Of Optimal Barrel Timing, Choosing Powders & Paper Ballistics

Started by gitano, June 29, 2006, 02:37:20 PM

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gitano

Well, I've been "hard at it" trying to come up with a calculation of some sort of Figure of Merit that incorporates Optimal Barrel Timing and the output of QuickLoad. Here's the latest version.
 
The "Score" you see in the 11th column is derived from evaluating velocity, chamber pressure, barrel timing and efficiency. The equation looks like this:
 
ABS ((ABS (MAX ($D$12:$D$37)-D12))/50+1/(ABS($G$3-E12))*1000-(ABS('OBT Tool'!$O$36-G12)*1000)-ABS(MAX($J$12:$J$37)-J12)/10)*10
 
Yikes! Lemme explain. (ABS means "take the absolute value" - in other words, ignore whether the value is positive or negative).
 
The first term - ABS(MAX($D12$:$D$37)-D12)/50 - calculates the difference between the velocity produced by the powder in question (located at cell D12) and the highest velocity produced by any of the powders in question (determined by MAX($D$12:$D$37)), then divides that difference by 50.
 
The second term - 1/(ABS($G$3-E12))*1000 - subtracts the value of the chamber pressure of the powder in question (located at cell E12), from the maximum SAAMI chamber pressure (located at $G$3), takes the inverse of that number, and multiplies it by 1000.
 
The third term - (ABS('OBT TOOL'!$O$36-G12)*1000 - calculates the difference between the actual timing of the powder in question (located at G12) from the "ideal" barrel timing for a barrel of the specified length (more on that later), and multiplies the difference by 1000.
 
The final term - ABS(MAX($J$12:$J$37)-J12)/10 - calculates the difference between the "efficiency" of the powder in question (located at J12) from the highest efficiency produced by any of the powders in question (determined by MAX($J$12:$J$37)) and divides the result by 10. (Efficiency is the muzzle energy in ft-lbs, divided by the charge. The units are ft-lbs/grain.)
 
The initial "ABS", and the final "*10" simply get the "Score" to a positive value, and scale it so that we're not looking at differences of 0.01 in "Score".
 
I'm sure it'll help to walk through an example. Let's use the numbers from the first table below.
 
The powder with the highest Score is Alliant Reloder-19. The charge is 46.72 grains; the % of the case used by that charge is 100; the velocity is 2804 f/s; the max chamber pressure is 56091 PSI; the amount of powder burned before the bullet exits the bbl is 98.3%; it takes 1.2290 ms for the bullet to exit the muzzle; the pressure at the muzzle is 12705 PSI; and the resulting Score is 0.2. Here's how we get that score:
 
First, the max velocity in this group is 2874.6 f/s. Therefore, 2874.6 minus 2804.4 equals 70.2 f/s. 70.2 divided by 50 equals 1.404. Therefore the velocity "score" is 1.404.
 
Second, the maximum SAAMI chamber pressure for this cartridge is 61641 PSI. (Pounds per square inch.) The chamber pressure for the Rel-19 load is 56091 PSI. The difference is 5550 PSI. The inverse of that is 0.00018 SI/P (Square inches per pound); multiplied by 1000, we get 0.18.
 
Third, the "ideal" timing for node number 5 for a 24" bbl is 1.22852 ms. (More on "timing" later.) The timing for the Rel-19 load is 1.22897. The difference between the two is 0.000448 ms; times 1000 equals 0.448.
 
Finally, the maximum Efficiency among this group is 63.51 ft-lbs/gr. Rel-19's Efficiency is 52.32 ft-lbs/gr. The difference is 11.19 ft-lbs/gr; divided by 10 is 1.119.
 
So, we have... 1.404 + 0.18 - 0.448 - 1.12 = 0.018 * 10 = 0.18
 
Rounded to a single decimal place, that's 0.2.
 
Let's look at a powder with a lower Score – say I3031.
 
Velocity is 2732 – velocity score is 2.85
Chamber pressure is 59311 – chamber pressure score is 0.429
Timing value is 1.2290 – timing score is 0.505
Efficiency value is 61.10 – efficiency score is 0.241
For a Score of (2.85 + 0.429 -.505 -.241)*10 = 25.34
 
In closing, let me explain the multipliers/dividers a bit. The variables; velocity, chamber pressure, timing, and efficiency all have vastly difference scales. In order to insure that one did not have undue influence simply due its scale, each needed to be appropriately resized. Differences in velocity aren't too big a deal to me. Therefore, it takes a difference of 50 f/s to equal one whole point in the final Score. Chamber pressure is very important to me, but chamber pressure is measured in tens of thousands of units. Hence the inversion and subsequent 1000 multiplier. Ditto WRT the Timing variable – the differences are measured in micro-seconds, hence the 1000 multiplier. Efficiency wasn't that important to me, so it takes a difference of 10 ft-lbs/gr to make one unit of difference in the Score.
 
This is just the first installment. Next come what this means to building a rifle – namely barrel lengths. There are some very interesting results. If you stayed this long, stay tuned. The best is yet to come.
 
Paul
Be nicer than necessary.

gitano

Here's the data for the same bullet in the same cartridge with the barrel 2" longer.
 
Paul
Be nicer than necessary.

gitano

Here it is for a 28" bbl, using the "fastest" timing node.
 
Paul
Be nicer than necessary.

gitano

And here is the data for the same 28" bbl, but using the "slow" node.  This illustrates the significance of barrel timing. After yu've had a chance to digest this a bit, We'll discuss it.
 
Paul
Be nicer than necessary.

sakorick

Hello Paul. I don't own a 6.5-8mm, however, I just don't understand why you are going through this drill.......I know, you love math and plugging things into spread sheets, but quite frankly, this post has put me out to sea. You have so many scales and variables it seem impossible without applying your own weighted averages based on your experience.
 
Then, how do you intend to confirm the data?
 
You might come up with the load/barrel length matematically but what happens when the real world kicks in? What about barrel perfection?
 
It looked to me like my IMR4064 was right up there, but what happened to IMR4831? Retumbo is the most spastic powder I have ever used and it scored well. If you come up with an optimum barrel length of say....29 inches, it would not be feasible in a hunting rifle. Far be it from me to rain on anyone's parade, however, I guess I'm not smart enough to figure out what your end state/goal is. Regards, Rick.
Talk to yourself. There are times you need expert advice.

gitano

No sweat Rick. :cool:  Your question/statement is perfectly reasonable. Lemme 'splain a little of this.

As I fiddle (paper-whip) this stuff, the smoke is really clearing on some long-standing "issues" I've had. Most notably is the oft-touted "inherent accuracy" of a particular cartridge, or the converse, a cartridge that "just won't shoot". Both of those "things" bug me, because they don't make sense from a physical perspective. If you'll stay with me through the tedium of the tables, I think I can illustrate what I'm getting at.

I'll explain in words, then follow with the charts. By the way, the reason the charts are so 'busy' is that I don't want to "offend" anyone by leaving out their favorite powder, adn there are some very interesting numbers off to the right. We can discuss those later after I clear up, hopefully, the bigger issues.

First, I chose the 6.5-08 because very few people have one. That way, I don't get caught up in "Well mine does better than that" stuff. However, I just completed an analysis of the .308 Win, and the .338 MAI... both of which I have and have pressure sensors attached to. What's showing up with this analysis is that "accuracy" is tied directly to bbl length, and longer bbls don't necessarily shoot faster IF you keep in mind accuracy. Furthermore, the reasons behind the oft-observed situations where either 1) a rifle shoots most accurately at a relatively "slow" muzzle velocity, or 2) it shoots amost accurately right at the point where signs of pressure start showing, (with a corresponding high MV), are becoming clear.

In the .308 Win, I analyzed four bullet weights - 110, 130, 150, and 180 - and five barrel lengths - 20, 22, 24, 26, and 28 inches. Here's another matrix :o of the MVs for each length bbl and each of the bullets. Note that as bbl length goes up, MV does not necessarily go up. (I chose the MV of the powder with the best score.)

. . . . 110 . . . . 130 . . . . 150 . . . . 180

20" . 3188 . . . 3008 . . . . 2701 . . . 2628/2518

22" . 3188 . 3150/2976 . . 2925 . . . 2619

24" . 3161 . . . 3181 . . . . 2875 . . . 2645

26" . 3115 . . . 3137 . . . . 2842 . . . 2570

28" . 3515 . . . 3092 . . . . 3055 . . . 2837

Let's take 'em one at a time.

The 110 MVs go steadily down from 20" to 26", and finally go up - dramatically - at 28". The reason is, the timing nodes for the longer bbls. The max chamber pressure is fixed, regardless of bullet or barrel length. If you make the barrrel longer, the timing changes. So even though you can make the bullet leave the muzzle faster with a longer bbl, if you're trying to make it leave at a specific time (a node), then you won't get any increased velocity until you get the barrel long enough to "jump" up to the faster node while keeping the pressure within specs.

There are two good examples at the 20" 180 and the 22" 130. For both of those, you'll see that there are two MVs. That's because there's just enough pressure headroom, to 'catch' the "faster" lower timing node. However, in these cases, of the hundreds of powders to choose from, there is only a few (sometimes only ONE) powder(s) that actually stay(s) within the pressure limits AND keeps the proper timing.

In the 130, the MVs actually go down from 24 to 28 inch bbls.
In the 150, they go up, then down then back up, as the MV, chamber pressure and timing nodes 'align'.
The same is basically true in the 180.

OK, so what's the bottom line? You're right about barrel vagaries and other variables. However, I'm not looking for the "exact", "right" bbl length from this exercise. What I'm looking for, is a choice of powders, with an attendent MV, for a specific bullet, and barrel length. What this analysis provides for the .308 Win is a short list of pwders (all those with scores lower than "10"). From that list, I can pick the one I "like" to use, and that has the most pressure "head-room". That pressure head-room allows me to fiddle with seating depth and charge in order to fine tune the load to account for those variables you mention. This analysis tells me that the 130 grain bullet is the most difficult (least choices of powders, and least pressure head-room) of the four bullet weights I chose, to get to shoot acccurately from a 24" barrel.

Finally, if I were putting a rifle together, I'd select a bullet or two that I thought I would shoot most frequently, and I'd work on estimating that barrel length that would give me the widest "sweet-spot" with respect to powder choices and pressure. After it was built, I'd fine tune the loads by using seating depth and charge.

A "view through the haze" is what I'm after here, not a view through a microscope.

Hope this has made a bit more sense.:)

Paul
Be nicer than necessary.

sakorick

Pretty interesting once you study it awhile. I guess I'll keep getting along with RL22, 4064, 4831 and 4350. I really can't afford to stockpile lots of powder. I've never even tried Vitavouri....heck, I can't even spell it!:D I probably will stick with the 22-24 inch barrel....longer ones just seem to get in the way. Keep up the good work, Paul. Regards, Rick
Talk to yourself. There are times you need expert advice.

gitano

Actually Rick, NOT having to "stockpile lots of powders" is one of the primary reasons I'm going through this exercise. The results I'm getting hin the final analysis are very interesting - especially with respect to reducing the list of powders one "needs". The next post I make in this thread should "close that loop". Hopefully later today. I appreciate you hanging in there. :)
 
Paul
Be nicer than necessary.

Brithunter

Hi Guys,

    Hmmm all that information makes my head hurt :o :confused: but if your ideas come to bear fruit and I can slim down the powders I have by a few it would be most helpful indeed :D  Please keep up the good work Paul;)  Just because I don't understand it all does not mean that I am not interested :eek:  just confused :confused: :o .
 
    I wonder how using your formulas H335 comes out in the 30-30 at pressure equal to the .308 using 125-130 grain Spire point bullets. This is the combination I use in that Medwell & Perritt rifle but if a different powder show promise then I would be daft not to look into it :p .
Go Get them Floyd!

gitano

When trying to include the plethora of powders available, the data tends to get a bit "dense". I appreciate you guys hangin' in there. I think this final table will clear the smoke... I hope so anyway.
 
In this table, you have all of the powders that "make the cut" when looking at 4 bullets and 5 bbl lengths for the .308 Win cartridge. "Making the cut" means that you could actually fit enough powder in the case to make the bullet "go" (between 75% and 115% of case capacity), and the chamber pressure wasn't above the SAAMI max.
 
The number you see in the cell across from a powder and down from a bbl length is the "score" it got relative to all the other powders that "made the cut". This "score" is strictly based on the "best" - meaning the highest velocity, the lowest pressure, the closest to the timing node, and the most "efficient". None of those scorings required any "scaling" or manipulation by me. They are simply the basic math of ballisitcs - namely velocity, pressure, timing, energy, and charge.
 
Look at the first row - I3031 - for the 20" bbl with the 110-gr bullet it was 3rd out of all the powders. For the 22" bbl it was 1st. For the 24" bbl it was first. In fact of the 20 possible bbl lengths, I3031 provided the fastest MV, with the lowest chamber pressure, the best timing and the best efficiency, for 7 of them. It was in the top 4 for 16 of them.
 
The right-hand three columns are the Average Score, the Sum of all the Scores, and the Sample size (N). Some powders (4 of them), only "made the cut" for a single bbl length and a single bullet weight.
 
Here's the point.
 
1) QuickLoad, Load From A Disk, loading manuals and gun-writers (ptooey), list hundreds of powder from which to choose. I really wanted some way to sort the wheat from the chaff and narrow my choices to something reasonable - say 5 or 10 "good" powders from which to choose when working up loads for a specific cartridge.
 
2) I wanted to figure out how to get the Optimal Barrel Timing theory "into the mix" as I tried to select what would be close to the most accurate load for a specific bullet and barrel length.
 
3) If I was gonna build a rifle, ala the .338 MAI that Ol' John conceived - I wanted a way to focus in on what bullet, powder and bbl length combinations might prove to be the the most satisfying to me.
 
Here is my perspective on the results.
 
I'm kinda flabbergasted at I3031's "performance". Even acknowledging that this is only "paper-whipping", I3031 is head and shoulders above most of the other powders. Only I4895 and H335 even get close. I was never a big I3031 fan. However, this analysis and its results explain why I3031 may not have "worked" for me in the past. I was always striving for the highest velocity I could get while still trying to get the best accuracy. Clearly, when OBT is considered, max velocity and best accuracy, are often mutually exclusive. I will now strive to match bbl timing to bbl length, charge, and bullet weight.
 
As for me, I'm gonna give I3031 a seriously hard look for my .308 Win load workups. I'm not interested in "convincing" anyone else to quit using their favorite powders, nor am I interested in "convincing" anyone to limit their powder uses. This analysis is for those that might be wanting to "experiment" a little, or are considering taking on a rifle-building project.
 
Oh yeah, I should add that the 185 and 200 grain bullets in the .338 MAI with a 26" bbl look "very good", and Ol' John came to that conclusion without the 'benefit' of any of the above analysis. :) However, even though I have a pretty good load worked up for the 200 grain CT-BST I'm still working on the "best" choice of powders. "Things" actually might get even better. :)
 
Quote[/COLOR]
I wonder how using your formulas H335 comes out in the 30-30 at pressure equal to the .308 using 125-130 grain Spire point bullets.
[/COLOR]

I'll have a look at it, BH.

Paul

[/SIZE]PS, I'll try to make the table a bit more "readable" - we'll see how it comes out.
Be nicer than necessary.

sakorick

Hello Paul. My old Hornady book lists the 3031 in every bullet weight. In the comments section, it says "N202 IMR4064 and Win748 gave the best results throught the range of bullets". Their test rifle was a Winchester Mod70 with a 22 inch barrel, 1 in 12 twist. It also states "the 308 is not "finicky" about the powder it uses". The 3031 also showed the best results in the 168 and 180gr bullets.......interesting considering the twist.
 
My friend, you might have something going here. Can't wait for the real world data. Regards, Rick.
Talk to yourself. There are times you need expert advice.

Nelsdou

I'm a bit late to the party, but mighty interested to see how the integration of the barrel timing theory might play out in load development.
 
I find the barrel length predictions for the 308 Win facinating, but reasonable.
 
If I remember right, Paul you were considering the optimum barrel length on that 338 MAI to put you into the "sweet spot" for a family of loads. I take it this work may lead up to that. Any conclusions on that yet?
 
I've got a couple of k98's in 7.62 I'd be willing to experiment with I3031. And I just happen to have some 110/150/165/180 bullets on hand too. No chrony, but I shoot for accuracy and watch for pressure signs.
 
Nels
Put it into perspective; we live on a rock hurtling through space, what could be scarier than that?

Nelsdou

Another thought on the I3031 for the 308 Win.

In my circles you just don't hear much on I3031 as a "go-to" load for the 308 Win, but it is mentioned often in the older reloading manuals.  H'mmmm.

I pulled out Ken Waters' Pet Load book and looked at his load testing on the 308 Win dating back to 1979. His work included I3031 in all the loads from 110 to 200 grain bullets; and all showing pretty fair velocity results for it (I3031).  However, none were noted as particularly spectacular for accuracy.  His accuracy powder candidates were Norma N-202, H322, and H4895; but for individual loads.  

I found it interesting, and perhaps of some corelation to Paul's work w/Quickload the following quote: "As usual, the single based IMR 3031, IMR 4064, IMR 4895, and IMR 4320 gave their expected reliable performances.  I was somewhat surprised, in fact, at the charge weights of IMR 3031 that could be used without running up pressures, and have a higher regard for it as an all-around powder for the .308 since carrying out these latest trials."

Ken's load test results included 40.0 grains of I3031 behind a 200 grain Speer RN achieving 2478 fps, a near max load.  Not too shabby for what I thought was a powder for the lighter weight bullets.

Paul might be on to something here, and I may try some I3031 to satisfy my own curiosity.  Maybe do some hard-cast loads as well.

Nels

Put it into perspective; we live on a rock hurtling through space, what could be scarier than that?

gitano

Thanks for that info Nels. I helps clear the 'fog' a bit more. Ken Water's Pet Loads was part of the foundation for the Optimal Charge Weight theory, which in turn spawned the Optimal Barrel Timing work. Maybe if we combine the "good" burn characteristics of I3031 with proper barrel timing, (optimum MV), as opposed to trying to get the most accurate AND fastest MV, things will snap into 'clear view'.
 
I have been on the run for the past two weeks, and haven't been able to get back to the paper-whipping, let alone the range. Unfortunately, the next four weeks don't look much better with respect to the range. I am going to make a genuine effort to get some 8x56R (with a variety of powders and bullets) and .308 Win (four bullets and only I3031 powder) loads loaded and shot, but... "the best laid plans of mice and men".
 
Thanks again for sheding some more light on this subject.
 
Paul
Be nicer than necessary.

LLANOJOHN (deceased)

Paul & others......

Most..most..interesting, brother Paul!:D I have been doing my best to assimilate most of the data you have provided and I think I finally am able to comprehend all of the "expected" results. I am happy that you chose the 6.5-08 (aka .260 Rem) as one of the cartridges to "paper whip"! As you know the medium range varminter I am "still" in the process of building is chambered for the 6.5-08 AI and bullets chosen are from 85 to 100grains in weight. The data you have provided does give me some indicators for powders that should work and, of course, what I have in stock. I am of the opinion that Accurate XMR 4350 is probably a pretty good choice for beginning load work-up for the 25" barrel on the Rem 788 action.

Thanks for all your efforts in providing the data on OBT, OCW...etc. Greatly Appreciated thar, amigo!:D

Ol' John
Life Member-NRA-TSRA
Riflesmith-Bolt & Lever Centerfires Only
Left-Hand Creek Rifles
Mark Twain was right-"There is no such thing as too much good whiskey!"
My best advice.."Best to stay outta trees and offa windmills!"

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