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Old April 27, 2013, 09:02 AM   #20
Jimro
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Join Date: October 18, 2006
Posts: 5,756
trg42wraglefragle,

Ok, here is the "rest of the story" as Mr. Harvey might say...

Those high BC 155gr bullets have a secant ogive to obtain "VLD" numbers, (Very Low Drag). The traditional tangent ogive isn't as "slippery" in the air, but because of how it interfaces with the rifling in the throat is usually much less picky about seating depth.

Everyone I know who is pushing VLDs is pushing them from a custom chamber. Everyone I know shooting a SAAMI spec chamber is pushing a tangent ogive bullet (175 or 190 Match kings).

For example, a 210 VLD with secant ogive has a better BC than the 220 SMK. So why did Crane NSWC choose the 220 with less velocity as the newest 300 Win Mag sniper bullet? Because of how the bullet performs across the entire range of ballistics. The tangent ogive insures that the bullet will perform well in a variaty of chambers across the DOD, and the heavier bullet goes through the transonic range much better than the VLD.

I realize that you are asking about the 308 Win, but Crane NSWC did the same comparitive testing with the new Mk316 Mod 0 version of M118LR, testing multiple bullets looking for accuracy across multiple platforms (m24, M110, M14/21, etc). They stayed with the 175 because it was the most consistent performer as far as accuracy went.

Anyways, Berger recognized that they had a problem with SAAMI spec chambers and came out with their new "hybrid" ogive, which is secant for the bulk of it and then transitions to tangent before getting to the full diameter body of the bullet. This, in theory, allows the benefits of a VLD for high BC with the benefits of a normal BTHP with regard to not being seating depth sensitive. http://www.accurateshooter.com/balli...ogive-bullets/

I hope this explains why a lot of people are sticking with heavier bullets.

Jimro
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