Adamantium is right on.
Do you have a chronograph? At this point, I think you would be well advised to get one and try to estimate felt recoil with various ammunition (both factory and handloaded) at different bullet weights and velocities with different powders. You will find a WORLD of understanding and enlightenment coming your way.
Interior ballistics (what happens between primer ignition and the bullet exiting the muzzle) is a complex science which no one (not even the experts) truly completely understand (and least of all, me). So take what I am saying with a grain of salt. But this is what I understand, and anyone who can explain where I am mistaken will be sincerely welcomed to correct me.
Smokeless powders do not explode. They burn. How fast depends on the pressure they are under.
Take 10 to 15 grains of smokeless powder in a small pile on a piece of aluminum foil in a campfire pit or something non-flammable and put a match to it. You will get a flame for a second or two that will be about 12-18 inches tall. If that same powder is in a confined space, it will burn MUCH faster. Smokeless powder REQUIRES that pressure (within a narrow band of values) in order to burn at a consistent rate. In a confined space, at the wrong pressures, things can get "spikey" and destroy chambers and ruin your day.
Rate of burn is VITAL to even pressures and even pressures DEPEND on a stable rate of burn. (This is in its own paragraph because it is SO important.)
Pressure spikes can be CATASTROPHIC. Just a little scared? Good. Caution is the watchword. Being just a little scared keeps you double-checking for safety.
You go to slower powders to get more velocity with less recoil than that velocity would normally warrant with a faster powder. Burn time during the entire barrel time at optimal pressure yields the best efficiency whether measured as velocity against pressure or velocity against recoil.
To get lower absolute recoil requires less velocity. Trying to get very much less velocity with a slow powder is dangerous. The performance envelope of slow powders is very narrow. The way to go to safely get less velocity is with a faster powder. Faster powders get up to the proper pressure for consistent burning rate and then quit (presumably when the desired velocity has been reached).
Picking the powder that runs out of burn when the desired velocity is achieved is a trial-and-error business for most of us, but we have a lot of guidance from the load manuals and the burning rate charts. You can get fine tuning by charge weights, but the gross choice of velocities is by powder selection. Use your loading manuals. Extensively.
Having said that, please note that the .40 S&W is a smallish case. That means it is very high efficiency. High efficiency means you get a lot of effect from a small change in cause. That is, a small boost in charge weight produces a big effect in pressure and velocity. Put another way, the .40 is not very forgiving.
This unforgiving nature is not inherently dangerous. It just means that you have to be VERY PRECISE in what you do and to make SMALL CHANGES.
Reloading is not rocket science. But it does involve smoke and fire and things that go very fast, so caution is warranted, lest brain surgery come into play.
Don't be too put off my my scary stories. I just want you to be safe. Do stay within the load recipes and you are safe. They have been extensively tested in ballistics labs. If you do choose to go outside those guidelines, do so after heavily researching and in small increments, paying attention to overpressure signs.
Loading is a delightful avocation. Go for it. Tuning your loads for the performance you want is one of the major advantages of "rolling your own".
Well worth the effort it takes to be safe and intelligent in your quest.
Welcome to the forum and thanks for asking our advice.
Last edited by Lost Sheep; August 31, 2012 at 01:20 AM.