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Old 04-12-2011, 05:45   #68
Daryl in Az
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Not really Daryl. Bore dia matters, especially when you are talking small bore vs medium vs large. SD also matters, so does bullet mass, so does bullet counstruction. What I was trying to point out the the OP was his lack of understanding that vel & mass alone don't make up for lack of SD or bullet construction. If you are trying to get anyone to believe the 1mm larger bullet makes up for the lower SD, then you would be wrong, it's been proven many, many times over.
Yes, really; but you missed my point. The smaller diameter bullet only has a higher BC if compared to similar weight bullets in the larger caliber. If you compare, say, 124 grain bullets in 9mm to 155 gr bullets in .40, or 148 grain 9mm to 180 grain .40 of the same type/manufacture, the .40 generally has a higher BC and SD. IOW, medium-weight-for-caliber bullets compared to medium-wieght-for-caliber bullets, or heavy-for-caliber compared to heavy-for-caliber bullets. Apples to apples, so to speak.

Now, if someone's determined to shoot a 124-135 grain bullet for self-defense, and wants to have the highest BC and SD, then the smaller bore makes sense. IME, that would only be the case when addressing a very specific need.

BTW-once a bullet starts to expand, the SD changes. How much depends on how much expansion there is, and what shape the bullet assumes. For that reason, SD pretty much goes out the window, and penetration becomes more dependent on mass and momentum. Bigger and heavier bullets have more momentum, and leave bigger holes.
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