.30-338 on the low side

[grizz007]

well in the last 2 days working a max. load in my FN 98 I have figured out that 70 grains of VV N560 averages 2644 fps. with the new Woodleigh .30 240 grain Protected Point. 22" bbl., W-W cases, W-W LRF primers, COL of 3.305". I attempted a few rounds up to 71 and still had room in my case but I was getting some bolt lift.
If I am correct my minimum load would be to go the 10% from max. load which is 63 grains of N560 and a suspected muzzle velocity of 2380 fps. Now these numbers are seemingly correct. What I have a problem with is the fact that this is a magnum and with a 180 TSX I can easily acheive 3000fps. so with this new load with a very heavy bullet just leads me to the thought of a very slow bullet.
Woodleigh expects their new bullet not to exceed 2400fps in order to maintain bullet performance. One other thought I have had is the history of one shot kills being in the 2400-2500fps range, which this would fall into. Probably duplicates the famous 300 H&H but with a heavier bullet and same velocities as its use of the 180 or 200 grain bullets.
Some have compared the .338 magnum to the .30 calibers as rivals in that you have good bullet selection with good SD. I've used the .338's for years and can attest to the fact that penetration is good with this caliber.
Now the question, is this 63 grains of N560 a bit to low for case capacity? Can I expect if I choose to start there a lapse in ignition possibly? I am thinking of using this well within the parameters of the manufacturers specifications. Have you heard of a .30-338 shooting at them low velocities-but hey never with a 240 grain bullet.
Spring Grizz hunt commence shortly and I have pretty much attended to all the little details with all but 2 other exceptions. Ordered a Timney Sportsman trigger w/o safety and need to channel out the wood I have left in foward part of the stock for a accuracy test. Will go ahead and free float and relieve the pressure of that area. Some stated some rifles or Mauser in particular like a bit of pressure up front-not.
Any ideas?
regards
Tim

[Unclenick]

Tim,

Do you have the water capacity of the WW case and the dimensions of the new bullet? If so, I may be able to pop an idea at you. I have been messing with Chris Long's optimum barrel time pressure wave theory for identifying load sweet spots. I can generate a couple suggested sweet spot loads for you based on that information. For water capacity, use a fired case that has NOT been resized (we want the capacity expanded into your particular chamber). Weigh it with the spent primer still in place. Fill with water dead level with the case mouth (no meniscus above or below), weigh again and record the difference. Also your exact barrel length per a rod down the muzzle to the boltface.

I believe you will find you are around 85% full of powder under the bullet at 63 grains. Nowhere near enough space to cause detonation worries, but probably loose enough that you want to try chronographing the load firing a few shots after first tilting muzzle up and a few after first tilting muzzle down before coming to horizontal and firing. This is so the powder is ignited from the two most extreme positions: lying forward and aft. See what average muzzle velocity difference you get in these groups? Lake City M72 match (30-06) is an 85% full case, and it sees about 80 fps difference under these two powder positions. Still accurate, though. Just make sure any difference you get isn't enough to bother you for your purposes. Assuming it doesn't, and you have tweaked the load up and down as needed to find satisfactory accuracy, you should be good to go.

Stock-to-barrel pressure for accuracy should be ideally located at a harmonic node. There is an adjustable tuner you can channel the forestock out to accept. It has a sliding Teflon contact on a lead screw that you tune for best performance. You can still put it in after floating, so start with floating. There is also a method of epoxying-in two diagonal supports about 120° apart under the barrel. You do this with wood shims until you get 10-20 lbs pressure upward. Harold Vaughn credit's O'Conner with this and says it works well. However, I would try shooting an Audette ladder to find a sweet spot load with the floating barrel before making further mechanical modifications.

If you want help guessing a sweet spot load by the numbers, let me know here or drop me a PM with the measurements? Chris Long's optimum barrel time calculator is usually within a couple percent, so it narrows how many charges you need to go through to find the sweet spot.

Nick

[grizz007]

unclenick, you are informative indeed! I have no time at the present but I will either post or pm you shortly-thank you kindly.

regards
Tim

[grizz007]

unclenick,
sent you a pm. we can warm this forum up with your tech specs.

Tim

[Unclenick]

Tim,

Here's a pile of stuff. I just hope it doesn't prove to be the wrong kind of pile.

Background:

Dan Newberry observed that some loads, like the Federal Gold Medal .308 match ammunition with 168 grains Sierra MK, would shoot very accurately in a wide range of guns without special tweaking to suit the gun used. He decided it might be possible to identify an optimal charge weight (OCW) for different cartridges (http://www.clik.to/optimalchargeweight). He found he could. Chris Long decided to work out a theoretical bases for this phenomenon (http://www.the-long-family.com/OBT_paper.htm). Chris makes the salient observation that the usual barrel harmonic models describe harmonic barrel vibratory bending, which changes a group's point of impact (POI) on the axis of the bending motion. This does not explain why groups outside a harmonic sweet spot get bigger in all directions instead of just shifting on the vibration moment?

Chris worked out that muzzle distortion can occur due to an acoustic barrel wave initiated by firing pressure. This wave reflects back and forth along the barrel at the speed of sound in steel; almost mach 17. This wave traverses the barrel several times while the bullet is on its way to the muzzle. At certain periods of time, the complex reflecting wave distorts the muzzle. At others (sweet spots) the muzzle shape is stable. The nifty thing about this is, since the speed of sound in all barrel steels is essentially the same, calculation of the sweet spot timing is dependent on barrel length alone, and not the barrel's weight, profile, or bore diameter, as harmonic vibrations are. Chris posts both his theory and an Excel file for computing bullet barrel times that have the bullet exiting the muzzle at a moment when it is undistorted by the acoustic wave. Since powder burning characteristics affect barrel time, two different powders loaded to produce the same muzzle velocity do not produce the same barrel time. You need a calculator for that, and Chris Long geared his Excel file to work in conjunction with the barrel time calculations produced by the QuickLOAD (http://www.neconos.com/) internal ballistics program.

The only hang-up in Long's theory is that different actions, cartridge lengths, and barrel engagement can alter the effective wave reflecting length of the barrel. Additionally, different powder lots will produce different barrel times than those predicted by QuickLOAD, so, when you work out the nominal loads in QuickLOAD, you typically have about a 2% barrel time error to deal with. This is why you wind up with a range of loads to try.

You provided the following data:

Needed for Chris Long's calculator
Barrel length: 22 1/8 inches

Needed for QuickLOAD
Fired Case Water Capacity: 87 grains
Bullet Length: 1.430 inches
COL: 3.305 inches
Bullet Weight: 240 grains

I forgot to ask for measured bullet weights? However, a 5 grain variance only results in about 0.002 ms change in barrel time, which is about a tenth of the 2% barrel time error, so unless they are terribly far off, it doesn't matter.

From Long's calculator, the barrel's projected sweet spot times include:

1.208 ms
1.323 ms
1.399 ms
1.512 ms

Ranging for the 2% error, these become:

1.184—1.233 ms
1.296—1.349 ms
1.371—1.427 ms
1.482—1.543 ms

You'll notice the error almost connects them, which makes you wonder right off it the whole idea is fiction? There's bound to be a sweet spot in all that charge tolerance, after all. However, what the wide coverage does not explain is that the number of sweet spots is correctly predicted. Also, once you've found one and adjusted the formula for equivalent new barrel length to match, the other spots are correctly located.

When I ran the QuickLOAD Calculator on a 70 grain charge of N560, the predicted muzzle velocity was 2687 fps. You measured 2644 fps. Even though this is out by +1.6%, that is also within the error of most chronometers. The Oehler 35 (no longer available) and CED Millennium (employing its IR screen option) and the PV-21 being the only exceptions I am aware of (about .3% or better accuracy).

QuickLOAD predicted pressure of the 70 grain load to be about 65,500 PSI, just above the cartridge SAMMI max of 64,000 PSI, so this is a hot load, even though it is within the tolerance of your particular rifle. Going to 71 grains pushes the prediction up another 3,100 PSI, to a little over 68,600 PSI, so it is not a surprise pressure signs began showing up there. It wouldn't take much more powder to wind up in proof load territory.

The 70 grain load above produced a barrel time of 1.211 ms in QuickLOAD. This is about the middle of the range for the fastest OBT listed above. However, pressure limitations make it dangerous to seek out a sweet spot in this range, so it is best to drop it. The slowest OBT listed above is produced by around 60 grains of N560, and this predicts about 2300 fps at the muzzle, which is below the velocity range of interest (2400 fps). So, I set about finding the charges at the ends of the middle two ranges. In QuickLOAD these were:

Charge Range 1
Time - Grains N560 - Predicted MV - Predicted Pmax - Case Capacity Used
1.296 ms - 66.85 grains - 2,568 fps - 56,620 PSI - 92.4%
1.349 ms - 65.00 grains - 2,497 fps - 51,967 PSI - 89.8%

Charge Range 2
Time - Grains N560 - Predicted MV - Predicted Pmax - Case Capacity Used
1.371 ms - 64.25 grains - 2,469 fps - 50,260 PSI - 88.8%
1.427 ms - 62.47 grains - 2,400 fps - 46,204 PSI - 86.3%

Without instrumenting the rifle to match QuickLOAD and your powder lot to it more closely, and without knowing the absolute accuracy of your original chronometer reading, this is within the limits of what can be guessed at from the OBT theory. Now the fun part: you get to load and shoot through the ranges. The second range obviously matches closer to where you said you might want to be loading the rifle. If you work in 0.3 grain steps (and OCW ought to be tolerant of at least +/-0.3 grains) Dan Newberry's Round Robin method (http://home.earthlink.net/~dannewberry/dannewberrysoptimalchargeweightloaddevelopment/id1.html) will get you through the range in 24 rounds (3 shots for each load, including both ends). This would be going from 62.3 grains to 64.4 grains (the nearest overlapping range of whole 0.3 grain steps).

The bottom load from the first range and the top load from the second range are so close, you may want to shoot from 62.2 grains through 67 grains (after rounding to the nearest whole 0.3 grain steps). This takes you from one end to the other of both ranges inclusive, and you can see whether you find both OCW centers? If so, you may find one is wider than the other. That one should prove most repeatable under varying weather conditions.

Try the business of tipping the loaded gun to move the powder forward or back before firing. A true OCW load should be tolerant enough that this doesn't cause an accuracy problem, even though you will see velocity shift. That shift will be greatest for charges that leave the most empty space in the case (range 2).

Good luck with it. If you try it out, I am anxious to hear how you fare with it?

Nick

[grizz007]

Nick,

I look foward to performing the "round robin method". I first am awaiting the Timney from Midway before going all out. Anxious really about performing the test with these bullets. MOA @ 300yds. is something else! Mach 17-that is some speed down the barrel and back. If something is needed for a Q. I'll pm you.
Nothing wrong at all about being long-winded, I am that way quite abit and it is a pleasure talking with someone that does as well. Thanks a bunch.

regards.
Tim