Load Development at 100 yards

[Bart B.]

The idea is to identify a charge weight window that gives you consistent (minimized) ES/SD, the final charge weight will be the center of that window

What if that load causes more vertical spread at long range than one a grain or more different that has more velocity spread but less vertical spread on long range targets?

 

[rijndael]

Long Range Hunting.

If you have the old URL (that no longer works), or can recall about where it was published on the site, I may be able to dig it up.

 

[Bart B.]

If you have the old URL (that no longer works), or can recall about where it was published on the site, I may be able to dig it up.

I don't have the old URL link. Try this one:

https://www.longrangehunting.com/forums/rifles-bullets-barrels-ballistics.19/

That's the forum it was in several years ago. As best i remember.

 

[rijndael]

So it was a forum post, not an article?

If we have the exact URL, we could likely get it from The Way Back Machine, http://archive.org/web/

 

[Bart B.]

So it was a forum post, not an article?

If we have the exact URL, we could likely get it from The Way Back Machine, http://archive.org/web/

Yes, a post in the forum that link goes to. It looks different now.

I emailed Black Hills twice asking about that post; never got a response.

 

[Papa Charlie]

No. That's based on what Sierra Bullets' ballistic tech mentioned. He said their 308 Win test barrels slowly shot the same lot of components a few fps slower every couple hundred shots. Later, after 2000 rounds, a little more. Near the end of their ~3000 round life, average velocity had dropped several dozen fps.

I've noticed that velocity loss shooting at the same 600 yard range with the same load component lots and needing 1 to 1.5 MOA higher sight dope at the barrel's last 10% of accurate life.

Black Hills did a test showing 308 Win gradual velocity and accuracy degradation and the results were published on a web site that no longer lists it.

I have read this too. However a brand new barrel is not as

Mark Walker knows exactly what he is talking about, although the idea that competition barrels can apparently gain velocity as they break in is not really a "new" concept. It has been reported here regularly over quite some time. For most, it seems to happen somewhere between ~50-100 and 200 rounds, although I have read reports of it happening as late as 400-500 fired rounds.

It is also common for quality competition barrels in calibers that aren't barrel-burners such as .223 Rem and .308 Win to shoot with little or no detectable loss of precision for 2000-2500 rounds after they settle in. You will likely have to adjust the load for throat erosion and other time-dependent factors during that period to maintain precision. However, the barrel itself can still be capable of excellent precision with 2500 to 3000 rounds if you have taken proper care of it during it's lifetime. In my hands, the effects of throat erosion and fire-cracking seem to become readily apparent at somewhere between 3000-3500 rounds, but that can easily vary between different barrels and manufacturers.

Doing preliminary load development prior to a barrel having settled in is not a complete waste of time, especially if you meticulously record solid velocity data. It is usually a matter of minor tweaking to re-adjust the load, rather than completely re-doing a full-blown load development from scratch. It is analogous to working up a load in virgin versus fire-formed brass. It will probably change a bit after fire-forming the brass, but the changes are usually minor adjustments rather than huge ones.

Papa Charlie - I might have missed it, but I didn't notice that you listed your barrel length, freebore length (COAL), or the type of brass you're using. There is a huge amount of information available here on very good loads using Varget and 185 Juggernauts. More often than not, it is actually rather difficult NOT to get that combination to shoot well.

Depending on the amount of freebore the lead/throat has cut, which affects usable case volume, .308 Win loads with Varget and 185 Juggernauts in standard Lapua brass can be expected to tune in from around 2700-2730 fps (~.085 fb/~2.885" COAL) up to around 2770-2800 fps (~0.170 fb/~2.970" COAL) in a 30" barrel. Your load should be expected to tune in somewhere relative to these approximate values dependent on your barrel length, freebore length, and brass type. In my hands, Lapua .308 Win Palma brass usually has from 0.1 to 0.3 gr greater case volume than standard Lapua .308 Win brass, which can also make a difference, as do the large versus small rifle primers.

If you look solely at your seating depth data for 43.0 gr Varget, the only questionable thing I see is the .020" off group. If you possibly might have pulled one of those shots, then your seating depth test at that charge weight is exactly what I'd expect with 185 Juggernauts. That is to say, they generally tune in somewhere around .015" to .020" off the lands and then stay tuned in for several successive seating depth increments, usually as far off as I have tested them, which is about .030" off or so. In all likelihood, your 43.5 gr load is what's often referred to as a scatter node. Although the vertical is mostly tuned out exactly where I'd expect for the Juggernaut at .020" to .025" off the lands, the groups overall just really aren't too great at any seating seating depth. The 44.0 gr load seems to be slightly better and exhibits a similar effect of minimized vertical in the expected seating depth range Juggernauts are known to prefer. However, 44.0 gr may also not be close to where your setup wants to shoot.

My suggestion would be to seat the bullets at .020" off to start. This is where all the charge weights start to show minimized vertical in terms of seating depth. Then go back and test from about 42.8 to 43.8 gr in 0.2 gr increments. If at all possible, record your velocities for every increment. Look primarily for minimized ES/SD values within that window, with your secondary focus on group size/shape. The idea is to identify a charge weight window that gives you consistent (minimized) ES/SD, the final charge weight will be the center of that window. Next, carry out a seating depth test in .003" increments from about .012" off to about .027" off, all at the final charge weight you identified previously. Look for at least two successive seating depth increments that exhibit minimized group spread, ideally a single ragged hole as a couple of your groups show above. You obviously want to avoid groupings that are exaggerated horizontally or vertically. Loading to the longest (i.e. the shortest jump) of the two or more successive seating depths that exhibit optimal grouping will give you the most room for land erosion before you will need to re-visit seating depth testing.

The above suggestions are merely starting points as I don't know your exact freebore length (~COAL), barrel length, or the type of brass your using. However, you can vary those parameters as necessary based on your specific setup. The key is to optimize charge weight primarily for ES/SD, with group size as a secondary (tie-breaker) readout, then tune in the groups using a fine increment seating depth test. Essentially, that means doing exactly what you already did, except in finer increments for both charge weight and seating depth. The problem with trying to do both at the same time is that the more variables you're trying to analyze and the more groups you have to shoot, even one or two pulled shots can make it extremely difficult to get a good readout on what's happening. Isolate your variables to test one at a time; it can make it much easier to spot the trends you're looking for, even with a bad shot mixed in, than if you're trying to analyze/optimize multiple variables all in the same test.

Thanks for the detailed message.
My barrel is 30 inches, 1:10 Twist, by Benchmark.
Cases are Lapua Winchester
Primers are CCI BR-2

I can see I need to do some more refining.

 

[Ned Ludd]

I have read this too. However a brand new barrel is not as


Thanks for the detailed message.
My barrel is 30 inches, 1:10 Twist, by Benchmark.
Cases are Lapua Winchester
Primers are CCI BR-2

I can see I need to do some more refining.

Papa Charlie - This is still just a guesstimate, not knowing your exact COAL/freebore length, or velocities, but you're likely going to find your optimal load somewhere between 2720 and 2780 fps with 185s and Varget, with the bullet seated somewhere between .015" to .025" off the lands. Optimized loads with essentially your exact same setup have been listed here by F-TR shooters using that combination for years, and with only one exception that I am aware of, they almost always fall within the parameters I listed, or very, very close. In that one exception, a friend actually found it necessary to seat a particular lot of Juggernauts into the lands, but that is not the norm. The above parameters are what have worked for literally hundreds of shooters over many years with that exact same combination. In my hands, the optimal charge weight window(s) in that region for 185s/Varget tend to be 0.3 to 0.4 gr wide, so your 0.5 gr increments may be too coarse to zero in on your final charge weight. However, I'd start in the area of what has already reliably worked for many F-TR shooters over the years and then tweak it as necessary for your setup.

My guess is that this was your intention from the start, but I think your results suffered somewhat from testing in too large/coarse increments and in testing two variables at the same time, which can make it a little tougher to decipher if the test groups aren't all absolutely perfect. Cover the appropriate regions in charge weight in much finer 0.2 or 0.3 gr increments, then do the same with seating depth and I'm certain you'll find the loading parameters you're looking for.

 

[Papa Charlie]

Benchmark used a SAAMI Match grade reamer. It produced a 0.110" Freebore. I loaded a Berger 200.20X long in a dummy round for Benchmark. They used it to test the Freebore. The end result, was that when the dummy was chambered it seated the round an additional 0.004".
The rounds I am loading with the Berger 185gr Juggernauts I am using a Hornady comparitor for seating. According to it the case length to the comparitor is 2.238" at 0.015" off the lands. I find that the COAL is not really that valuable as the length can vary between bullets considerably.

 

[memilanuk]

I find that the COAL is not really that valuable as the length can vary between bullets considerably.

In an absolute sense, you are correct. But given the differences between comparators - whether the hole is radiuses, tapered, etc. Also, I've found some claims of 0.nnn" freebore to be rather... suspect, at best. And depending on the method used, terms such as 'jam' or 'jump', and how much, can be highly subjective.

As such, COAL *can* be useful for comparison purposes, as even with the innate variation in the OAL of the bullet itself, it may be the least variable comparison. I wouldn't take someone else's load at a particular OAL and go forth and run with it (*maybe* if it was mag length and I knew that wasn't going to jam anything in my particular chamber...) but its the closest way to compare the length of loads using word-of-mouth (or keyboard) information that I've found.

 

[Ned Ludd]

In an absolute sense, you are correct. But given the differences between comparators - whether the hole is radiuses, tapered, etc. Also, I've found some claims of 0.nnn" freebore to be rather... suspect, at best. And depending on the method used, terms such as 'jam' or 'jump', and how much, can be highly subjective.

As such, COAL *can* be useful for comparison purposes, as even with the innate variation in the OAL of the bullet itself, it may be the least variable comparison. I wouldn't take someone else's load at a particular OAL and go forth and run with it (*maybe* if it was mag length and I knew that wasn't going to jam anything in my particular chamber...) but its the closest way to compare the length of loads using word-of-mouth (or keyboard) information that I've found.

As Monte described, COAL has its uses. I point bullets, and as a first step for that process, I find it expedient to sort bullets by OAL into groups of ~ .0015" so that I can obtain uniform pointing for as many bullets as I need from a single length group without having to reset the pointing die micrometer. For that reason, I know to within less than +/- .001" the length of a specific bullet, simply by the length group from which it came. The usefulness of that comes into play if you're using QuickLoad as a means to expedite load development, which I do. If you know the length of your bullets to some degree of accuracy, COAL, which is the critical cartridge length input used by QuickLoad, is essential for getting back the best predictive information from the program.

One of the rifles for which I have loaded 185 Juggernauts over Varget for a number of years was chambered with 0.085" freebore. It is very close to the short end for Juggernauts, but you can still seat them at .020" to .025" off the lands while keeping the boattail/bearing surface junction above the neck/shoulder junction. With several different 30" barrels, this rifle consistently tunes in at ~2720 fps with standard Lapua .308 brass. The predicted pressure (QL) runs in the neighborhood of 60K psi, and I've found that unless you're using Lapua Palma brass, loads predicted to run much over 62K will suffer from poor brass life. I have another .308 Win F-TR rifle that has a much longer freebore (.180") for which I have also loaded both 185 Juggernauts and 185 Hybrids for some time. Frankly, that freebore is much longer than I would choose for 185 Juggernauts, but you can certainly load them, albeit seated much farther out in the neck than with the previous rifle I mentioned. In this rifle, the Juggernauts tune in at around 2770 fps, largely due to the greater case volume, which allows you to get a bit more velocity at the same pressure. Depending on the specific Lot of Varget, loads with both of these rifles have fallen in the ~ 43.3 to 43.9 gr range to generate the velocities and predicted pressures listed above.

The idea in F-Class is to develop a load that shoots reasonably well, meaning a quarter to half MOA for 5-shot groups at 100 yd, that will maintain its combustion characteristics, and therefore velocity and pressure, over the long strings (20+ shots) we typically fire in F-Class matches. It is a different approach than you will usually find for a BR load, because the major sources of error (shot dispersion) are not all the same. Given the amount of heat generated in a barrel during 20+ strings, it is critical in F-Class to have a load that is minimally sensitive to temperature-induced velocity changes. A significant portion of the powder burns in the first 6-10 inches of barrel, and when the barrel gets screaming hot well into a long string of fire, you don't want to observe huge velocity changes relative to earlier shots in the string, or between strings as the temperature changes during the course of the day/match. Finding a minimal ES/SD window with respect to charge weight means the velocity is changing the least with respect to changing charge weight. By analogy, this is the same window in which thermal variation in powder burn rate will also have a minimal impact.

In addition, it usually takes anywhere from 5-6 minutes, to as long as 15-20+ minutes to complete a 20-shot string with sighters. Wind changes during that time period are by far the greatest source of dropped points in a typical F-Class match. It is simply not possible in F-Class to put 5-shots down range for a group in 30 seconds with (hopefully) fairly consistent wind conditions like you might see in BR, because target/pit service simply isn't ever going to be that fast. So a typical F-Class load should be focused primarily on extreme consistency during the time frame of a typical string of fire, as opposed to absolute extreme precision. Good precision yes, but maybe not the absolute best precision, if that comes at the cost of lesser consistency over long strings of fire. For these reasons, minimization of ES/SD is more important than it might be in some other disciplines. So you start by finding your optimal charge weight where the burn characteristics of the load produce minimal velocity variation. In my hands, this most often corresponds to the best grouping at 100 yd, but not always. It is generally possible to tune in the groups' spread afterward with appropriate seating depth testing, regardless of whether or not the groups initially corresponding to the optimal charge weight window were the smallest. The key to both of these steps in the load development process is that you need to use sufficiently fine increments to effectively define the boundaries of the optimal windows, whether seating depth or charge weight, so you can load close to the middle (charge weight) or close to the longest (seating depth).

Given your setup, I would be willing to bet that if you test from about 42.8 to 43.8/44.0 gr in 0.2 gr increments with the bullets seated at .015" off, you will find a window of (at least) a couple increments wide that exhibits minimized ES/SD. This is a characteristic behavior of optimal combustion specifically for the load you're trying to develop. It is dependent on the powder burn rate, optimal case fill ratio, bullet weight, and likely a few other parameters. Once you have this information, I'd go back and test seating depth in .003" increments from about .010" off to .030" off. I believe if you do the finer increment optimization you will end up with a load that exhibits good precision and will maintain it over a long string of fire, which will be well worth the extra effort over the long run.

 

[Bart B.]

Benchmark used a SAAMI Match grade reamer. It produced a 0.110" Freebore. I loaded a Berger 200.20X long in a dummy round for Benchmark. They used it to test the Freebore. The end result, was that when the dummy was chambered it seated the round an additional 0.004".

Where does SAAMI list its 308 Match grade chamber specs?

Their only 308 Win chamber drawing I've seen shows a .090" long freebore and a 1.75 degree throat. If the match freebore is .110" and other dimensions don't change, that adds .020" to bullet jump.

Most 308 Win barrel throats advance .0010" every few dozen rounds. Varies a little with bullet ogive shape.

Bore erosion gauges for M1 and M14 service rifles go into their limit about .0001" per shot. Their gauge head taper is .010" per inch

 

[jsthntn247]

Load a string or 2 at 43.0 and 15 off and 20 off and go shoot a match. I don't do load dev until I have 200 rounds on the barrel for the reason your seeing.

 

[David Christian]

I have been working to refine my load. Here is what I am shooting:

Caliber: .308
Case: Lapua Winchester
Primer: CCI BR-2
Bullet: Berger 185gr Juggernaut
Powder: Hodgdon Varget

I had a load development starting at 41.0gr to 44.5gr. I seated the bullet 0.015" off the lands (OTL) and ended up at 43.5gr of powder producing 2750fps.

I have shot this at a 500 yard match and was not overly impressed by the outcome. Expected better. So I worked up three loads 43.0gr, 43.5gr and 44.0gr and seated three round starting at 0.010" OTL to 0.030" in 0.005" increments. Went to the range and set up the target at 100 yards. Conditions were overcast, misty but very light breeze.

Here is my results:

View attachment 1036978

It appears that 43.0gr seated at 0.015" OTL seems to be the best. I say seems to be because when I did the first load development to come up with a powder load, one of the loads that didn't perform was 43.0gr and I had seated those at 0.015" off the lands. One difference was at that time I did the initial load development I had a brand new barrel from Benchmark with only a few rounds down the pipe. Now that I have put 174 rounds down her and that could have made the difference.
Does this sound logical?

I just learned the same lesson. My new barrel was still speeding up during the first 200 rounds. I had to go back and repeat all of my testing. My new load is a few .1 grains less than orignially tested. I won’t make that mistake again and will wait until I have 200 rounds down the barrel before fine tuning the load.

 

[Red Dawg 34]

I have been working to refine my load. Here is what I am shooting:

Caliber: .308
Case: Lapua Winchester
Primer: CCI BR-2
Bullet: Berger 185gr Juggernaut
Powder: Hodgdon Varget

I had a load development starting at 41.0gr to 44.5gr. I seated the bullet 0.015" off the lands (OTL) and ended up at 43.5gr of powder producing 2750fps.

I have shot this at a 500 yard match and was not overly impressed by the outcome. Expected better. So I worked up three loads 43.0gr, 43.5gr and 44.0gr and seated three round starting at 0.010" OTL to 0.030" in 0.005" increments. Went to the range and set up the target at 100 yards. Conditions were overcast, misty but very light breeze.

Here is my results:

View attachment 1036978

It appears that 43.0gr seated at 0.015" OTL seems to be the best. I say seems to be because when I did the first load development to come up with a powder load, one of the loads that didn't perform was 43.0gr and I had seated those at 0.015" off the lands. One difference was at that time I did the initial load development I had a brand new barrel from Benchmark with only a few rounds down the pipe. Now that I have put 174 rounds down her and that could have made the difference.
Does this sound logical?

Looks like you are close. I used to shoot 185 jugs out of a defiance action with a heavy Palma contoured Hawk Hill barrel cut to 29 inches. The low and best node was 42.8 of Varget @ 22,000ths off the lands. Might be worth looking at if your rifle is similar.