Trapshooters Forum banner

"Fast shells spread more"- do they? (Winston)

11845 Views 72 Replies 27 Participants Last post by  fearlessfain
"Fast shells spread more"- do they?

“The effect of shot speed on pattern width is known by all but properly exploited by but few. When you need just a bit more spread and don’t want to bother with changing chokes, just slipping in the next “speed group” – say substituting “heavy” for “light” – can give you just the edge you need, with the bonus of extra pellet energy at the target that changing chokes won’t accomplish.

But you’d best not try this without regard for the physics involved, as thoughtless changes can be more trouble than benefit. Here’s why: pattern development is dependent on air drag, and that drag is not a simple monotonic function of pellet speed, but rather is a function of the square of the speed. So the effect of pattern-widening is magnified at the upper reaches of pellet velocity. Here is an illustrative figure:

And it’s that huge increase in pattern-width at the right side of the graph that can lead the unthinking claysman into trouble. Trying for that last bit of pellet energy for a 60-yard crosser, he loads up with 1400 FPS and pays twice for his mistake: By the time the pattern gets out there it’s often too spread out to even clip off a “visible piece” and the recoil – which he has suffered for no benefit - will affect his shooting for the rest of the day.”

I pen that last period and lay down my quill, letting my eyes drift back appreciatively over the text. Very good – very good indeed! Beyond just repeating what every reader will agree with, I offer not just scientific causation but even surprising graphical evidence, as well as both support and warning to my readers, which about covers the bases, to my mind. OK, that “instrumental” flourish on the x-axis of the graph might be a bit over the top, but it lends such an air of erudition to the enterprise it’s just too good to pass up. If the response to this article is favorable I may be able to string this out for a couple more issues, dreaming up wad and powder effects, interactions with shot size, whatever comes to mind; you know the drill.

Time again to reflect how good I have it. An evening in my den in front of the fire, building castles in air for yet another shooting publication. My ever-more-grey-muzzled retriever curled at my feet, napping and no doubt dreaming about the day in the field I promised him next month when I will pretend to test a brace of matched Purdeys. How can you beat it?

Admit it – you were well into this before you first began to smell a rat. The first parts are so much like what you read everywhere, hear at every club, I dare say they slipped past your BS detector without raising any alarm whatever. So now backtrack and see how far you have to go to find some fact –

Back 1: the “60-yard crosser” paragraph. Well that was a giveaway, wasn’t it?

Back 2: The graph. Sure, that’s a graph of squared numbers, but is it possible? I hope you don’t think so!

Back 4: This is the support for the graph. If it’s nonsense, so is this.

Back 5, right to the start. Unfortunately, there’s hardly a word of truth in it either. In fact the first 12 words, “The effect of shot speed on pattern width is known by all” are as questionable as any of the other fibs I told.


I’ll bet that every reader knows that when you push shot faster the pattern “opens up.” But what happens when I now ask you “How much?” On the off chance that you have an answer to that, I keep another question in reserve: “How do you know?”

This article will cover an experiment involving shot speed and pattern width. For a limited set of data, it answers those questions which I’ll wager stumped most of you: “How much?” and “How do you know?” Based on data from 10 patterns each from shells measured at 1030, 1130, and 1230 feet per second, it will report some statistically significant differences, and some cases where the “expected” differences failed to appear.

Properly, this is the first test of patterning which should be done, since it answers the question of how well speed has to be controlled in comparing shells, chokes, powders and so on. If a difference is found is it due to the change in components or equipment, or could shot velocity be responsible for the whole finding? Conversely, if no difference if found, is it speed making a change in one direction and “canceling out” a change in the other, thus masking a real effect?

The best experiments make you re-examine your ideas, perhaps even change your mind or behavior. This experiment has led me to put some of my MEC bushings away in favor of bigger-numbered, larger-holed ones. With luck, it may change your outlook as well.


The critical piece of equipment making this experiment possible was the software program “Shotgun-Insight”, an application which reads digital photos of patterns and analyses them, making it possible to read enough patterns to draw reasonable conclusions from them. The rest of the equipment used: pattern paper, a digital camera with flash and tripod, PC and the rest, act only as support for the program. Kaleidagraph software produced the graphs.


A MEC 9000H was used to load once-fired STS hulls with Red Dot – 15.7 grains, 17.7 grains, or 19.7 grains. With the components used, the resulting speeds were about 1030, 1130, and 1230 feet per second, as measured by an inductive chronograph, and the 10-shot standard deviations of all were under 5, which is consistent ammo indeed. The shot is Remington magnum 8’s with a count of about 440 per load as dropped by a 1 1/8 oz. MEC bar. All shot is from the same bag.

On a warm day at Metro Gun Club in Blaine, Minnesota, patterns were produced firing a “factory bigbore” Perazzi which has produced consistent full choke patterns in other experiments. The distance used was 34 yards, in an effort to make more use of the “75% diameter” statistic offered by Shotgun Insight. Ten patterns were shot at each shot-speed.

The digital photos were intentionally overexposed by one stop and a fill-in flash was used; all the resulting JPEG’s were usable.


Here, in bare-bones form, are the results of the test.

Based on averages (mean), the patterns from the 1030 FPS loads were denser in the 0-10 inch and 10-20 inch diameter rings than the others and the 20-30 inch diameter ring was less dense. The innermost-ring differences were not statistically significant (I.E., roughly, they could reasonably attributed to chance) while the others were significant.

Look, even I see this as something of a letdown. Hours of work resulting in 12 numbers only four of which mean anything? I plan to go on with “How much?” and “How do I know?” to show what’s behind those numbers, but in the end, those are the “experimental results.”

Let’s look at the data as it comes in, that is, shot by shot.

Looking at the traces from the top down on the graph, the first, the black line and open squares, shows that the pellet count is stable, pattern-to-pattern.

The green dots, connected by a green line, are the pellet counts in the 10-to-20-inch ring. This count too is quite stable.

Going on down, we meet the red trace, the pellet count in the inner 10 inch circle, and the blue trace, the 20-to-30-inch ring. They are more variable than the others, and in addition, vary inversely, that is, when one goes up the other goes down. When there are few pellets in the center there are more on the edge and visa-versa, while the 10-20 inch ring just tracks along. No, these pellets are not jumping from the inner to the outer rings, it’s just that even when the total number of pellets in a 30-inch pattern is the same, some patterns are more spread out than others. “Spreading out” means some 1-10 drifting into the 10-20 area and, at the same time, 10-20 pellets drifting into the 20-30 area. The sector with the most pellets is the one from 10 to 20 inches, but since it is 3 times the area of the 10 inch circle, the pellet density is only about 2/3 that of the center. Once again, these patterns are “hot in the center” like all the others intended for trap shooting.

So what does a significant difference look like?

The shots have been ordered according to total pellets in 30 inches, increasing left to right. The 1030 patterns are the solid markers and lines; the 1130 are outline markers and dotted lines. We see some real differences here. The 1030 FPS 0-10 and 10-20 rings are more dense, less dense in the 20-30 inch ring. So, in fact, increasing the speed 100 fps with this slow start has widened the pattern, much as opening a choke tries, but mostly fails, to do.

And what do non-significant differences look like?

Here the traces cross and re-cross each other in random ways and are often just the same. In this case, starting from a faster baseline than the first graph, increasing shot speed by 100 FPS did not widen the pattern.

Another way of looking at this is the “75% diameter” statistic. This is a calculated rather than counted datum which predicts a circle diameter which would contain 75% of the shot.

This is the same story as told by the “rings” analysis. The 75% diameter of a 1030 FPS shell is smaller, that is, the pattern is smaller.

Just a couple more things. Could I have gotten these results by other means, specifically “by eye” or “side-by-side inspection” or fewer patterns?

No, and here’s reason 1. There’s too much overlap:

Most of the time most of the rings look about the same across all speeds. You can’t possibly tell more than a couple apart, much less several at once.

And here’s reason 2:

If I’d shot just the first 5 I’d say that 1130 FPS had a hotter center than 1230. If I’d shot just the second 5, I’d say that 1230 had a hotter center than 1130. It’s only by shooting all ten can I see that there’s really no difference between them at all. You need at least 10 patterns to avoid being misled.


Based on this, I’m going to speed up my first-shot-doubles shells to about 1150 FPS from the 1050 FPS range I’ve been using. They are 1-oz. anyway; why not give myself a better chance? I’m going to try Extralites at handicap. Just to see if they are denser – denser enough, that is, to help.

Is the odd effect seen here related to sub-sonic v. super-sonic? Someone here, maybe it was HMB, made a big deal of that in an earlier thread. Could he have been right? Some evening I’ll settle down by the fire with Kyra at my feet and explain it all for you.

Yours in Sport,

  • Like
Reactions: Ravenanme and JACK
Not open for further replies.
1 - 7 of 7 Posts

· Registered
4,172 Posts

Thanks Neil. I do think subsonic vs. supersonic has a big influence in pattern performance. I haven't tested as scientifically as you, but I have noted the following:

For loads that never exceed the speed of sound, even at the muzzle, patterns are much tighter and more uniform. For loads with 3' muzzle velocities ranging from 1150fps to 1350 fps, pattern efficiency increased up to about 1220fps and then decreased from there. Pattern from any load I tested above 1325fps or so were really poor. All were shot from a fixed choke modified barrel. I've never done this test with any other barrel, so 1220 might have been the sweet spot for that barrel. Anecdotally, 1 oz factory STS @1180fps seem to break targets into smaller pieces than factory 1oz Nitro's @ 1290.

Andrew, thanks for that great idea. I would never have thought to count pellets that way.

· Registered
4,172 Posts

Dr. Jones, I believe I can answer some of your questions.

I looked at Neil's data and it pretty much matches mine. I can say with a high degree of certainty that our centers are hotter than theory predicts and represent a "better" long range pattern.

I don't think your chokes have much to do with your results. I've found pretty much the same results with loooong, fixed Superposed chokes, 3" Briley Optima chokes, and at least preliminarily, the 1 3/4" chokes in my new (used) MX-15. I think the difference is more velocity related. You shoot faster loads than my 1150-1200fps loads, and I think that accounts for most of the results. BTW, I've never shot Teague chokes, but word on the street is that they shoot tighter per restriction that the more typical conical parallel chokes do.

I have no way to verify this because there are so many variables, but I am developing a distinct impression that bore diameter plays a big role in determining the distribution of shot in the 30" circle. My Superposed had .721 bores and shot tight centers. My 682 had .732 bores and moved pellets from the center to the 15" and 21.2" rings. My MX-15 has a .740 bore done by Tom Wilkenson. I haven't done any serious patterning yet, but the the few I have done show a remarkably even spread. Preliminarily, I'll attribute this to bore dia., because I find it a minor miracle that he got those dinky little choke tubes with 3/4" conical and 1" parallel sections to pattern well at all. In a month or so I'll have time to do a serious set of patterns. If the data varies from my typical findings I'll let you know.

· Registered
4,172 Posts
Dr. Jones, when I mentioned velocity I meant in general. In the past you have posted data on several "fast" shells that conformed to theory. It is intriguing that your shells through your barrels seem to match your theoretical distribution model, and my shells through my barrels, and presumably Neil's, do not. It's worth a discussion.

I'll buy your choke assertion if you are talking about "style" of choke vs. brand. Several articles by the Technoid at The Shotgun Report prompted several discussions with Mr. Eyster, and subsequent discussions with Mr. Skeets and Mr. Wilkenson. All three agree that the most critical aspect of moving shot out of a dense core is radiusing the forcing cone-barrel and choke taper-parallel section junctions. Mr. Eyster also thinks that helps bring flyers into the 30" circle. So, since you are shooting Teague chokes, you only have one of these junctions instead of two. Perhaps that's a factor.

Another factor may be an artifact of pattern shape vs. range. Mr Brister describes the way a full choke pattern developes as trumpet shaped. Mr. Lowry says exactly the same thing, but discusses it in terms of when the pellets reach free flight. I'm just not interested in any shell that doesn't give me 85+% patterns at target range. So it is possible that measuring this "super full" performance at "short" yardage is presenting an anomaly that really isn't there. Patterning at 42 or 44 or 46 yds. may return results that conform more closely to "theoretical" distribution.

To get the most out of your programs, you have have to have meaningful 75% diameter data. This requires all, or really close to all, of the pellets strikes to be recorded. This requires shooting at shorter range, say 33 or 36 yds and scaling the results to the range you are interested in. I'm convinced that not all the pellets from a tight patterning shell are actually in free flight at these ranges, so the results are skewed. I can say for certain that shooting at 30 yds, running it through SI, then scaling to 40 yds. does not match my paper patterns at 40 yds. Mine are noticably tighter.

I don't think the 20b test will show anything, for several reasons. First, my only 20b is a new field gun with .626 bores. I'm told by several 20b aficionados that mine doesn't follow the rules. Supposedly, it is difficult to get a 20b to pattern well or shoot tight. Secondly, after reading the adverts for ChamberMates and looking at the patterns presented, I decided to experiment. I bought a pair of 28b Little Skeeters from Browning and used them at the Skeet range in a 12b. I didn't get the smoke I get with 1 oz 12b shells, but breaks were convincing and I broke 42 of 50 (IC and Mod chokes).

I agree with you about patterns at shorter yardages. Using your measuring scheme, I like 75% diameters of about 20" at target range, whether it's 16 yds or 45 yds.

I do not agree with Neil's premise concerning fast vs. slow powder. I know many others who can feel the difference in double blind tests, so it is an amazement to me that others cannot.

· Registered
4,172 Posts

Harold, I did one double and several single blind tests. Several others have performed similar tests. I'd call the results anecdotal rather than scientific, because they were informal, with no contols, and all the loads were constructed using powder mfg. loading manuals assuming their velocity readings were correct. None were cronographed to verify.

Double blind: loading Green STS with 17gr new Red Dot and Gold STS with 18 gr Green Dot I dumped all the shells in a bag, selected 2 with my eyes closed and loaded an O/U with 2 shells. I then asked a shooter to fire both at the sky and tell me which kicked more. Yes, yes, I know. The Green Dot has more physical recoil, the chokes were different and the top barrel supposedly kicks more because it is not as in-line with your shoulder. I said you should take this as anecdotal, didn't I? Anyway, about 2/3 of the time the shooters got it right when there were different shells in each chamber.

In single blind tests using 20gr PB, I would tell friends and shooters (known to shoot 1 oz loads @ 1150fps) that I was having trouble with my load, and would they shoot a couple in their gun and tell me what they thought. Anyone who mentioned recoil said it was lower. Since 20 gr of PB has more physical recoil than any other 1 oz load @ 1150 that I know of, the longer recoil pulse of PB vs. the Clays, Red Dot Solo 1000, 700X, etc. that most use has to be attributable to lower felt recoil. If not, how come no one mentioned it kicked more?

A few weeks ago I shot some 1 1/8 ox loads using 15.9 gr TiteGroup (Hodgdon claims 1150fps) and then followed it with a round using 21.5 gr PB (IMR claims 1150 fps). For the very first time I noticed a faster burning powder as having lower perceived recoil than a slower one. The TG was still a sharper jab as opposed to a slower push from PB, but the overall sensation was that TG had less perceived recoil. Since the TG load had 1.18 ft/lb less recoil than the PB load (using identical components other than powder), I'll suppose that that difference outways the longer recoil pulse of PB.

Others have asked me to try different loads for recoil. When I can tell a difference, I always get it right. It just can't be luck.

· Registered
4,172 Posts
"Fast shells spread more"- do they? (Winston)

Neil, the 1/3 who got it wrong mostly said there was no difference. However, some said the Green Dot kicked more. Interestingly, some felt differences when the shells were the same. I used to think that was amusing, but conversations with the powder mfg balliaticians changed my mind. They weight all their test loads and tell me these "identical" loads can vary by as much as 25fps and 2500psi and still be considered acceptable. 25fps is more than enough to affect perceived recoil.

I don't see how any of us could do a real scientific test. It would take forever to carefully weigh each powder and shot charge for as many shells as would be needed to be statically significant. You will have to have special lots of the powders made up so charge weights are identical. You would have to tell the shooter what you were testing for, have them shoot over chonograph screens and make sure no one overheard their remarks. Then you'll need a control group, giving them identical shells to fire, but mislead them by asking them to tell you which one recoils more. All tests would have to be done with the same single barreled, cylinder choked gun. Then you would have to correlate each shot with the chronograph data. Factor in weather conditions, since it would take months to complete this test unless you could set it up at a satellite grand or some other big shoot. You should probably repeat the tests with three different gun weights. How would you account for different physiology? Who has that much time or resources?

That's an awful lot of work to go through for relative results. I'll tell you in advance how it will turn out. Those that key on the time domain (more sensitive to sharp jabs (as opposed to a somewhat more gentle push over a longer distance) will say the fast powder kicks more. Those that equate a farther push with more recoil will think the slow powder kicks more. Those that think 6 of 1, half dozen of the other will say they are the same. You'll get more accurate responses from a lighter gun than a heavier gun.

· Registered
4,172 Posts

It's time to go shooting so I'll keep this short. Yes, patterning shells that produce super full choke results @ 40 yds (85% to 97% PE) at 30 yds and then zooming the scale to 40 yds results in a zoomed pattern that is more open than real life. The reason is the "bell" of the trumpet lies behind the paper at 30 or 33 or 36 yds, so the pattern has not had time to open yet. Your zoom appears to be linear, and you have already said it does not account for a dia/dist pattern curve. At some point your zoom and the real pattern will coincide. After that point, the real pattern will flair more quickly than your zoom will indicate.

When I shoot my next series of patterns I'll move back to a measured 40 yds and not worry about capturing all the pellets. I'll use PE for Pattern Optimizer and add 4%-6%, because that's about how much I think you are off.

BTW, this is only valid for tight chokes and tight patterns. Mod is about the most open choke I can detect any kind of "flair" or "Trumpet" effect, and the effect is small. The more open chokes seem to be linear.
1 - 7 of 7 Posts
Not open for further replies.