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

[CJW]

The Great Unwashed,

What is the difference in these 2 bullets other than 3 grains in weight.

Which do you prefer?

Chuck

[ricsmall]

The 123 is more of a secant ogive with a higher BC. The 120 is a tangent ogive and lower BC.

[A5BLASTER]

The 123 is more of a secant ogive with a higher BC. The 120 is a tangent ogive and lower BC.

^^^^what he said.

I want that 123 every time no matter if it's the smk, sencar, eld-m or nosler cc.

[LR1955]

The Great Unwashed,

What is the difference in these 2 bullets other than 3 grains in weight.

Which do you prefer?

Chuck

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

[ricsmall]

I’m with ‘55 on preference. Go with the 120 grain. I got the 123 to shoot well in the one rifle I tried it in, but it was a bartlein barrel that never shot more than 1moa with any load tried, and shot factory out to 940. I was a fool for letting that barrel go.

[LRRPF52]

Some of the most accurate loads I've shot over the years have been with 123gr SMKs, including at distance.

With the PF ammo, I lost track of how many rounds were going into bughole groups, but I've always shot them through SAAMI chambers with the compound throat.

Looking at the BCs and the type of shooting I do, I'll probably never load any of my 120gr SMKs.

Their ogive seems like they would prefer a conventional throat with parallel freebore.

The 123gr SMK has one of the best BCs for TGT bullets in that weight class, almost identical to the 123gr Scenar.

I'm using Litz BC values, not manufacturer stated G1 values.

Not trying to be contrarian, just relating what I've seen with 123gr SMK.

I love that bullet.

[CJW]

Very interesting guys.......

Which powder do you like for the 120, 123?s....

[A5BLASTER]

Very interesting guys.......

Which powder do you like for the 120, 123?s....

My new love is ar-comp. Tryed cfe223,leverevolution,ppv and while I worked up great loads fast and accurate. The sd and es numbers never were as low as I would have liked and where I live, if the air temp swings 20 or more degress the load would fall apart.

Tryed ar-comp and the sd and es numbers are much better, groups just as tight as any load I worked up before and it's temp stable. Velocity's are much any diffrent in my rifles.

[ricsmall]

I use 8208 for both. 28.2 grains was my accuracy load for the 123. Can’t remember for the 120. I’ll look it up in a bit

[LRRPF52]

I used TAC under the 120gr SMK when I first started shooting Grendel based on recommendations from this forum about 10-11 years ago.

I think all the 123gr SMK loads I've shot have been factory.

I think PF was using 8208XBR back then in Lapua brass.

All the 123gr SMK ammo I've shot has been Lapua brass.

You put in quality components and load procedures consistently through Bartlein or Krieger barrels and you get extreme accuracy results.

Same with 123gr Scenar and the 120gr Scenar-L.

[CJW]

You boys are just damn rocket scientist, alway so, so helpful.

This is the only AR board that has only gentlemen on it.

[glk45]

You boys are just damn rocket scientist, alway so, so helpful.

This is the only AR board that has only gentlemen on it.

You got that right.

[FLshooter]

My Bartlein heavy barrel loves 123g SMK.I use H335 powder and the groups are sub 1/2”. I have shot the 120g smk.They are also very accurate. But if I can find them,I go for 123 g because of the higher ballistic co efficient.

[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.

[LR1955]

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.

LE:

Basic difference between a Tangent and Secant ogive. Look at any of the bullet maker web sites and all of them say the Secant or VLD designs are more sensitive to seating depth and chamber design. Also, their BC's are variable with the highest being when the bullet is driven way faster than a guy will get from a Grendel cartridge due to powder capacity. Yes, the VLD's show slower incremental decreases in velocity over time than the Tangent designs and any time a guy can get his bullet to the target faster is better because the wind has less time to push it around. The other side of the sword is that getting there faster means nothing if a guy shoots 8's at 600 or misses targets at 800 because he didn't get the right seating depth, use the right chamber design, or the right rifling twist.

If a guy wants good results with almost any safe load using any chamber and conventional twist rate, and without spending a couple hundred on components to run ladder tests using different powders and primers at the longer ranges they are shooting, get a bullet with a Tangent or even a Hybrid ogive. I have found the Lapua 108 and 123 grain bullets to be a super good compromise between the more strict VLD's like the 123 Sierra and the Tangent ogives like the 120 Sierra. The problem is the Lapua bullets are so expensive that most guys will not buy them unless they are highly competitive and have found these bullets to be the difference between winning and losing.

The 120 Sierra will be fine on two minute steels to 800 yards at sea level providing a guy can dope winds as well as they could shooting the old 168 grain Match King loads used in High Power years ago. Granted, these loads are not competitive anymore because of their low velocity compared to the various 6mm and 6.5 mm cartridges used competitively today but at least with these loads you can bet that poor performance wasn't due to the bullet.

LR55

[LRRPF52]

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.

My Bartlein .260 Rem gas gun barrel will shoot any of the 123gr Target bullets into bug holes for sport, with .5 MOA groups at 500 and 1000yds easily, even in the wind.

The only target bullet I didn't get to shoot well through that barrel was the 140gr A-MAX for some reason, but I didn't spend much time with it because the 139gr Scenar, 130gr VLD, 123gr Scenar, 130gr Norma Golden Target, and 142gr SMK shot so well.

I specifically had that chamber throated for the standard/short COL limited by the magazines with VLD/Secant ogives in-mind.

For anyone that is trying to get secant ogive bullets to shoot well in long freebore chambers (that economy barrel-makers like to use instead of the SAAMI chamber) at the lower pressures of the 6.5 Grendel, good luck to you.

Like I said, the 123gr SMK has been one of the most accurate bullets I've shot through several different 6.5 Grendel AR15s, but they all had SAAMI chambers with the compound throat and have all been Bartlein or Lilja barrels.

107gr SMK shoots amazingly well on top of 8208XBR in 6.5 Grendel too using the same formula.

If you have a conventional freebore, I would look at the shortest radius tangent ogive bullet that will get close to the lands and play with them, but chances are you will waste many range trips chasing accuracy that is easily available on your very first trip to the range with a SAAMI chamber and any of the secant ogive, high BC bullets on the market.

For me, getting to the range is no small effort, so I can't afford to waste my time with chambers geared to a profit model that relies on volume of sales vs performance.

[Fess]

LRRPF52, what kind of change in accuracy do you see as the throats wear in high round-count rifles? I have wondered if the compound-throat chamber wears evenly or whether its shape changes to be, for example, less accurate with secant-ogive vs tangent-ogive bullets after some point. With the precisely made barrels that you use, I don't have an idea of the number of rounds fired before you would consider the accuracy unacceptable.
Thanks

[Kswhitetails]

I've seen and been told that you will notice slight accuracy changes as the throat erodes due to an increasing jump. Load incrementally longer to chase your groups again. When you see velocities dump 2-300 fps, you know it's time to change barrels. The dump will happen suddenly, in a few shots, and you'll see your accuracy vanish. It will be obvious. Re-checking your load over your chrony, you'll see the vel. loss.

My 12" build has about 2300 rounds on it, and I'm loading 12 thousandths longer than I did at 200 rounds to maintain groups. My LaRue has somewhere near 2560, and I've stopped having to load longer. I think the last time I checked dtl, was at about 1300 rounds. I will check when I notice my Benchmark and 120SMK load not doing what I expect. Since 1300, it's been money. I shoot a lot of steel through my pistol. No steel in the LaRue. Both show no issues with throat erosion that I'm good enough to track well enough to report here. From what I can tell, both throats eroded about 15-20 thou and stopped.

[LRRPF52]

LRRPF52, what kind of change in accuracy do you see as the throats wear in high round-count rifles? I have wondered if the compound-throat chamber wears evenly or whether its shape changes to be, for example, less accurate with secant-ogive vs tangent-ogive bullets after some point. With the precisely made barrels that you use, I don't have an idea of the number of rounds fired before you would consider the accuracy unacceptable.
Thanks

I haven't seen accuracy fall off yet with any of my Liljas. With the high-end barrels, you often won't see accuracy fall, but velocity will drop with throat erosion.

6.5 Grendel doesn't suffer from this really since the chamber pressure is so low compared to any of the 6.5-08 class of cartridges, and especially the 6mm Dashers, 6 Creedmoor, or 6x47 Lapua.

The Bartlein and Krieger barrels have been known for using harder stainless steel, whereas your Liljas and Shilens typically use softer stainless to get that straight bore reamed through the stock before rifling. Stainless is preferred by accurate barrel makers because it is softer than 4140 and higher chromoly steels, which do better for machine-guns and assault rifles that will have high round counts blasted through them, especially on automatic.

Throat erosion is more an issue above 55,000psi, especially with more "over-bore" cartridges like the 6mms and fat cases with smaller neck diameters.

Since Grendel is neither over-bore nor anywhere near 55ksi working pressure, throat life will exceed .308 Winchester, which is the gold standard for barrel life among accurate rifle shooters.

.300 Win Mag is notorious for throat erosion and velocity loss, to the extent that guys have experienced significant POI shift in courses.

[lazyengineer]

Some of the most accurate loads I've shot over the years have been with 123gr SMKs, including at distance.

With the PF ammo, I lost track of how many rounds were going into bughole groups, but I've always shot them through SAAMI chambers with the compound throat.

Looking at the BCs and the type of shooting I do, I'll probably never load any of my 120gr SMKs.

.....

Well I guess that's part of my frustration. I was under the impression buying a Team BBL made by purists and of the appearance of defacto endorsed by the site; I figured that the chamber would be cut to whatever the proper chamber is supposed to be, on my TEAM Monster BBL. And so in line with the above, shoot the 123's well. It didn't work out that way for me. Are the TEAM BBL's not chambered correctly?

I know your own experiences with Grendel have been exceptional with accuracy. Mine have not. At all. The cost of cutting a correct chamber is no more than cutting an incorrect dimension chamber, and PSA usually does a decent job of doing their job. It didn't work out so good, if my 123 experience is the test. So I bought a team BBL, because surely that has the correct chamber. Again, it hates 123's. Is there something unusual or exotic on your BBL's that's not standard? I'm 0 for 3, on BBL's that are as modern and recent as you can get.