123 amax BC

[cst]

The 123gr SST is not the same bullet as the 123gr AMAX. The ogives are different, and the cannelure is not present on the 123gr AMAX.

When I have used the stated BC on the 123gr AMAX, I was shooting out to 1200yds, and that's with the actual barometric pressure, temperature, and altitude entered into my ballistics program. I was at 4400ft elevation. One thing about tighter rifling is that it spins the pill so much that they stay stable through transonic, so you don't get erratic trajectory after the maximum ordinate like you do with loose twists.

Even still, I'm supersonic out to 1318yds in those conditions.

What's ur muzzle velocity?

[LRRPF52]

What's ur muzzle velocity?

2460fps with the factory AMAX. My mild CFE hand loads easily make 2500fps, and max load at 50ksi is 2550fps with CFE from a 16" AA pipe for me.

If you look at the 123gr SST next to the AMAX, you can see the differences in ogive shape.

Hornady's listed BC for the 129gr SST (.485) is also wrong. They underestimated it, and Bryan Litz found it to be .495 instead. Same with the 123gr SMK, listed at .510 but is really .522 G1.

If you look at the 129gr SST next to a 123gr AMAX, the 129gr SST has a more secant ogive, but a shorter boat tail, and is a longer bullet. The 123gr AMAX has a longer boat tail, so I think it's G1 BC is closer to .5 for that reason.

[cst]

I've done some searching and a few people confirmed that the Litzs G7 for 123 AMAX is .239....seems awefully low
Hornady GMX 120Grn G1-.442 G7-.226
Hornady A-max 123Grn G1-.468 G7-.239
Hornady SST-BT 123Grn G1-.462 G7-.236
Hornady Interbond 129Grn G1-.518 G7-.265
Hornady SST 129Grn G1-.482 G7-.247

People are saying this is the values Litz has put out on his book and in the applied ballistics app

[LRRPF52]

I have a paper from Litz where he did BC analysis on many different projectiles from the major manufacturers, and it shows the 129gr SST at .495 G1/.247 G7.

There is also manufacturing variation in ogive shapes, especially on the secant pills, so it's best to confirm your data with live fire for the ground truth. Rate of twist also affects BC at long range. My 16" has 1/7.5" twist.

[NugginFutz]

I looked up the latest data I have, from Litz's "Modern Advancements In Long Range Shooting".

While he still has not provided data specifically for the 123 Amax, he does provide data for the 123 SST and both the 140 SST and 140 Amax. I acknowledge that this is simple extrapolation but, if you accept the premise that 140's can be scaled down to 123's, I think it should be good enough to get someone who's interested into the ball park.

I've taken the ratio's of the 140 Amax and SST and applied them to the 123 SST to come up with an estimate for the 123 Amax. SD=Sectional Density, i7 is the G7 form factor, followed by the G7 and G1 BC's.

Bullet		SD	i7	G7 BC	G1 BC
140 SST BT	0.287	1.082	0.265	0.519
140 Amax	0.287	0.961	0.299	0.584

123 SST BT	0.252	1.069	0.236	0.461
[I][B]123 Amax *	0.252	0.949	0.266	0.519[/B][/I]

* Estimated.

An interesting aside is that, according to Litz, form factors lower than 1.0 are better than average, and the best long range bullets have form factors below .095. Form factors above 1.05 typically have too much drag for serious long range work. Bearing this in mind, it would appear that the 123 SST would not be the best choice for long range shooting, but I am pretty sure that long range was not its intended market.

[cst]

So basically ...we don't need a BC for the 123 AMAX because everyone is using totally different figues...im being sarcastic.

It's getting fustrating that there is no common g7 available.seem like .people who are using numbers that work for them are just coming up with arbitrary values.

I know u have to confirm your data to real world dope but this is a problem. 600 yards is one thing but getting a target at extreme grendel range like 1000plus is going take a lot of missing

[bwaites]

Its pretty simple to derive what you need. Shoot a group at 100, use the G1 BC since its known. Once you have a tight group, determine the center. Using the G1 BC, shoot a group at 600 yards. Measure the difference in MOA or MIL from the expected. All you are worried about is drop. Gravity is the constant. That is your correction factor. Plug that correction factor into a good program like Ballistic AE or any other that allows correction factors. It will then calculate appropriate drop charts from that data. You eliminate the need for a measured G7 BC from the equation, because you have actual data from your rifle.

[NugginFutz]

A difference in BC of a few points, one way or the other, isn't going to make shooting 1000 yards as onerous as you might think. It could possibly make the difference between a first round hit or a few sighters, at 1000, but certainly not something that will cause a serious depletion of ammunition.

I was only trying to point out that the notion that the SST and Amax are virtually the same is flawed on its surface. In doing so, I came up with some estimated #'s for the 123 AMax. I cross checked the results I got against the published G1 BC for the Amax, and I got quite close to their #'s by scaling down the 140 grain pills. (Hornady indicates a G! of .510, whereas I calculated .519.) Using measured, field driven data, I came within 2% of Hornady's published BC.

So, what does this mean? Let's compare. *

Calculating a shot with a G1 of .510 @ 2500 fps, you get 397.4" of drop @ 1000 yards.

Bump it to a G1 of .519, and you have 393.8", a difference of -3.6" in drop - at 1000 yards!

If we switch to the calculated G7 of .266, with the same 2500 fps, you get 391.1" of drop - an utterly massive difference of 6.3" of drop from Hornady's published .510 G1 BC.

I hope you see my point. Going from one extreme to the other, the needle swings about half a foot at 1000, and that's before you consider wind, temperature and station pressure.

I recommend you relax, load up and go shoot. Take good notes, and enjoy the time behind the trigger.

(*Station Pressure set to 29.85" Hg, temp to 67 'F)