Range Report I'm amazed at the difference BC makes

[Unknown]

I found some 6.5 mm 120 grain Sierra spitzer bullets at a garage sale for cheap, so I thought they would be fine for practice in my 6.5 Grendel.

Usually I shoot the 123 Scenar, and it has a .547 BC and goes transonic at 1425 yards (1006 fps)..The 120 spitzer has a BC of .386, and it goes transonic at 975 yards (1002 fps).

I knew that BC was important, but extending a rifle's range by 42% is huge. Both rounds are starting at a modest velocity of 2450 fps. I expected a difference of 20-30%...sure didn't expect over 40%!

 

[Unknown]

I shot those bullets today. Velocity was all over the place with an extreme spread of 91 fps! Average velocity for a 120 spitzer out of a Grendel was 2350 fps. Odd thing was that my rifle really seems to like this bullet. Even with that extreme spread, every five shot group I fired was 7/8 of an inch at 100 yards. With an extreme spread of 91 fps, I expected to see 1.5 inches or so.

 

[BoilerUP]

Lapua lists the 123gr Scenar as .527 G1 BC...not .547.

I think it used to be .547, but Lapua lowered it a couple years back.

 

[Advokaten]

I shot those bullets today. Velocity was all over the place with an extreme spread of 91 fps! Average velocity for a 120 spitzer out of a Grendel was 2350 fps. Odd thing was that my rifle really seems to like this bullet. Even with that extreme spread, every five shot group I fired was 7/8 of an inch at 100 yards. With an extreme spread of 91 fps, I expected to see 1.5 inches or so.

Diff in speed does not have to equal poor groups at short range, however as you allude to, it will at longer. Still the load will make for a decent training round at shorter ranges. Chris

 

[Unknown]

I was really surprised to find what Advokaten said. The other thing was that the current BC Sierra lists for that round doesn't match actual shooting. At 436 yards, and 540 I was shooting over the top of the steel. I had to drop a half MOA..maybe the garage sale bullets were an older design with a higher BC than what Sierra now lists.

This is exactly why we actually shoot to test out ballistic solutions, rather than simply accepting info. When I enter good info, good solutions return. Without testing, I have no idea if the data entered was correct or not...just like the change in Lapua's BC.

 

[Advokaten]

I know a bunch of benchresters, for 100/200 meters/yards, that really never care for es or sd,
for the short stuff this has little significanse and they place well shooting,

for anything longer than that it is very relevant, regarding the bc question, have you tried to call Sierra about them. Chris

 

[Unknown]

Never bothered to call Sierra as the bullets were from a garage sale, and the box was clearly very old. I check all rounds for seating depth to ogive, and found that although they all looked the same (136 bullets for $16) there were two lots. One lot ended up needing to have me screw the seating die in another .012 to get all bullets to the same distance to ogive. I will just use these as practice or close distance rounds.

 

[TiroFijo]

Sierra gives accurate BC numbers, but in velocity "bands". To get accurate results you need a program that can use several G1 BC values.

Lapua (llike most manufacturers) used to test bullets only at shorter ranges, thus the high G1 BC values. When they are tested at longer ranges they come up with a different BC that betters reflects the bullet behaviour at those ranges.

You can write to both makers and they'll give you more tech information.