120 SMK Vs 123 SMK....what is the difference?

[lazyengineer]

What Rick Small said.

I will go for the 120 any day of the week. Works very well with any load I have tried, any OAL, any primer. Maxes out at about 800 with a Grendel before it starts going transonic.

When the 123 came out most guys found it difficult if not impossible to get consistency from a AR Grendel. With my .260 or any of the mid range cartridges I had to use a bolt rifle and hard seat it into the lands for it to shoot well.

Depends on what you want the bullet to do for you. If you want something to blast steel at good distances, the 120 will be much easier for you to get to shoot very, very, well. If you think you need what ever minor advantage you will get from a VLD design when shot from a 30 grain cartridge, then expect to spend time in load development for the 123 and do some extensive testing to make sure it will shoot well enough to meet your needs.

LR55

Thank you. This actually was very helpful.

I've grown to dislike the 123. On-paper, it's perfect bullet. In practice, it's been a nightmare of a bullet for me in the Grendel; 3 BBL's and multiple manufacturers. When I run it mag-length slamming through an AR gas system, is very expensive 3-4 MOA ammo for me.

Thinking it's me, I load it up in my Creedmoor, that I know is a 1 MOA gun. And again, 123's in a Mag-Length semi-auto magazine, give me a nice 3-4 MOA performance, even in the creedmoor. Yet when I tried some 120's this weekend, my group sizes shrank to better than half, and are even crowding 1 MOA (not quite, but close), in my Grendel.

Your post was very helpful in explaining why.