9mm match grade reloading question (it's silly I know)

[Jambo]

This may be a good use of my train time and I know it's a silly question that you seasoned match shooters will roll your eyes at, but....

Why do you reload with heavier bullets for your match grade ammunition? I have seen it for quite some time, and understanding physics with "equal and opposite reaction" it would seem to me that the heavier bullet would result in more felt recoil. Hence this would take your muzzle off target further and mean a longer or more difficult requisition of the target. Obviously this is not correct and I would like to now why before I start buying heads for reloading.

Thanks!!!!!

[vmtcmt]

Sometimes 115gr. 9mm has a hard time knocking steel over. Don't ask how I know.

Also Power Factor is a product of bullet weight and speed. A heavier bullet can be loaded with less powder, and go slower, which balances out recoil. Some guys are toying with 9mm Major PF, which would be tough to make with a light bullet.

[SlowTime]

I find 147 9mm with a fast powder feels softer then 115 grain bullets. The 124 grain bullets are the lightest many will shoot. I have some 160 bullets I haven't tried yet.

Same with 40 S&W loads, 165 feels snappier then 180 grain. I've loaded 200 grain 40 that felt real soft, but was still making around 156pf. I wanted it closer to 135pf and can't wait to feel how it shoots that low as a steel challenge round. But I will bump it up a bit to see how it feels in major PF also.

45acp is opposite for me, with 175 grain feeling the best.

[SRT8]

Power factor is a measure of momentum - it's a direct product of mass * velocity. When you use a lighter bullet, you need more velocity to achieve the same momentum. But the energy required to achieve power factor is greater with the lighter heads because energy = 0.5 * mass * velocity². For example a 147gr head needs a velocity of 850 FPS to achieve a 125PF. A 115gr head needs a velocity 1087 to reach a 125PF. The 147 has an energy of 236 ft lbs, and the 115 has an energy of 302 ft lbs, so the perceived recoil is greater with the 115. This is why heavier bullets tend to feel softer. BUT, there's a lot of other factors that come into to play. Some people prefer the snappier feel of a lighter bullet. Different recoil springs can make a gun track better with the lighter head. In an 9mm major open gun, the lighter bullet allows you to use more powder, which helps to work the comp better.

Now, when it comes to knocking down steel, heavier bullets are generally better, even though they have less energy than a lighter one at the same power factor. Lighter bullets tend to break up more easily when hitting steel and direct that extra energy outward as splatter, where a heavier head tends to stay together better and transfer more energy and momentum to the steel.

That said, I use a 115gr head in my 9mm major open gun running at about 1470 FPS and PF of 169. I like the way it feels better that 124 and it seems the dot tracks better with the lighter head and additional powder. For static steel I'm going to be using a 95gr head running at about 1350 FPS, so hopefully my zero is close to the major load.

[Jambo]

Wow. Thank you very much! After reading this I googled power factor and I am reading up on it more. When I start reloading I will be able to try different loads to see what feels best.

Thanks again!!