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#1183
Tony Graham
Participant

Here is Scott Fletcher’s load development:
“I am no 240 expert. However, based on my recent tinkering with 240’s and last weekend’s 1000 yd LG match results (3.823/50; 4.115/49; 2 shoot-off wins), I offer the following comments:

The PA bunch probably has the best collective wisdom on the 240’s. Their concensus is a 10 twist barrel w/ sweet-spot velocities on the order of 2750, with bullets not greater than 0.010 into the lands. This info was the basis for my starting points. I tend to be somewhat adventuresome with my barrel twists and chose a 10-1/2. (an 11 “works” here in the south, but may not in the colder temps of yankeeland). I drive the 240’s @ about 2850, so the rpm’s at this 10-1/2 twist and velocity are comparable to the rpm’s w/ a 10 twist @ 2750 (195k vs 198k). If you want to consider 230’s as well, it is safer to try a 10 twist, as this twist is what Berger recommends.

In my view, BC and velocity are no more than sidebar issues. The real issue is accuracy. The poster-child example of this concept is the Sierra 200 SMK. About a decade ago, Sierra produced a lot of 200’s that were world-beaters. Folks shooting 210’s, 220’s, and 240’s had serious trouble competing with folks shooting the 200 SMK’s because these bullets were simply more accurate, BC and velocity be damned. For the longest time I was a “one trick pony” with my high BC and (only) “fair” accuracy 300 SMK’s driven at 2975. On a ballistics spreadsheet, this should have been an unbeatable combination. However, folks shooting lower BC 210’s at approximately the same velocity were customarily cleaning my clock.

Your system will tell you which bullet it prefers. Barrels fall in love with certain bullets, tolerate some, and barf on others. If you are fortunate to have a barrel that likes both 240’s and 230’s, by all means go with the higher BC 230’s.

What do I mean by a barrel “liking” a bullet? If I’m not shooting 5-shot groups in the 4’s @ 200 yds, I’m looking at other options. That kind of performance from your system says that you should be consistently competitive at 1000 yds if you do your job correctly.

I would suggest ordering 100 of each bullet and putting them through the following screening test, bullets taken directly from the box with no sorting:

First determine the maximum powder charge for the powder/primer combo you have selected. This should be done with all bullets seated 0.010 into the lands. You determine the maximum powder charge by loading cases in 0.5 grain increments, then measuring the extractor groove diameter for each shot. The maximum powder charge is the one that produces a 0.002 inch or greater increase in the extractor groove diameter compared to unshot (virgin) brass. The powder charge that you want to use for the following screening sequence is the one that is 0.5 grains less than the previously defined manximum powder charge.

Shoot 2-shot “groups” @ 200 yds with the 0.5 grain, less-than-maximum powder charge at the following seating depths: 0 (touching), 0.001. 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, and 0.010 into the lands. Select the best 2-shot groups for 5-shot group confirmation testing. The selected 2 shots should be touching, or nearly so. If any of the 5-shot groups tend to string vertical, shoot subsequent confirmatory 5-shot groups @ 0.1 grain increments up to the maximum powder charge in an effort to “knot-up” the group. If none of your 2-shot groups fall on top of/next to each other, your barrel has likely barfed on the bullet.

Do this screening sequence for both the 240’s and the 230’s. You should know real quick what the system likes, merely tolerates, or barfs on. If you are determined to “make” a particular bullet shoot in your system, there are means and methods far beyond this post that can be tried. Sometimes these approaches work, but you will have typically accumulated an elevated round count that has significantly eaten into your useful barrel life.

The foregoing assumes that the Bergers also like seating depths into the lands. I am lead to believe that most hybrid/VLD Bergers do, but a good percentage of the NC “Ackley Boys” shot 210’s from 0.010 to 0.030 off the lands. If Waverly gets plugged back into this thread, he could chime in with where his system likes the 230’s, and the screening test could be adjusted accordingly.

Once you select a bullet, I would suggest sorting all by bearing length and weight. No matter how good the bullet lot appears to be, I have always found a few BAD outliers mixed in, either bearing length, weight, or both. In the case of the 240’s, I think Waverly is dead on by sorting them by “diameter” with a neck sizing bushing. Measuring the diameter of a 240 with a micrometer is not a pleasant experience, as you never get the same reading twice. Not only that, the lot I have has an inferred 0.006 inch variation in diameter. A very competent machinist/1000 yd benchrester who has “cyphered” on his batch of 240’s also maintains that these bullets also can have a banana shape. Sorting bullets over a bushing is a convenient way to cull out both diameter and “banana” extremes. (the 240’s have an exceptionally long bearing length, and the violence/deformations associated with their manufacture probably contribute greatly to these “inconsistencies”)

The foregoing diameter and shape issues should not be considered the “kiss of death” for use (or non-use) of 240 SMK’s. My barrel really likes them at 200 yds right out of the box, diameter and shape variations be damned. The bullet sorting steps that I go through (or anyone goes through, for that matter) are to reduce velocity extreme spread as much as practical. Sorting over a neck sizing bushing is simply another step to this end, paying homage to physical properties we can observe and measure.

It would appear that “all of the above” is workiing for me, based on the collective moaning I heard last weekend.

Hope this has helped and gets you started off on the right foot.

Scott”
From benchrestcentral
Tony