In doing some online research of other loads I found a fair amount of folks using N310 and Alliant E3
So as a relatively uneducated reloader what would make N310 suitable for 40 and Titewad not suitable? What other factors are involved beside the speed of the powder?
There is ZERO published data for .40 S&W for N310, e3, or Titewad. All three of those powders are inappropriate for .40S&W according to the manufacturers. So why does Titewad have the bad reputation? N310 is a marketed as a pistol powder and people just LOVE shooting it against the manufacturer's recommendations while chasing
fool's gold low felt recoil. Now, e3 is marketed as shotgun powder, and if you called and asked, they would tell you shotgun only, but people started experimenting with it during the shortage, and people liked it a lot for .40 and 9mm. With Titewad, Hodgdon didn't just market it as shotgun only -- they actually went out of their way to say it wasn't to be used for pistol. That it was too fast and dangerous for pistol. THEN, during the shortage, they developed and published pistol data for Titewad for 9mm. Go figure.
So perhaps one of the reasons people think Titewad is too fast and the other two aren't probably has something to do with Hodgdon characterizing Titewad the way they did. But in reality, all three are ill-advised for .40 S&W. And all three have blown up guns. Guns kaboom every weekend around the country. Going against manufacturer recommendations is one of the contributing factors.
As to your burn rate question/assumption--
Burn rate doesn't mean what you think it means, or at least it's not as clear a measurement as we tend to think of it.
First, what we call burn rate can be controlled by the manufacturer with the primary compound itself, by additives and coatings, or by the shape and size the individual powder particles. Generally speaking, the fatter the particle is, the lower the surface area to mass ratio, and the slower the burn. Sometimes manufacturers will use the exact same powder formula, but have different powders of different burn rates in a series, just by changing the size of the particle. You can see this in the Vihtavuori N300 series, where N310, 320, 330, 340, and 350 have similarly barrel-shaped particles that get bigger and bigger (and burn slower and slower) each step up the product line.
But then there's how "burn rate" plays out, and here's where it gets fruity. Every variable that affects pressure affects burn rate. Smokeless powder burns faster the more pressure it's under, and the faster it burns, the faster it builds pressure, so it's a positive feedback loop. Pressure affects burn rate, which affects pressure, which affects burn rate. This simple fact, combined with different case volumes of different calibers and how case volume affects pressure, means that burn rates will vary from caliber to caliber, and because different powders are affected differently by changes to case volume, they won't vary from caliber to caliber in the same way. Then there are the other variables that change things even within a given caliber. OAL is similar to caliber and case volume, where the shorter the OAL with a given bullet, the smaller the leftover case volume for the powder to occupy, which is the initial combustion chamber. The initial size of the combustion chamber affects pressure. How far the bullet is away from the rifling (up to and including when the bullet is outright jammed into the rifling) affects pressure. How well the bullet obturates (fills in the grooves in the rifling, blocking gas from passing by) affects pressure. Temperature affects pressure. The friction coefficient between the bullet and barrel affects pressure. All sorts of things can affect pressure.
So here's the deal -- those different variables all affect different powders in different ways and to different degrees, especially so with the significant differences you get in case volume between different calibers. So Powder X might have a faster burn rate than Powder Y in 9mm Luger and .40 S&W, but a slower burn rate than Powder Y in .38 Special and .45 ACP. So in that case, how do you determine which is faster when piecing a burn rate chart together? Now factor in all the other variables. The only thing they can do is make a judgment call in each case and give us an inherently inaccurate burn rate chart. One company might say, "Well, we're going to simply take averages and however comes out, it comes out." Another company might say "Well, when making our determinations, let's give the calibers and/or bullets we expect the powder to be used with most often more weight in the calculations." And then some lawyer says "Yeah, but even though our Powder Z falls right in line with Hodgdon's Powder Y with most calibers, Powder Y is a popular powder for 9mm, and our Powder Z was extremely spiky and possibly dangerous with 9mm, so I really do NOT want it right next to Hodgdon's Powder Y on the chart where people might think it's also good for 9mm, and I think we should arbitrarily bump it up to a faster spot."
And that's just with two powders. Imagine having to place 200 powders in order.
And, thus, nobody's burn rate chart is the same as anyone else's.
So when you ask, why are Powder X and Powder Y good for .40 while Powder Z, which appears to be the same in burn rate, is not good for .40 -- the answer is probably that Powder Z tested poorly with .40 because of some consistent physics and/or magic, and the manufacturer is trying to protect you.
And to reiterate an earlier statement, that's not what's going on here because ALL THREE of those powders are deemed inappropriate for .40 by their manufacturers.
All that said -- don't chase the superfast powders for their lower felt recoil. It's a joke. NO ONE will improve going from N320 to N310. Not one bit. Recoil management comes from grip and stance. The kind of recoil differences people chase opting for those superfast powders over one teir up fast powders are utterly inconsequential if your grip and stance are good. And if you're grip and stance aren't good, nothing else is going to help. Get a good fast powder where the manufacturer actually recommends it for your caliber, and work up a load.
Consider Alliant Sport Pistol. It's new, I've heard nothing but excellent reviews, and the published load data puts it right in the sweet spot for both 9mm minor and .40 major. You could be the first kid on your block with the new hotness.
