120 vs 123

[cceckhoff58]

There are a few lines of bullets (Hornady, Lapua, Sierra) that have .264 bullets in 120 and 123 grains. This is a small difference. What is the reason behind this?

[grayfox]

In general, the 120's were first made, and they have a tangent (a bit more stubby) ogive.
The 123's were made for the Grendel, and have a secant (longer, sleeker ogive) ogive. Usually also a higher BC.
The 120 is more forgiving in terms of OAL seating distance from the lands, where a secant ogive can be more picky.
A 120 will probably need to be seated a bit shorter as to OAL.
Either one can shoot fine in a given barrel.
The sierra 120 SMK is often used on here as a "proof" bullet, if a barrel can't shoot the SMK decently well, probably won't shoot anything well.

[LRRPF52]

123gr comes from European metric system since 8 grams = 123 grains.

5 grams = 77gr
7 grams = 108gr
8 grams = 123gr
9 grams is 139gr
10 grams = 155gr
10.1 grams = 156gr
11 grams = 170gr
12 grams = 185gr
13 grams = 200gr

You will notice 139gr and 156gr a lot with early 1900 century ammunition from Europe for 6.5x55 Mauser. In the US bullet market, you typically see even numbers in grains with several exceptions.

87gr came from the .250 Savage and marketing to where they could break the 3000fps barrier for a factory load. Testing demonstrated that in order to get consistent 3000fps performance at factory loadings, the 90gr bullet wouldn’t achieve those regularly enough, so they dropped the projectile weight down to 87gr and facilitated the .250-3000 moniker.

You see some carry-over of the gram-based weights in 6.5mm and 7mm in the US, especially with 139gr.

[Harpoon1]

123gr comes from European metric system since 8 grams = 123 grains.

5 grams = 77gr
7 grams = 108gr
8 grams = 123gr
9 grams is 139gr
10 grams = 155gr
10.1 grams = 156gr
11 grams = 170gr
12 grams = 185gr
13 grams = 200gr

You will notice 139gr and 156gr a lot with early 1900 century ammunition from Europe for 6.5x55 Mauser. In the US bullet market, you typically see even numbers in grains with several exceptions.

87gr came from the .250 Savage and marketing to where they could break the 3000fps barrier for a factory load. Testing demonstrated that in order to get consistent 3000fps performance at factory loadings, the 90gr bullet wouldn’t achieve those regularly enough, so they dropped the projectile weight down to 87gr and facilitated the .250-3000 moniker.

You see some carry-over of the gram-based weights in 6.5mm and 7mm in the US, especially with 139gr.

“The more I know (about the Grendel), the more I realize I know nothing!” Socrates

[muvef]

Excellent responses above.

[Dub]

In general, the 120's were first made, and they have a tangent (a bit more stubby) ogive.
The 123's were made for the Grendel, and have a secant (longer, sleeker ogive) ogive. Usually also a higher BC.
The 120 is more forgiving in terms of OAL seating distance from the lands, where a secant ogive can be more picky.
A 120 will probably need to be seated a bit shorter as to OAL.
Either one can shoot fine in a given barrel.
The sierra 120 SMK is often used on here as a "proof" bullet, if a barrel can't shoot the SMK decently well, probably won't shoot anything well.

Thank you for all the insight.

Really helpful.

[Stugotz]

123gr comes from European metric system since 8 grams = 123 grains.

5 grams = 77gr
7 grams = 108gr
8 grams = 123gr
9 grams is 139gr
10 grams = 155gr
10.1 grams = 156gr
11 grams = 170gr
12 grams = 185gr
13 grams = 200gr

You will notice 139gr and 156gr a lot with early 1900 century ammunition from Europe for 6.5x55 Mauser. In the US bullet market, you typically see even numbers in grains with several exceptions.

87gr came from the .250 Savage and marketing to where they could break the 3000fps barrier for a factory load. Testing demonstrated that in order to get consistent 3000fps performance at factory loadings, the 90gr bullet wouldn’t achieve those regularly enough, so they dropped the projectile weight down to 87gr and facilitated the .250-3000 moniker.

You see some carry-over of the gram-based weights in 6.5mm and 7mm in the US, especially with 139gr.

I was always curious about the odd numbers...