Interesting ...very technical

Works for me. The caveat being: sometimes between the little things like case volume variation and hot/cold lots of powder, primers, etc. it may not seem to be 'right on' every time. Usually a little constructive tinkering w/ the numbers to fudge the computer model to fit reality and soon enough, I can dialed in pretty good. Keep in mind, my goal is not necessarily groups in the 'zeroes' or even the 'ones' for short range benchrest, so your mileage may vary.
 
it was nice to see someone else acknowledge adjusting the data in quickload to generate data that relexs real life data.

i measure the vol of my weight sorted cases and add to the data base by lot.
make notes of the ba adjustment for my powder vs the powder in quickload.


mike in co
 
Some interesting reading. I have read of the OCW some time back and did some calculations. They were long and tedious but not difficult. I might add that I am not an engineer so I don't have a strong suit in math.

Load development was always a problem for me in that I didn't know which way to go or what to change, charge weight, bullet, seating depth, etc.

Now that I use tuners on my bench guns none of this matters. I know what bullet I am going to use, and the powder, etc. I just change the tuner slightly as the temp increases. Works like a charm. Better than I ever did with changes in powder charges. Long live tuners and those that use them.

Donald
 
Boyd Allen said:
http://www.the-long-family.com/optimal barrel time.htm

Reactions?
Click to expand...

I think this theory has some holes in it.

First, the author contends that barrel bending modes cannot explain dispersion. For the example cited of a 50 fps change from 2900 fps (about 1.7%) in bullet exit velocity causing a large change in dispersion, any phenomenon that caused muzzle exit direction and/or transverse muzzle velocity (the velocity of the barrel at its muzzle) significantly in a time corresponding to the change in time that the bullet spends in the barrel (approximately 1.7% of the 1.24 ms cited, which is 0.021 ms) could cause such a change. One half a cycle would be ideal (a frequency of about 24000 Hz), but any slower frequency would work, particularly with increased amplitude (exactly what happens in a barrel – amplitude is largest for the lower harmonics). VarmitAl’s FEA results show this well – clearly bending modes can cause a change in dispersion in groups of shots with different mean barrel exit times.

Second, we are asked to believe that a bore diameter change makes a difference in bullet exit angle. The wave propagation cited causes a symmetrical change in bore diameter, not an asymmetrical one. The influence on exit angle of a symmetrical change would have to be caused by some secondary asymmetry, for instance, tipping of the bullet in a loose bore. The relatively large 0.00025” peak to peak spike might allow this, but the calculated change from sweet spot to sweet spot is only about 0.000005” (Fig. 5), making this hypothesized chain of events not very convincing.

Third, the magnitude of the variation in muzzle diameter is critical to this theory, even accepting that a symmetrical wave can cause asymmetrical effects on the bullet path. In Fig. 4, it appears that the variation is based on an impulse (infinitely short duration) of pressure, rather than the actual chamber pressure curve. Thus, it seems questionable whether the peak change calculated, 0.00025”, is accurate. With the smoother actual pressure, it is likely to be less, and might be so small as to preclude any significant influence on the bullet.

Fourth, the variation of bullet exit velocity within a group, and its influence on vertical dispersion, is not considered. The authors contend that the sweet spots are when the rate of change of bore diameter is small. If variation in bullet velocity is considered, however, minimum vertical dispersion would result when the changing bore diameter compensated in some way for the differences in bullet velocity within the group. For instance, squeezing the faster bullet to slow it down before it exits the muzzle, and reducing squeeze on the slower bullet, would tend to reduce variation in bullet exit velocity and reduce vertical dispersion. In this example, the sweet spot would be when the muzzle bore diameter is increasing.

Fifth, if a slightly tighter muzzle bore enhances accuracy, as some claim, then the sweet spot, for overall dispersion and in particular horizontal dispersion, would be when the bore is small. Together with the example from the fourth point above, the ultimate sweet spot would be where the bore is small AND increasing (at about 1.16 ms in Fig.. 5).

Anyway, interesting theory, but I am skeptical.
 
It is all too easy - -

to buy into any set of theorys once they become complex and the results seem to make sense. I tend to be skeptical of these kind of things. While some use published research as their basis of explaining why they believe the way they do I tend to cheer on folks who keep trying to make the process easier to deal with. There are so many variables that one can be way down the river in the wrong direction and not know it.

Inovation trumps data, every time.
 
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