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More .358 Steyr Number Crunching
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Old 05-21-2016, 06:27 PM
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Default More .358 Steyr Number Crunching

(I'll miss Don's comments on posts like this one.)

So keeping the 'back story' short, I have taken care of the stuck case and other issues with the .358 Steyr and am ready for the 'final hurrah'. If it doesn't 'behave' after this, the barrel will become "something else", and I'll use the receiver for a different rifle.

I am heading to the range using 225 Accubonds. I want it to shoot at most 1.5 MoA at 100 yd. In prep for that, I have as usual been hard at it with QuickLOAD (QL). There have been some surprises. First order of business for getting good data out of QL is putting good data in.

The first piece of input data is case capacity in grains of water. The .358 Steyr has a case capacity of ~78.15 grains.

Next comes the chamber length. This is not a specific input parameter to QL but indirectly it is. The maximum cartridge overall length (a QL input), is constrained by the rifle's chamber length. Getting the chamber length figure isn't difficult, but applying it within QL add a little challenge. The chamber length acts on the ogive of the bullet. One needs a way to index on the bullet ogive in order to apply the chamber length to the QL calculations. Hornady's Chamber-ALL (formerly Stoney Point OAL gauge), is a useful tool for this.

Barrel length - muzzle to bolt face - is easy.

Then it's a matter of selecting a powder. That's what this thread is about.

There are lots of characteristics of a load to consider. Most folks start with muzzle velocity, MV, letting the highest value 'drive the boat'. Some folks - some reloaders - say they "ignore" MV in favor of precision (mis-called "accuracy"), but all they talk about is velocity.

As many of you know, I have established new personal ballistic goals. (Not "standards" because I only TRY to achieve these goals. Often I am unable to.) Those goals are:

1) Muzzle energy - below 4,000 ft-lbs absolutely, and below 3,300 ft-lbs preferably.
2) Deliver at least 1500 ft-lbs to 300 yds.
3) Have a total vertical deflection of no more than 12". That means for example a max of 3" above the line-of-sight, and a max of 9" below the line of sight. This out to 300 yd, my personal maximum big game hunting range.
4) I like to keep impact velocity above 1750 f/s for best terminal bullet performance.

Those are the 'hard' numbers. There are characteristics that I "like".
1) Keep max chamber pressure below the Model K-98 Mauser (WWII bolt action rifle) max of 56,565 PSI. Preferably below 52,000 PSI.
2) Burn 100% of the powder in the barrel before the bullet exits the muzzle. Not a big deal, but something I look at.
3) PRIOR TO SHOOTING, get charge near a 'node' in optimal barrel timing theory. Actual shooting trumps ANY theoretical number.
4) "Efficient" use of powder. Absolutely last on the list of priorities, but I THINK when one 'aligns' all the different elements to their optimum values, one has a better chance of achieving overall goals - a precise system (shooter, rifle, cartridge) - that can be depended on to consistently kill humanely.

It is too easy to 'fool' oneself. Therefore, I am always looking for objective tools for 'measuring' some performance characteristic I am trying to achieve. An example would be the Minute of an Angle (MoA) as an objective measurement of precision.

After crunching through all the elements of getting a "good" load estimate out of QL, I settled on 46.5 grains of I4198 behind the Nosler 225 Accubond. This gives me 1500 ft-lbs delivered to 300 yd; muzzle energy less than 3300 ft-lbs (3165), total vertical deflection of 16 inches. (Missed the 12" goal by 4 inches.) Right on th e5th node of timing theory. But as I was looking at the numbers (because I was surprised by I4198 being the 'best' choice), I decided to calculate "efficiency" defined as ft-lbs of energy at the muzzle divided by grains of powder used. The units then become ft-lbs per grain of powder. Turned out, that the efficiency of this load was 69.5 ft-lb/gr. Hmm... I didn't have a feel for what that meant. Was that a "good" figure? So I calculated the efficiency for all of the loads that QL listed based on the input data I gave it. There were a lot of powders that were more efficient, AND a lot that were worse.

As I looked at the ones with the highest efficiency I noticed that they were the "fast" powders usually called "pistol" powders. They used a small charge and delivered a pretty high ME, BUT... at a reduced muzzle VELOCITY. So, even though they had relatively low MVs, the small powder charge allowed them to have high efficiency. I needed another 'ruler'. What was important to me was both efficiency, but also velocity. (I "need" velocity to achieve trajectory and delivered energy goals.) Since velocity AND efficiency were what I am interested in, I simply multiplied MV times efficiency. The resulting units are ft/s * ft-lbs/gr = lbf^2/gr-s. (Units aren't really important here as I'm creating a "figure of merit".)

Below you will find part of the output table of potential powders generated by QL. The first one is allowing the max pressure to go up to 56,565 PSI, and all other parameters to follow the pressure. You will note the MVs vary from the high 2775 to 2024 f/s. Red cells are "bad" in that they fall below the minimum charge needed to prevent an accidental "double charge". Green cells are "good" in that they exceed MV values that I am trying to reach to achieve ballistic goals, and the "right" timing node.

Notice the "Efficiency" and "FoM" columns on the far right.

Here is the output table when I constrained the MV to 2517 f/s. (Note that all the MVs and MEs are the same.) This MV gives me the desired 1500 ft-lbs of energy at 300 yd; the less than 3300 ft-lbs of ME; but fails to provide the 12" max vertical deflection over 300 yd. Instead it's a total of 16 inches.

Again, notice the Efficiency and FoM columns.

I find the Efficiency and FoM columns interesting. I wouldn't change anything in my load selection, BUT... if there were two or three powders that were really close in the critical values of MV, ME, timing, etc., the FoM MIGHT offer a 'ruler' to use in making an objective selection. Furthermore, it's always interesting to me to 'see' how powders relate in contexts other than the 'garden variety' that gunwriters (ptooey) uncreatively hawk. Learning about powder relationships takes the voodoo out of 'experimentation' and allows one to make considered and informed decisions. Or... one can choose to be Chicken Little and just assume the sky is ALWAYS falling.

I have attached the PDF files below. They contain the WHOLE tables. The above tables are all that could be captured in a "screen shot".

Paul
Attached Files
File Type: pdf 358 Steyr 225 AB Max fps.pdf (237.7 KB, 2 views)
File Type: pdf 358 Steyr 225 AB 2517 fps.JPG.pdf (163.5 KB, 8 views)
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358 caliber, 358 steyr, accubond, efficiency, figure of merit, fom, quickload


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