Reloading: what an interesting discovery!

Reloading: what an interesting discovery!

This is a discussion on Reloading: what an interesting discovery! within the General Firearm Discussion forums, part of the Related Topics category; I've been busy reloading among many other things and hence my posting absence for a while. I thought when you retired you had more time ...

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    Reloading: what an interesting discovery!

    I've been busy reloading among many other things and hence my posting absence for a while. I thought when you retired you had more time than you know what to do with it all???

    So I've changed my load development procedure and am now seeing SD's less than 10 fps commonly. So that's good - that's one goal achieved. I also get sub-half MOA groups commonly and that's another goal achieved, and moreso, I'm doing this with Hornady 75 gr BTHP-M bullets and Ramshot TAC powder in my ARs.

    What's so good about the Hornady 75 gr BTHP-M is they cost significantly less than 77 gr SMKs, shoot just as accurately, and actually have better velocity/energy retaining ballistics, and they shoot a bit faster. A buddy that I shoot often with, shoots in long range/precision matches. He won one recently and his prize was 50% off any NightForce scope! Anyway, he had mentioned he couldn't get the 75 gr Hornady to work - glad I continued to pursue the effort! It paid off!

    BTW, his gun and reloads are amazing! I challenged him to shoot a dime (wouldn't you know it) at 200 yards. I know that sounds crazy but he dialed in the scope for 200 on orange dots which are the size of dime, and then took aim at the dime. He hit it the first try. Then it was my turn. I was totally unfamiliar with his bolt gun and my first shot just missed to the right at 3:00. Then, he told me to use a 7:00 hold. I did and hit exactly at 7:00. To heck with that, I put the perfect sized dot in the reticle of the NightForce scope he bought with the prize money dead center on the dot and pulled the trigger - hit!

    Then, the next day we tried it again. He got a first shot, one shot hit again and turned the rifle over to me. I shot one time and the dime was gone! 200 yards! But that's far and away from the reloading intent of this thread, so...

    I now use a 3 shot, 10 load routine to test loads. I either go in 0.2 gr or 0.3 gr increments. This time it was 0.2 gr starting at 23.9 gr going up to 25.7 gr, just a 0.1 gr shy of the max load of 25.8 gr. I average the three shots for each load and use that as "the" velocity. I also calculate the extreme spread (ES) and standard deviation (SD).

    So I went to the range and shot the 10 loads (actually 30 rounds - 3 per each charge) and came home thinking there was something wrong with the gun. Maybe it needed a good cleaning or something. But I went ahead and analyzed the results and plotted them out using Excel. The range of loads was enough to reveal something very interesting! It was the gun, but there isn't anything wrong with the gun - it's just showing off its harmonic deviations! Here's a pic of the results from my AR with a Odin Works 18" heavy barrel, intermediate gas system, and GemTech Trek T suppressor.



    I couldn't help but wonder if this was a fluke or would it repeat, and what if I did the "in-between" charges starting with an even powder charge - like 24 gr. Would I see the same results? Well, no, I didn't...



    But, even what we see can have hidden properties. In the first graph, the cycle was clear; I happened to hit the very points that would reveal the characteristics. In the second set the cyclic nature was pretty well gone but my engineering background told me there may be more to this than it appears. For example, what if the even charges lie on the rising and falling slopes of the odd charges? So, I fired up Excel again and combined the two data sets into one graph and guess what! They're back! The cycles that is, and even more prominent!



    There was only one point that was a little off in the composite and that was the accuracy at a charge of 25.4 grs. We need to remember that by the time I shot this particular group, I had already been at the range prior, at 38 and now I'm back at 41. What I'm getting at is that one set may have been shooter drop out. That's where I lose focus and things either fall apart or I realize I'm drifting and regroup. I realized and regrouped. Honestly, if it weren't for that one point that was a little off, I'd think the data had been synthesized! Notice on the composite that all other points are right in line with the cyclic nature of the gun! I mean just WOW as far as the test data goes.

    But what about my claim that the first set hit the points just right and the second set was in between and would not of themselves revealed the cyclic nature? Well, since you asked, I plotted the second set on the composite to see where the data would land with respect to the composite accuracy wave. It's the gray trace in the graph below:



    We should realize that the points must fall on the charge lines, but what is telling here is that the vertical position of the data point(s) fall exactly on the composite accuracy curve! Well except for that one point at 25.4 charge. But even that's a good example of what would have happened all over the graph if the data points of the second set did not support the first - the wave would have become very distorted!

    And, if you can stand one more graph, this is a composite of the two sets for velocity at each charge. You kinda need this to see at what velocities everything happens at:



    Remember the theory that the best accuracy consistency occurs where adjacent velocities tend to be flat? Not true, and I've seen this time after time. Notice the two flat spots in the velocity graph. Compare those "flats" to the composite accuracy at the same charges - simply not where you want to be!

    Most will benefit little from this because most load for accuracy and don't bother with velocity or velocity variation. Sometimes velocity matters, sometimes it doesn't. Still FWIW...

    There is lots of info in the above charts. I think the most prominent is the cyclic nature of the loads. For example, starting with 24.2 grains on the composite chart, we see a repeating nature for accuracy which shows us that barrels, even heavy ones, have harmonics and they significantly affect accuracy. This strongly suggests barrels have accuracy nodes and they occur more often than one might think. If we use too much charge increment steps, we could miss an important accuracy node and the cyclic nature of the barrel accuracy.

    I believe this cyclic curve is solely due to cyclic nature of the barrel harmonics. It is not the loads because they are precisely loaded - double weighed powder, Lapua new cases, Federal GMM primers, each round measured CBTO to within +/-0.001" All are fired one at a time and chambered just before shooting to avoid chamber heating.

    Another interesting feature in the graph - best accuracy does NOT always occur at the lowest standard deviation! OTOH, there are velocities/charges where the best accuracy does occur with the lowest standard deviation (SD). And there are some accuracies that are really good with not so good SDs. You can see this if you go through the composite chart and compare the best accuracies to the best SDs. It's all there: best accuracy at best SD, great accuracy and not so good SD, and poor accuracy with really good SDs. Just a couple:

    The three best SDs, 3.00, 0.58, and 2.89 fps have some of the worst accuracies, respectively, 1.249, 1.428, and 1.26 MOA. Then some of the best accuracies 0.379 and 0.384 MOA have high SDs, respectively, 20.42 and 27.85 fps. And then there's the best of both worlds, great accuracy at low SDs, e.g. 0.4 MOA and 6.81 fps, 0.371 MOA and 8.5 fps, 0.357 MOA 4.94 fps.
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    Wow, lots of work on your reloading, Tangle. Impressive data to be sure. I'm glad you are still pursuing it and making such good progress; was getting a little wonder going about where you were. As always, I enjoy the results of your work; thank you!
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    I just bought a barrel and dies to shoot 6mm Mongoose rounds. I have to form the cases from .223s and adjust the die to fit the barrel headspace. It should be fun getting the first rounds turned out. No published load data for it either, other than the max 6x45 is about mid 6mm Mongoose load. MY first loads will be for fire forming the cases and barrel break in. Fun, fun, fun.

    Glad your reloading has turned in the direction you were seeking. Working up loads ain't easy.
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    Tangle, this is fertile stuff!

    A few questions mixed in with observations. I understand the notion that smaller standard deviations are better or the sake of repeatability, but what I don't see so far is a strong correlation between standard deviation and accuracy, as you noted near the end of your post. Perhaps you could use these latest data and plot the whole ensemble, leaving out charge weight and velocity - that might be revealing.

    Next - as a dynamics guy, I see things that look like sine waves and immediately question "what's the periodicity of that data?" I can't tell you how many times I've ginned up FFTs on data sets using Excel... usually more for amusement than enlightenment, though. I think you're onto something by questioning your barrel's harmonics, but in general for a given bullet, the duration of the bullet's travel down the barrel (pretty closely related to velocity, but affected by powder burn rate) will be the driving influence on downrange accuracy. The impulsive excitation of the barrel from one load to the next won't result in vastly different barrel vibration, but where the muzzle is when the bullet exits will make a difference. Ideally - and this is the idea behind barrel tuners - the bullet exits the barrel when the barrel velocity is at a relative minimum, i.e., at the max or min amplitude of the sine wave. I still think an accelerometer or two on the barrel and a good data recorder would be intensely interesting from the standpoint of load development!

    A side note regarding bullets exiting muzzles. My company makes miniature guidance devices that these days can be used for steering projectiles fired from mortars, howitzers, etc. A young colleague spent a lot of time measuring the shock levels imparted on our device in the projectile as it was fired from whatever cannon was used. Surprisingly, the biggest shock event during the "launch" of the projectile came as the projectile left the barrel. The initial "detonation" of the powder charge was a very low-frequency event and its amplitude was dwarfed in comparison by muzzle exit blast. He's not a shooter, but in talking this over with him, it made me appreciate the effect of a good muzzle crown on our rifles.
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    Quote Originally Posted by gasmitty View Post
    Tangle, this is fertile stuff!

    A few questions mixed in with observations. I understand the notion that smaller standard deviations are better or the sake of repeatability, but what I don't see so far is a strong correlation between standard deviation and accuracy, as you noted near the end of your post. Perhaps you could use these latest data and plot the whole ensemble, leaving out charge weight and velocity - that might be revealing.

    Next - as a dynamics guy, I see things that look like sine waves and immediately question "what's the periodicity of that data?" I can't tell you how many times I've ginned up FFTs on data sets using Excel... usually more for amusement than enlightenment, though. I think you're onto something by questioning your barrel's harmonics, but in general for a given bullet, the duration of the bullet's travel down the barrel (pretty closely related to velocity, but affected by powder burn rate) will be the driving influence on downrange accuracy. The impulsive excitation of the barrel from one load to the next won't result in vastly different barrel vibration, but where the muzzle is when the bullet exits will make a difference. Ideally - and this is the idea behind barrel tuners - the bullet exits the barrel when the barrel velocity is at a relative minimum, i.e., at the max or min amplitude of the sine wave. I still think an accelerometer or two on the barrel and a good data recorder would be intensely interesting from the standpoint of load development!

    A side note regarding bullets exiting muzzles. My company makes miniature guidance devices that these days can be used for steering projectiles fired from mortars, howitzers, etc. A young colleague spent a lot of time measuring the shock levels imparted on our device in the projectile as it was fired from whatever cannon was used. Surprisingly, the biggest shock event during the "launch" of the projectile came as the projectile left the barrel. The initial "detonation" of the powder charge was a very low-frequency event and its amplitude was dwarfed in comparison by muzzle exit blast. He's not a shooter, but in talking this over with him, it made me appreciate the effect of a good muzzle crown on our rifles.
    Right on! Wanna make some replies, but gotta be at the range about 2:00 and have to get some rounds loaded.
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    Quote Originally Posted by gasmitty View Post
    He's not a shooter, but in talking this over with him, it made me appreciate the effect of a good muzzle crown on our rifles.
    On my new barrel, I opted for a recessed target crown rather than the "standard" threaded barrel on ARs. It cost a little extra, but no more and probably less than a nominal muzzle attachment would run. It's my range toy, not a SD tool.
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    Quote Originally Posted by Tangle View Post
    Right on! Wanna make some replies, but gotta be at the range about 2:00 and have to get some rounds loaded.
    Well, that fell through so...

    Quote Originally Posted by gasmitty View Post
    Tangle, this is fertile stuff!

    A few questions mixed in with observations. I understand the notion that smaller standard deviations are better or the sake of repeatability, but what I don't see so far is a strong correlation between standard deviation and accuracy, as you noted near the end of your post. Perhaps you could use these latest data and plot the whole ensemble, leaving out charge weight and velocity - that might be revealing.
    Wow - great observation! And yeah, I noticed that too. Some claim that best accuracy occurs at the best SDs; I wanted to show that isn't true - it can be, but as you noticed, by no means a given.

    For me, SD is of secondary importance because I'm not shooting at long enough ranges for velocity variations to matter a whole lot. At 300 yards an ES of 50 fps would only change the POI (vertically) by 0.96" or 0.3 MOA. Even at my max range of 500 yards, and ES of 50 fps only changes the POI at 500 by 3.15" or 0.6 MOA. However, at 1,000 yards, which most of us, including myself will never shoot at, that same 50 fps ES would change the POI by 19.45 inches or by almost 2 MOA.

    However, what does bother me is that this particular gun seems to be VERY sensitive to the load. I mean working around a charge in a "stable" SD range, say at 25.1 fps with an accuracy of 0.596, a change of 0.1 gr less changes the accuracy by almost double. A change from 25.1 to 0.1 gr more changes the accuracy close to a factor of 3!

    I have considered that the data may be questionable, but the two sets were shot in two different range times and produced supporting results. I don't understand that much sensitivity.

    Quote Originally Posted by gasmitty View Post
    ...Next - as a dynamics guy, I see things that look like sine waves and immediately question "what's the periodicity of that data?"
    Yep, as soon as I finished the composite I started looking at the period. Have not done anything about it yet however - what would you do for that? Thanks!

    Quote Originally Posted by gasmitty View Post
    ...I think you're onto something by questioning your barrel's harmonics, but in general for a given bullet, the duration of the bullet's travel down the barrel (pretty closely related to velocity, but affected by powder burn rate) will be the driving influence on downrange accuracy. The impulsive excitation of the barrel from one load to the next won't result in vastly different barrel vibration, but where the muzzle is when the bullet exits will make a difference.
    Absolutely! Just because the velocity is consistent, doesn't mean it's consistent at the right velocity for accuracy. That's very evident from my graph.

    Quote Originally Posted by gasmitty View Post
    ... Ideally - and this is the idea behind barrel tuners - the bullet exits the barrel when the barrel velocity is at a relative minimum, i.e., at the max or min amplitude of the sine wave.
    Again, absolutely! We think just alike! I've heard the "experts" claim you want to time your bullet to leave the barrel at a node. Not so, we want the bullet to leave the barrel at an anti-node. Or as you very accurately put it, "...at the max or min amplitude of the sine wave..."


    Quote Originally Posted by gasmitty View Post
    ... I still think an accelerometer or two on the barrel and a good data recorder would be intensely interesting from the standpoint of load development!
    Me too, but, LOL, I'm retired now - I don't have time for anything!

    Quote Originally Posted by gasmitty View Post
    ... A side note regarding bullets exiting muzzles. My company makes miniature guidance devices that these days can be used for steering projectiles fired from mortars, howitzers, etc. A young colleague spent a lot of time measuring the shock levels imparted on our device in the projectile as it was fired from whatever cannon was used. Surprisingly, the biggest shock event during the "launch" of the projectile came as the projectile left the barrel. The initial "detonation" of the powder charge was a very low-frequency event and its amplitude was dwarfed in comparison by muzzle exit blast. He's not a shooter, but in talking this over with him, it made me appreciate the effect of a good muzzle crown on our rifles.
    Quite interesting!

    I initially theorized that the powder really doesn't influence accuracy much. But as I thought about it, the impact of the rate of the burning powder could very well change the barrel harmonic magnitude. I don't believe it would change the cyclic rate (frequency) because the barrel is a tube closed on one end. The resonant frequency is set by the length of the barrel alone. E.g. a wind chime is an open tube, but the same principle applies. If you strike it very lightly, it will "ring" at its resonant frequency. If you strike it very hard, it will still ring at its resonant frequency but much louder. I believe the same applies to the powder and gun barrel. While the powder should not change the resonant frequency, it can change the amplitude which will change the POI.

    Great stuff @gasmitty !
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    Quote Originally Posted by OldVet View Post
    I just bought a barrel and dies to shoot 6mm Mongoose rounds. I have to form the cases from .223s and adjust the die to fit the barrel headspace. It should be fun getting the first rounds turned out. No published load data for it either, other than the max 6x45 is about mid 6mm Mongoose load. MY first loads will be for fire forming the cases and barrel break in. Fun, fun, fun.

    Glad your reloading has turned in the direction you were seeking. Working up loads ain't easy.
    @OldVet , Keep me updated on that - that is very interesting! Any more details on how you formed the cases?
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    Quote Originally Posted by Tangle View Post
    @OldVet , Keep me updated on that - that is very interesting! Any more details on how you formed the cases?
    The case "could" be called the 6x45 PO Ackley improved based on the resizing shape. Making the case from .223/5.56 cases is pretty simple. Run one through the Mongoose resizing die and it opens the neck, pushes the shoulder back slightly, and changes the shoulder angle from 30 to 40 degrees. Then the neck is trimmed to 1.690. To finish, the case is fire formed with a mild load to remove most of the case taper and final form the shoulders. If you look at a PO Ackley case, you'll get the idea of how it looks.

    The case is slightly shorter when finished, about 2mm, but because of the reshaped case taper and shoulder, it supposedly gains about 15 grains of volume. The shorter case also allows use of longer bullets than the 6x45, but the longest 100-ish grain bullets will still exceed magazine lengths.

    I've read where some guys cut the front of the nag to allow longer COL but I'm not ready to try that yet. Stainless Steel mags are recommended over ones like Magpul because of some ridge in the front. I haven't checked that out myself, but ordered a couple 5-round and a 10-round mag for this upper.

    I wanted something "different" than .223/5.56, feel unimpressed with 300 BO beyond short range, felt like anyone could buy a 6.5 Grendel off the shelf, but finding barrels and dies in the 6x45 was getting difficult. The Mongoose is a non-SAAMI wildcat (so far), and The headspace of the cases is apparently set with the initial adjustment of the resizing die--adjusting the die so the case fits the chamber.

    One nice thing about it is it uses standard AR-15 parts other than the barrel. No need for a different BCGs, etc.

    Supposed to have better downrange ballistics than the 5.56 and better wind resistance. We'll see about that. I don't have a long range shooting range to verify it nearby.
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    Quote Originally Posted by Tangle View Post
    I've been busy reloading among many other things and hence my posting absence for a while. I thought when you retired you had more time than you know what to do with it all???
    Not really!
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    Quote Originally Posted by OldVet View Post
    I just bought a barrel and dies to shoot 6mm Mongoose rounds. I have to form the cases from .223s and adjust the die to fit the barrel headspace. It should be fun getting the first rounds turned out. No published load data for it either, other than the max 6x45 is about mid 6mm Mongoose load. MY first loads will be for fire forming the cases and barrel break in. Fun, fun, fun.

    Glad your reloading has turned in the direction you were seeking. Working up loads ain't easy.
    I had no idea they had Mongooses in Florida!
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    Quote Originally Posted by G26Raven View Post
    I had no idea they had Mongooses in Florida!
    There will be at least one now. Almost had its first Wolverine.

    Sometimes I just need to feel different.
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    Tangle, remember when you were going crazy hating reloading? Last summer or spring IIRC? When you first started reloading?

    I think you're hooked

    You done good.
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    I initially theorized that the powder really doesn't influence accuracy much. But as I thought about it, the impact of the rate of the burning powder could very well change the barrel harmonic magnitude. I don't believe it would change the cyclic rate (frequency) because the barrel is a tube closed on one end. The resonant frequency is set by the length of the barrel alone. E.g. a wind chime is an open tube, but the same principle applies. If you strike it very lightly, it will "ring" at its resonant frequency. If you strike it very hard, it will still ring at its resonant frequency but much louder. I believe the same applies to the powder and gun barrel. While the powder should not change the resonant frequency, it can change the amplitude which will change the POI.
    The powder charge "detonation" is an impulse and if analyzed in the frequency domain it would appear broadband, probably out to a few kHz. Any barrel mode within that frequency range will be excited. The variation in intensity of the excitation from your min charge to your max is on the order of 25% based on your measured velocities, and that's pretty small (in modal analysis, amplitude ratios are usually viewed on a log scale, and a 1.25 factor is a gnat's whisker). So the variation in barrel response amplitude due to the variation in excitation amplitude will be equally small. Thus for a given powder and bullet weight, charge weight has about a third decimal place effect on barrel vibration amplitude, small enough to be neglected. Find the charge weight that achieves the sweet spot between velocity and best accuracy, and I think you've crossed home plate.
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    Interesting.

    Now for my needs, I shoot out to 900 in a match, so I need that lower SD/ES Combined with accuracy.

    I was fortunate with my 6.5 PRC that I found a load at 54.14gr (that's right - .14) of RL26. I had a low [6/12] - virtually identical SD/ES at 54.1 and 54.2 gr on two different days and ran with it. gives me a little fluff room in powder weighing if my scale drifts or I get in a hurry.

    Holding .5 MOA at 750 yards...including wind drift which was most of it along with an inch off POA in any direction at that range is easy. That load development was a total of less than 60 rounds fired. Even tested with ammo packed in ice for 2.5 hours, packed in what started as boiling water for 2.5 hours, and 60* all in ambient temps in the 50* area. Less than 10 FPS deviation from the ammo at 130* and 17*. I had more deviation from ammo seated .07 deeper for a short COAL mag (30 fps slower).

    Like you though, still fighting to get that perfect Grendel load done up. I have something good for my AR versions, but not great. The Bolt action is proving to be a little more challenging, and i may have to just accept that 123 is about the heaviest you want to run (realized that the gains from 130gr is not that much, and I bought 1k of them). Looking like something in the 115 area would be ideal if they could make one in a .500 BC.

    So, On topic - you have chosen to ignore Litz and load at your accuracy node and ignore the SD and your hit percentage at longer range? What are you going to stick with? Or are you still collecting data points to cook the noodles of us non educated types?
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