Light and fast vs. Heavy and Slow

Okay this one has been bothering me for a bit now, ran across a couple articles on how a lot of law enforcement agencies have moved their otherwise known heavy grain calibers to ligther grains in the interests of high velocities. One report was of a LEO using a .40 180 grain JHP of some variety that over penetrated and harmed an innocent. After a battery of tests in other calibers and makes they decided on a .40 165 grain JHP +P. As I understand it the extra velocity helped the projectile expand so subsequently lose more momentum inside the perps and thus reduce the chance of an over penetration. While the velocity was greater, the inertia was less because of the reduced weight and surface drag of the better expanded projectile. To me this means that the round did more damage while inside the perp while either not leaving the body or if did leave the body, not with a lot of energy to do any serious harm. The same thing the article said was realized with the .45 ACP.

So if I'm understanding this right, the greater surface area, and lighter weight JHP projectile,while pushed at a high velocity is less likely to overpenetrate than a heavier round JHP because of the heavier rounds momentum.

As I understood it, when it came to SD rounds your choices ought to be light and fast, or heavy and slow. If you wanted a .45 ACP you went with JHPs that were 200-230 grain and didn't go beyond 900fps. If you wanted a .357 magnum you wanted a 125 grain JHP that did at least 1200fps. Granted I shoot Pow R' Ball and light weight high velocity JHPs already but I was just curious if anyone else held the consensus.

And then one that has me going is the reverse. Another poster, Louisianaman, has been kind enough to share his experience with a 200 grain .38 S&W and his findings on penetration which seem quite good.

Does a heavier but slower round put extra pressure on a gun. Would reducing the velocity of a .44 magnum (200 grains at 1200fps) in the interest of a heavier round (350 grains at 900fps) cause a great deal of excess pressure on gun as to harm the gun. It's just bugging me and my Google skill has been lacking on the findings. I know a gentleman who makes his own molds and molds for his friends for casting, I recently got into casting and I want to play around a little with some high grain low velocity loads out of my Ruger SBH .44 magnum. The guy told me he could do a whatever size and weight and wanted(if I was willing to wait a few weeks) in a HPSWC, RNHP, FPHP(flat point hollow point). I've got a couple hundred pounds of lead sitting about and this weekend I plan to make a few loads for the Ruger SBH in 'cowboy' loads.

Okay, dumb question then, how do I calculate the CUP then. Any formulas or online calculators I can use. The idea of heavy projectiles moved at low velocities fascinates me for some reason, might go back to my college days in rugbee.

Will a heavy projectile setup as a HP expand well at low velocities if it's a cast projectile without a jacket. I think this would be viable in a revolver because of a lack of feeding issues.

I was trying to come up with a way to calculate the PSI or CUP of a .44 magnum round that was 400 grains pushed at 600 fps or 900 fps, and a .357 magnum 300 grain pushed at 900 fps and the pressure it would put on a gun. It was really just a self-indulgent interest and the only options it seems is to buy expensive software, there is a Hornady calculator but it won't work on my laptop or desktop for one reason or another.

I was just curious to create a SWCHP or LRNHP that was a really heavy cast round that was slow moving but heavy. In the hopes of creating a low recoil yet punishing SD round. Also the in the .44 magnum, being a .40+ caliber, the round would be a good HD round that while capable of punching human flesh, would not well escape a home. I figured heavy weight would carry the round to the vitals, the HP in the cast lead would lead to expansion, while the velocity would punch the flesh yet cause the round to lose it's momentum quickly and cause the round to 'yaw' inside the human body as the round expanded and should it leave the body, leave with minimal speed and energy incapable of well penetrating walls made up of dry-wall and plywood. Also shold the round go errant, because of it's low speed and heavy weight, it would experience severe drop after twenty yards and hopefully drop compeletely before five hundred yards. Just some self-indulgent ideas.