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Posted: 8/8/2011 1:25:30 PM EDT
Okay, so I read through this and I still haven't figured the answer out yet.

Let's say I'm looking at Speer GDHPs regular load (i.e., not +P's) in 9mm. What are the differences between 124gr and 147gr? I've looked at the ballistics chart on the Speer webpage, but I'm still not clear as to why I would choose one over the other in my SIG P226 vs. my S&W 6906 vs. my Kahr PM9 etc., or how barrel length (or lack thereof) comes into play.

Any help in laymen's terms is appreciated. Please don't branch out into discussions about +P or +P+ loads –– if you can help me understand this just within the normal loads, I'll figure it out with the higher pressure loads. Many thanks in advance...

Link Posted: 8/9/2011 4:50:58 AM EDT
andy it all really boils down to what weight ammo shoots best or groups best out of your gun. my sig likes 115gn best and i dont shoot +p in anything bullet placement is key. thats why you need to find out what works best for you.good luck.
Link Posted: 8/9/2011 6:23:53 AM EDT
Thanks, I knew that and I will. But I'm also trying to get some basic "scientific understanding" (if you will) of why would I choose a heavier bullet in a particular situation. If I can understand that part of it, then I have an educated platform from where I can begin to tinker and fine-tune.
Link Posted: 8/9/2011 7:35:13 AM EDT
I'm sure someone more knowledgeable will be along to fine tune my rough explanation, but in general, heavier bullets have greater sectional density and tend to penetrate better and more consistently than lighter ones.  Given that we are discussing non +P, in general, a lighter bullet at standard pressure will be moving faster than a heavier bullet (since there is less mass for the powder charge to work on, the bullet will be moving faster than a heavier bullet with the same powder charge.)

As to the different guns/barrel lengths, all rounds will tend to be somewhat slower when fired out of a shorter barrel than if fired from a longer one (though note that Speer does make rounds specifically designed for short barreled weapons.)  I will add that while all rounds lose some velocity when fired out of short barrels, the heavier bullets (say, 147 in 9mm,) tend to lose less velocity both as an absolute figure and as a percentage.  

FWIW, even though you didn't ask for my opinion, I carry 147 Gold Dots or Winchester RA9B in all my 9mms, regardless of barrel length, due to the tendency of those rounds to consistently penetrate adequately, and the negligible (to my eyes) difference in muzzle velocity from one barrel length to another.
Link Posted: 8/9/2011 3:12:19 PM EDT
Penetration is the key.  Pistol bullets poke holes which are rather small, so you need the hole to be as deep as possible in order to maximize your chances of hitting vitals.  Penetration scales more reliably for weight than velocity, that is, a heavy bullet will penetrate deeper and more consistently than a light one.  You're pushing more weight through the same size hole so it makes intuitive sense.

Velocity - at least PISTOL velocities are not high enough to make a difference so +p is probably not going to make a difference.  You really need rifle velocities before it helps, but that's a whole 'nother story.  The difference in velocities between a fast 115 gr load and slow 147 gr load have not been shown to make a difference because you're still way too far under rifle velocities.

FWIW I prefer 147 gr loads in 9mm.
Link Posted: 8/9/2011 4:53:08 PM EDT
I'd shoot the heavyest loads standard pressure. If 9mm 147gr.

Link Posted: 8/11/2011 6:39:42 PM EDT
Thanks for the explanations, keep 'em coming...
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