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  • Pressure Testing

    Good article on pressure testing. It takes about 40 hours to test for one caliber and bullet weight with about 16 types of powder.
    Barrels do not last forever.
    If a gage gets a bent piston it can be repaired. If the Piezio gets crushed, they run about $1300 to replace. The Piezio also acts as an emergency blow out plug on way over pressure tests.
    How do they find starting loads? They look at all that has been done in the past and the computer analyses the case for proabable charges.
    There are calibration or check loads that are sent to all loaders so everyome is om the same page.
    Shooting Times is a good magazine for technical information. this issue has loads for .350Legend.

  • #2
    This pressure testing is an interesting process for sure. Another interesting process is the simulation of cartridge design and load components. For several years now, I've been using the "QuickLoad" software program to analyze loads that I use. It comes with simulation data for 1200 cartridges, 250 powders and 2500 bullets. It has been especially useful during these times when powder and bullets are hard to find. Within seconds, I can see a list of the powders that perform well with my cartridge, barrel length, specific bullet and seating depth. It does a good job of approximating the velocities, case filing and pressure of any load you care to try. Since I always start testing loads at about 10% below max charge weight, I can work my way up to max loads safely just like I do with the loads shown in reloading manuals.

    It allows me to validate the simulation by tuning the software to match my actual field test results. Once I do this, I find the projected velocities and pressures to be more precise than the reloading manuals by far. What does that do for me? It lets me choose the best powders without having to actually buy the powder and field test it. It lets me analyze the effect of a specific barrel length on velocity using different powders. It lets me analyze the effect of bullet seating depth on pressure and velocity so that I can safely vary seating depth to improve accuracy. It lets me discover powders that are optimum for several different cartridges I shoot, minimizing the number of powders I stock. Most importantly, it exposes me to 250 powders for a given cartridge while the reloading manuals typically list about 10 and often miss the one that is optimal for that cartridge, given my bullet and barrel length.

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    • #3
      That is an interesting program. I did not know there are that many powders. the only thing the article said they looked at existing similar componentss to get a starting point. Maybe they use the program to. Does the program show an expected curve ?

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      • #4
        The program shows the velocity and pressure curve from ignition until the bullet leaves the muzzle for the load/seating depth you define. If you want to see the changes in these attributes as you add incremental powder or seating depth adjustments, you need to update these attributes manually and plot the resulting velocity/pressure curve yourself. I don't do that too often as I depend on actual field testing to help me isolate optimum loads once I'm within a grain or two of powder.

        I normally start field testing with a .010" or .020" bullet jump using an incremental powder increase until I hit early pressure signs. Then for charges that show a great velocity Standard Deviation, I test incremental seating depths with .002" increments looking for maximum precision/accuracy. QuickLoad also shows the dwell time of the projectile in the barrel at any point in its acceleration so you can use results from QuickLoad in combination with Optimum Barrel Time algorithms to pre-determine optimum accuracy nodes in the barrel's harmonics.

        Although there are 250 powders listed, many of them are literally the same powder branded with a different name by a different distributer. For example Lovex powder is made by Explosia in the Czech Republic. It is in turn marketed in the U.S. The net effect is that we get slight variations from various brands so we might end up with as many as half a dozen powders that are pretty much the same. For example, we have Lovex S062 that is marketed by Shooter's World as "Precision Rifle", by Hodgon as "Varget" and "IMR4320".

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        • #5
          I also think the manufacturer in Austrail9ia and Florida also package powders fir different distributors.
          I have a question on bullet jump I have two Weatherbys and both are capable of clover leafs at 100 yds. Question, how can they achieve that kind of accuracy with so much bullet jump ? I never understood that. I know bench shooters are concerned about jump and one guy I watched at a BR range even marked his brass with a sharpie so he could orient the case in the chamber with the mark up the same way every time. They were shooting several times through the same hole so they had to put up new target backers to prove the shot. This was in the '80's.

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          • #6
            Most bullets are very sensitive to bullet jump. For long range precision, I test bullet seating by incrementing .002" from .000 to .030 from the lands. I have seen that changing the bullet seating depth by as little as .002 may cut the group size in half at 600 yards. This has a slight effect on pressure and velocity and it is enough to move the bullet velocity to being totally harmonic with barrel flexing and torque. In other words, we use this technique to tune our precision load to the specific rifle we are shooting. Rifles are all different based on their barrel length, weight, bore dimensions, twist rate, rifling pattern, type of steel, etc.

            Many long and very pointed VLD bullets using a secant ogive contour have best long range precision when seated right on the lands or even pushed into the lands as much as .010". Doing this not only may provide the highest precision but it may also serve to center the bullet in the bore for a properly balanced bullet engraving. I prefer not to jam bullets into the lands; especially for hunting loads. I can almost guarantee that if you have to unload your rifle and extract one of these cartridges, the bullet will stick hard in the bore. Not only will you have powder granules in your action but you may need a cleaning rod to poke the bullet back out of the barrel.

            A common competition bullet, the "Berger Hybrid" with a combination of the secant and tanget ogive usually does better with a jump in the .010 to .020 range. We also see many bullets doing equally well when seated .065-.075 off the lands. By testing seating depths on your reloads, you may find several depths that provide excellent precision. For example, my .300 Dakota shoots well using Berger 215g hybrid bullets seated .020 from the lands but it shoots equally well when I seat the bullet nearly a quarter of an inch deeper so that the bullet can fit in my magazine for hunting.

            Since you are a Weatherby owner, you probably know that they are known for using long free bores (i.e. "jump") in their chambers. This is the portion of the chamber that lies just ahead of the case mouth and is the same diameter as the bullet; it leads the bullet to the start of the ramp that positions the bullet into the bore. A longer free bore allows longer (i.e. heavier for caliber) bullets to be used without displacing too much powder in the case. It generates higher velocity in most smaller bullets that can't be seated to protrude enough to reach the bore. This long free bore could negatively impact the accuracy of smaller bullets but you need to test them just like all other bullets. I actually don't treat Weatherbys any different though since I measure to determine the maximum cartridge overall length in the chamber (from the bolt face to where the bullet just touches the bore) and then seat the bullet properly in relation to that maximum cartridge overall length. I then use the seating depth that provides the greatest precision. Even the smaller bullets can be tuned to shoot well.

            You can quite easily determine maximum cartridge overall length by:

            1. Close your bolt on a empty chamber and push a cleaning rod from the muzzle end until it rests on the bolt face. Mark the rod with a pencil where the rod exits the muzzle with a pencil.

            2. Remove the bolt, point the rifle down and drop a bullet; nose down into the chamber. Hold the bullet gently in place with something like a pencil.

            3. Gently push the cleaning rod against the tip of the bullet. Mark the rod with the pencil again where it exits the muzzle.

            4. Measure the distance between the two pencil marks on the cleaning rod. This is your maximum cartridge overall length. If you allow the cartridge to be longer than that, you will be forcing the bullet into the bore when you close the bolt on the cartridge.

            You don't have to worry about rocket ship precision. You will be using this value as a baseline number and you will be testing loads with varying offsets from this number. Even if you are not exactly correct with this number, you will still chose the most accurate load you test later.
            Last edited by DakotaMan; 08-03-2021, 05:42 PM.

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            • #7
              I will have to measue the .300 and .340 I have. Do you think roy uses the jump to load a hotter charge ?

              when you order a custom barrel do you specify the free bore ? Is it possible to increase freebore after the fact just using a reamer or taper reamer. ? Similar to a set back ?

              Comment


              • #8
                I suspect Roy probably used the longer free bore to get additional velocity by letting bullets accelerate fast before encountering the bore and keeping big long bullets out of the powder column. With his free bores, we got extra velocity (because of the fast ramp up) at the cost of long range accuracy (due to some loss of bullet concentricity at bore impact). But that was before we had such long VLD bullets.

                Nowadays, we go for longer free bore so the long VLDs seat in the neck of the case. This prevents the long bullet from reducing the cartridge's powder capacity. It also allows reloaders to seat the bullet far enough ahead of the shoulder/neck junction to avoid the brass "doughnut" that often forms inside the case as brass flows forward. Of course we can ream out the brass "doughnut" but with the longer free bore, we don't have to spend the time.

                I occasionally specify the free bore on my precision rifle reamers but that requires a custom reamer development. For example, my new 6mm Dasher has a .130" free bore while the initial Dashers used a .104 free bore. Mine is optimized for a 105g Berger Hybrid bullet or a 107g Sierra Match King to fit in the case above the shoulder/neck junction. Of course we can use free bore reamers to extend the free bore but I prefer to get it right the first time. I am obsessive about getting the whole chamber (including free bore) perfectly aligned with the bore. That is tough to do with just a free bore reamer once the chamber is cut. If your run out is more than .0002" you could suffer long range accuracy problems.
                Last edited by DakotaMan; 08-04-2021, 11:51 PM.

                Comment


                • #9
                  Originally posted by DakotaMan View Post
                  I suspect Roy probably used the longer free bore to get additional velocity by letting bullets accelerate fast before encountering the bore and keeping big long bullets out of the powder column. With his free bores, we got extra velocity (because of the fast ramp up) at the cost of long range accuracy (due to some loss of bullet concentricity at bore impact). But that was before we had such long VLD bullets.

                  Nowadays, we go for longer free bore so the long VLDs seat in the neck of the case. This prevents the long bullet from reducing the cartridge's powder capacity. It also allows reloaders to seat the bullet far enough ahead of the shoulder/neck junction to avoid the brass "doughnut" that often forms inside the case as brass flows forward. Of course we can ream out the brass "doughnut" but with the longer free bore, we don't have to spend the time.

                  I occasionally specify the free bore on my precision rifle reamers but that requires a custom reamer development. For example, my new 6mm Dasher has a .130" free bore while the initial Dashers used a .104 free bore. Mine is optimized for a 105g Berger Hybrid bullet or a 107g Sierra Match King to fit in the case above the shoulder/neck junction. Of course we can use free bore reamers to extend the free bore but I prefer to get it right the first time. I am obsessive about getting the whole chamber (including free bore) perfectly aligned with the bore. That is tough to do with just a free bore reamer once the chamber is cut. If your run out is more than .0002" you could suffer long range accuracy problems.
                  You can squeeze a caliper and get a .0002 variance. In my experience NASA and another mfg. needed those type of tolerances and in the early years could not get it in the U.S. - had to go to Sweeden or Germany. NASA was to the extreme and could weigh a finger print, in the 1980's no less.

                  Comment


                  • #10
                    Jimbo, I use Starrett .0002" gages and won't cut a chamber or throat that is more crooked than that. This is to reduce non-concentric bullet engraving. If the engraving on the bullet is not perfectly concentric (caused by the bullet hitting the bore at an angle greater than .0002"), at high rotation speeds of 250,000 RPM or more, the bullet will wobble at ranges past 250 yards (when the bullet transitions from rotating on the axis of the bore to rotating on its center of mass). We can and do get those tolerances. It just takes a lot of time so it is more a matter of economics rather than science. It takes me anywhere from an hour to 2 1/2 days longer in a rifle build to guarantee that level of precision. I would guess that the majority of gunsmiths don't even know about this let alone take the time to do it unless they specialize in building long range precision rifles and charge a LOT for their time.

                    You ask some interesting questions, jimbo. Sorry, couldn't think of a simple, short answer.

                    Comment


                    • #11
                      Is theere a way to test a bullet balance on the longitudinal axis ? Like physists always said outer space would be a perfect way to manufacture perfectly round lead shot, same for Timken Bearings who were thinking about that in the '70's as possibly being one of the first manufacturers in space.

                      I like the Black Belt Remington pistol ammo has as I cinsider the belt useful in correcting any mis alignment with the bore before the bullet exits the barrel. It also lubricates and cleans as you go.

                      I would like to see a match up between you and Ernie . Should be interesting.

                      Comment

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