Does anyone know the Ballistic Coefficient of the M118LR 175 gr. HPBT?

.505 @ 2800 fps and above
.496 between 2800 and 1800 fps
.485 @ 1800 fps and below

Sectional Density is .264.

Sierra 175 SMK.

I've tested them and measured the BCs using an Oehler M43 in 10, 12 and 14" twist barrels of 26 and 27" length. The velocity runs 2650 - 2675 out those barrels (M70 Targets, M40s and S&L Palma rifles). The BC out of 10" twists run .48 to .49. The BC in 12" twists run .52 to .53. The BC in the 14" twists run .45 to .46. These BCs held consistent over several tests under slightly varied weather conditions.

As can be seen the 10" twist over stabilizes the bullet as noted by the lower BC. The 14" twist under stabilized the bullet also noted by the lower BC. The 12" twist proved to give the most consistent and best stabilization to the 175 gr MKs. Accuracy evaluation at 600 yards also showed the 12" twist giving the higher BCs also proved to be the most accurate. This is self evident as the measured BC tells us the 'efficiency" of the bullet in the air. The 12" twist gave a higher 'efficiency for the 175 gr MK and it proved the most accurate. It is also worth mentioning that accuracy testing at 100 yards did not reveal this as all grouped pretty much equally. Only testing at long range can reveal the true difference.

Note; Switching bullets to a load with the 155 gr Palma MK showed the 14" twist gave the highest BC and the best accuracy at 600 yards.
It is thus best to match the bullet to the twist or if you can; match the twist to the bullet of choice.

Larry Gibson

Many Thanks!!

Larry, I have a 10" twist in a 20" barrel length. Do you suppose these bullets fired from my rifle would mimick your tests with the longer 26 - 27" barrels?

quote:

Originally posted by wistrapper:
Many Thanks!!

Larry, I have a 10" twist in a 20" barrel length. Do you suppose these bullets fired from my rifle would mimick your tests with the longer 26 - 27" barrels?

Probably close to it BC wise, the velocity will be less though. Come to think of it the BC may improve some because of the less velocity.

Larry Gibson

Whatever a 175 BTHP Sierra is. That is what is loaded in the 118LR.