconds)
Measured BC; .517
The Palma rifle gave the following data;
Muzzle velocity; 2642 fps
Down range velocity at 285 ft; 2431 fps with a velocity loss of 211 fps and a TOF of .112519 (milliseconds)
Measured BC; .448
The data from the 12" twist M70 is very consistent with arsenal published data for M118 SB ammunition for use in a 12" twist barrel. The BC for the M118 174 gr FMJ M118 bullet is in the .485 to .500 range from a 10" twist barrel. Arsenal testing back in the '50s demonstrated the 12" twist to give the best accuracy with the 147 - 174 gr bullets in the 7.62 NATO cartridge.
What we see from the data is the 14" twist Palma rifle the TOF over the same distance was longer with a greater velocity loss resulting in a much lower BC. The reason for the different measured BCs is because the M118 bullet stabilized fully in the 12" twist. The M118 bullet was only marginally stabilized in the 14" twist rifle and therefore had more yaw,pitch and/or wobble thus it slowed down faster and since it was not as efficient moving through the air it gave a smaller BC. The higher the BC of a given bullet at a given velocity the more stable it is.
My M43 PBL came with a 100 yard cable for the down range screens so that is what I use. The TOF is measured from the muzzle screens to the down range screens which are in front of the 100 yard target. The actual distances are carefully measured and entered into the program.
The M43 PBL measures a multitude of things concerning the internal ballistics as stated including the efficiency of the load. The M43 also measured a lot of external ballistic data that is very useful. While the Labradar gives a bit more data of the external ballistics it only gives, the same as any chronograph, a small picture of the internal ballistics. A friend of mine has a Labradar and we are planning a side by side concurrent use it with the M43. If it provides additional useful data I will probably get one to augment the M43.
Concealment is not cover.........