108 v 123...what's the deal?

[DJL2]

Here is the speculative part...
Lapua 108 gn Scenar, advertised @2700 fps...assumption is 2600 fps from my barrel. WPA 100 gn produces 2630 and is said to be "light" - this seems reasonable.
Hornady Black 123 gn ELD-M...assumption is that @2410 fps from my barrel is attainable, despite chrono oddities during my last session.
Last Assumption: the JBM library values for the projectiles considered are accurate.

Using JBM's Calculator, the 108 gn Scenar stays super sonic longer (perhaps 25-35 meters, the ELD-M is calculated sub-sonic @ 850, the 108 gn Scenar between 850-900m), features less drop and the same windage correction @ 1000m. Dropping the velocity from 2600 to 2550 yields a "wash" - they go sub-sonic at nearly the same range (still a slight edge to the Scenar), the Scenar is still "flatter," but now it requires 3.7 mils for a 10 mph crosswind versus 3.6 mils for the ELD-M. The story is much the same for the 107 gn SMK. That is to say, with a head start of ~150 fps, the 108 gn outpaces the 123 gn stuff to 1000m and is nearly identical in wind deflection.

Given the popularity of the 123 gn loads, I infer that one/some/all of my assumptions are incorrect. Can my fellow forumites help show me the light? I note that when comparing the 123 gn SST, which clocked 2440 fps for me, the balance shifts notably in favor of the SST (using Hornady's stated .510 G1 BC). The SST is calculated super sonic to 950 meters, out pacing everything else considered so far, with only 3.2 mils of drift and middling drop.

The whole thing is a bit of a head scratcher - I'm looking to experiment with ammunition selection, but I'd like to narrow the field a bit before I start. I'm trying to discern where my hard earned dollars will go their furthest. It seems like Precision Firearms is about my only choice for something that isn't Hornady or WPA...and $80+ a box means that it would cost me like a grand to shoot through their whole catalog. I'd rather narrow it down to ~4, spend my $350 and go from there...to say nothing of the fact that about 10-20 rds per 50 rd box is really all I need to do an initial test...so, I already know about $100 of that $350 is going towards make nice, once fired brass.

[LRRPF52]

No, you're on the right track when comparing to the Hornady 123gr stuff, but the 123gr SMK and 123gr Scenar have much higher BCs than the 123gr SST or ELD-M.

If you put a 107gr SMK next to a 123gr AMAX or ELD-M, it's a very aerodynamic bullet with a significantly longer boat tail. The Litz BC on the 107gr SMK is .461/.230, and .468 for the 123gr AMAX.








You can get the 107gr SMK going much faster than any of the 120-123gr bullets, so hit probability is higher than a 120 or 123gr with the same BC, because wind drift will be less, as will trajectory and ToF. Recoil and sight recovery are noticeably better for me as well, so I'm leaning more to the 107gr as a go-to bullet that I need to shoot more.

Cost of the 123gr Hornady bullets has been very economical, so I stacked them deep a long time ago and continue to shoot them for that reason.

[Kswhitetails]

at specific distances, I would think that your quandry would be further solved my determining the real purpose of the bullet. If you're out to target bang/punch, I would think the lesser weight, higher velocity pill to fit that bill to a T. Typically, lighter weight and target purposed bullets tend to be cheaper. At that point the only real advantage you gain in the 123 gr bullet is retained energy, which only makes sense way back before the sound barrier anyway, punching holes in more mobile targets.

Hornady developed the ELD line specifically because they discovered that at distance, the tips of the SST and AMAX lines were deforming. They were thus less reliable and detrimental to the long range performance of those bullets. I wouldn't count on the 2D calculator treatment of the SST to be accurately repeatable at the range. In the case of the SST, as a hunting projo, it's intended purpose dwindles rather quickly beyond 350 meters for the vast (99.9%) of shooters. I would submit that most of that remaining .1% are normally using a heavier, more long range purposed hunting bullet anyway.

There are many here WAY more qualified to comment, so take this with a grain. I would say though, that if 1000 is where you want to be, if you're not hand loading your own, $350 spent at PF for custom precision ammunition is pretty normal. And as you say, you have the added benefit of selling your newly empty brass to guys like me that horde it for "later"...

If you're wanting to hunt at long distance, there are other higher BC 6.5s available. The Bergers and the ABLR come to mind.

[StoneHendge]

You want to use a G7 model once you get out past 400-500 yards. G1 declines with velocity.

Also, you want to look at where you start to approach the "Transition Zone" which starts at around Mach 1.2. Although it's incredibly difficult to directly observe, the theory is that a bullet starts to destabilize in this area. Most likely in the form of increased yaw which can ultimately lead to tumbling. As a general rule of thumb, heavier bullets will "transition" better as well as handle the shock wave better as it goes subsonic. And a bullet that has destabilized but remains somewhat on track while transitioning will probably not do very well as it goes subsonic.

[LRRPF52]

The bigger factor I'm seeing on transition is twist rate. Keep in mind that none of this is a factor within 600-700yds with most centerfire bottlenecked rifle cartridges with Spitzer bullets. Like StoneHenge said, the G7 model is more appropriate once you get past 600yds. G1 models are really appropriate for flat-based Spitzer bullets, whereas G7 works better with boat tails and distance. Doppler data works even better.

The tighter average twist rates of 6.5mm bores seem to help a lot to keep the gyroscopic stability tight through transition.

I first noticed this with my 16" 1/7.5" twist pipe slinging 123gr AMAX out to 1200yds like I was shooting at 600yds. (I was at 4400ft above sea level, 80˚ F temp.)

[StoneHendge]

LRRPF52, do you think 1:7 is getting too fast? X-Caliber will do it in a Grendel now (as well as 1:8) and they are one of the options I'm looking at when I rebarrel my 18er in the next 6 months or so (I'm aesthetically restricted to a MLGS by my monolithic upper).

[LRRPF52]

When Bill did his fleet testing, he found that 1/7.5" worked best for stability for 18" or less barrels.

I don't see how a 1/7" twist would hurt on an 18" compared to a 1/7.5".

[DJL2]

@ LRRP - thanks, that is a really solid info graphic, much appreciated.
Great info from all.

I had my first stint with the Magneto Speed on the range today courtesy of a fellow shooter. Naturally, as a classic introvert, I forgot to ask his name...really solid dude though. It was 26 C today, as opposed to 20 C on my last range outing, and sunny...my chrono was no good at all.

[Kilco]

My father and I tried the 107 SMK relentlessly in his 20" HB Howa mini when he first purchased it. At our elevation, 600 ft asl, at roughly 2650 fps we found Sierras data to be true.

https://www.sierrabullets.com/store/product.cfm/sn/1715/264-dia-65mm-107-gr-HPBT-MatchKing

A .406 G1out to 810 yards was spot on.

When I pushed this bullet 3200 fps from my 260 Rem I also found Sierras data to be almost spot on. Looking at my log book I was punching in a .455 G1 for dead on hits out to 810.

Now 810 isn't really far enough to be "make or break" data, but for our uses it was pretty revealing.

[LRRPF52]

I'll have to shoot the 107gr SMK at 1000yds and see what it does from 2625fps mv.

That boat tail on it is way long for it to have such a low BC really, especially when you look at it next to the 123gr AMAX and still use the Litz BCs.

The Litz BC is what I'm looking at, which is usually averaged over the different flight regimes.

[Kilco]

Tell me about it! I have 500 of the 107 SMKs I purchased specifically for my Grendel.. these things are just as long and more sleek than the 123 AMAX for sure.. and as I mentioned we only went our to 810 yards.. maybe going to 1k or better they will truly shine..

.406 even felt low to us considering the 100gr eld-m is a .385 and it's nowhere near as long and sleek as the 107 SMK.

I ran into the same thing using the 155 Scenar out of my 308s years ago. In my 20" setup, the 175 SMK going 2590 was walking all over the 155 Scenar@2740.

When I used the same bullets and loads in my 26" 700P, the 155 Scenar @ 2900 was a far better performer than the 175@ 2660.

[The Profit Joseph Sith]

Good thread guys, thanks for the info.. LRRPF52 thanks for the side by side those are kinda invaluable.

[DJL2]

Well...no way my wife misses that charge at month's end...

107 gn SMK and 108 gn Scenar in bound - hoping for good results with the SMK, grabbed the Scenar just to cover my bases. Will likely continue to sling ELD-M in the near term due to economy and availability while I accumulate brass and components...and, eventually, a reloading setup.

This makes me nostalgic for the days when I could find smoking deals on 6.5x55mm Lapua...must be ten years ago, or so...was stock piling it in every weight just to test it out...is Lapua loaded it, I had it. It blows my mind that Lapua brass now costs more than the actual loaded ammunition used to...and I'm not even that old!

[Kilco]

I use the 123 eld-m for its "do-all-ness".

For every area individually there is a better bullet, but for one that is affordable to stockpile, is effective at long range, explosive enough to stop varmint in their tracks, and also bring down medium game at very respectable ranges, the 123 amax/eld-m holds its own.

[GarandThumb]

What powders are you guys using with these? I tried 107 smks with 8208 xbr and got terrible results (1.3" groups) Pretty much gave up on the bullet. St The same powder with 123 elds yields consistent sub 3/4 moa groups in my rifle.

I've read on this forum that AR Comp is not a good match for the 107 but I'm tempted to give it a go anyway.

I do have some cfe223 but honestly, I hate working with fine ball powders. I also prefer to stick with temp stable powders.