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OK, I understand the matter of shot deformation, and I understand that we're pushing ROUND pellets here, but what I'm mostly interested in is the clumping... The shot in the center of the shot column wouldn't be deformed very much would it? In a 12 gauge, that's a large majority of the shot is it not? So what happens to that?

Does the shot pattern EVENLY very widely or does the pattern have increased number of "flyer" pellets while the majority of the payload delivers fairly well to point of aim?

SHOOT the loads on paper. That's the only way you'll find out what your gun does with those loads. Various people here can "predict" or huff 'n puff, but only firing the loads in your gun will tell the tale.

So there's no way to give a general guess at what this situation would do to the pattern of any shotgun?

I don't own the shotgun mentioned, nor do I actually have those shells loaded. What I'm asking is basically the effect of velocity on pattern, all other things being equal.

PD, general opinions have already been posted:

First load crappy pattern/hurting shoulder-bloody nose; second load better pattern/less pain.

JC

I think if those interested search for Dr. Andrew Jones and read his pattern work, they'll learn alot. Jones shows there is always going to be annular rings of pellets surrounding a hot core.
In a general sense, the exponential increase in recoil and stock damage is counterbalanced by poor(thin, unuseable) patterns as speed goes up. Recoil growing by the square of velocity as it were.

We can all guess, problem is no one can predict what will happen in a given shotgun.

At least part of the problem is that "all other things being equal" is seldom true. In your example you changed both the wad and powder, not just the velocity. To isolate the velocity variable, you'd need to use all the same components, just more powder. But, of course, doing that would also change the peak pressure. And while some would argue that peak chamber pressure should have "no" effect on patterning, that's wishful thinking without being able to prove it.

Bottom line; even if you managed to convince yourself there was a patterning difference in your tightly controlled test, odds are someone could produce data showing the exact opposite with other loads in another gun.

At the end of the day, what benefit is there to a "general rule?" Even if you thought you could say with 80% certainty that such and such will happen, is that good enough? If it's really important to know, it should be worth spending a few minutes patterning to find out for sure.

phideaux2003,

It might be helpful to read what Bob Brister had to say on the subject; ("Shotgunning the Art and the Science")
...."This brings up another long-standing idea of shooters which is partly correct and partly untrue, the contention that adding velocity opens patterns and that reducing velocity tightens them. As a rule of thumb this idea is true. But it is not necessarily the velocity that makes the difference, it is the shot deformation. If shot are sufficiently hard to resist deformation at the higher pressures of high velocity, then they pattern about as well as the same shot at low velocity. I tested this with the highest velocity loads I have ever put through a gun barrel and with the hardest shot of them all-steel.

Canadian Industries (CIL) made some experimental loads of steel shot several years ago apperently with the intent of increasing penetration by increasing velocity. To be able to do this with reasonable pressures, they loaded a very hot powder charge behind a light load of 1 ounce of shot (12gauge) and obtained velocties said to be over 1,500 feet-per-second. I chronographed them at 1,450 feet-per-second, and thoroughly expected to see blown patterns with such velocity.

Instead those little loads patterned consistently better than 80 percent.

There is undoubtedly a slight pattern-opening effect from extreme velocityeven with steel shot, but it is nothing like that experienced with lead. I tested some high-velocity lead hunting loads containing No. 7 1/2 shot thatwere hard as most hunting loads produced in 1975 and early 76 and got 40-yard patterns around 68 percent from a full choke Perazzi. With the same gun, but the shot replaced by extra-hard, high antimony shot, the pattern jumped to 80 percent. The velocity was still there; the difference had been deformation."
Pete

For a while some sporting clays shooters were using fast 12 gauge Longshot loads at our range. They were exceedingly loud. Burning nearly 40 grains of powder turns up the volume. You would not have to ask what they were shooting. Eventually, people stopped using those loads. Probably, their scores were no better than with milder loads.

About 15 grains Longshot in 28 gauge gives a mild report, so the amount of powder probably makes the difference.