doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Sherman Bell's pressure testing

This has been referenced many times, so I found the original for posterity. Sorry about the format

Sherman Bell�s pressure testing published in The Double Gun Journal Summer 2002 "Finding Out for Myself, Part VI, Smokeless vs Black", p.19, and summarized in Volume 17: Issue 4, Winter 2006, p. 39


1 1/4 oz. 3 3/4 dram GOEX FFFg Black Powder at 1240 fps and equivalent load Blue Dot
.........................1 inch.................6 inches...............12 inches
BP.......................5900 psi...............4100....................2100
Blue Dot................6000....................4300....................2300

1 1/2 oz. at 1236 fps Blue Dot (weight not stated)
.........................10,000.................4,400...................2000


And the oft cited DuPont mid-1930s pressure curve

For the record: I also am a disciple of the "can't 'splain it but know when I feel it", phase of the moon, voodoo junk science school of shotshell ballistics; possibly related to self treatment of my hopeless flinch with this stuff

So Drew, I hope you can help clarify this. Since pressure = Force / Area, the longer the area along the shotgun barrel that the propellant is dispersed then the lesser the calculated pressure, such as with a slower burning propellant? So Pressure = Mass x Acceleration / Area. So, given the same velocity and payload and since force is the only parameter which relates to recoil, a lower pressure shell really doesen't actually have lesser recoil than a high pressure shell; it only has a lesser perceived recoil because of the character of the 'kick'. Is this correct in your opinion, and does this make any sense? I'm trying to figure out why pressure has nothing to do with recoil. Thanks.

With all the mumbo jumbo from the other post aside, felt recoil to one person might not be the same for the next person shooting the same load, same gun, etc.

It be what it be.

From what I've read and understand a slow burning powder takes longer to reach peak pressure so " felt " recoil will be less. The formula for recoil is : [BwMw+4700Pw}squared/ 64.348Gw
Gw= gun weight in pounds
Bw= weight of ejecta [ shot and wad ] in pounds
Pw= powder weight in pounds
Mv= muzzle velocit
No where is pressure involved. Pressure comes from the burning gas trying to expand against the weight of the wad and shot and the crimp holding it back. Hope this helps - Paul

JWD - yes. Because the shooter is holding the gun, he becomes part of the equation. His weight, build, and height will make a difference to the resistance of the gun going rearward. My small wife looks like a " bobble head " and claims she doesn't feel the recoil. I'm 6' 4" and weigh 235 and do.

In rifles the bullet is touching the rifling and this causes a resistance. In shotgun shells the only resistance is the crimp and makes a big difference in how much pressure is developed.

Bladesmith, I just ran your formula against some guns in my stable. Here were the results:

Subject Gun Subject Load Weight of Ejecta (shot and wad, in pounds) Powder Weight (in pounds) Muzzle Velocity (feet per second) Gun Weight (in pounds) Fealt Recoil
J. Lang 12 Bore B&P F2 Subsound 7/8 ounce, 7.5 shot 0.0546875 0.01171875 1100 6.1875 22.1611455
Army Navy 28 Bore Blackpowder Load, 5/8 ounce, 7.5 shot 0.0390625 0.0078125 1100 7.4375 18.42095423
Perazzi MX-8 12 Bore Remington Handicap Load, 1-1/8 ounce, 7.5 shot, 4 dram eq. 0.075 0.015625 1235 8.875 45.80731919
Browning Citori 20 gauge Lightning Winchester AA 2-3/4" Trap loads, #8 shot, 7/8 ounce load, 2.5 dram eq. 0.0546875 0.009765625 1300 6.56 23.85369398

So putting it this way, an ultralight 12 bore London Best shooting 7/8 ounce 2.5" loads has less kick than a modern Citori 20 gauge shooting a modern load.

Interesting finding, huh?

Also of interest, a big bulky beast of a Perazzi trap gun still kicks 2x as hard as a London gun when the Perazzi is shooting a modern 1-1/8 ounce handicap load compared to the London gun shooting a 7/8 ounce vintage load.

Pretty remarkable, isn't it? A really heavy 12 bore still kicks 2x as much as a really light 12 bore? It goes to show that weight of the gun isn't a big factor in the formula, it really comes down to the huge difference between light loads and heavy loads. I doubt as many people would shoot 1-1/8 ounce loads over 7/8 ounce loads if they knew that it was putting about 2x as much wear and tear on their beloved double with each trigger pull.

Bro. Buzz - not ducking an answer, but needed my lunch dose of Finley

As a victim of a State of Missouri public education, here's the non-deep thinking version.

1.Recoil is measured per Paul's formula and http://www.handloads.com/calc/recoil.asp

2. Perceived or 'felt' recoil is almost impossible to define. Good science is reproducible and measurable and there is no 'pain-o-meter' because pain is entirely subjective. One can measure the difference in perceived pain OF an individual but not BETWEEN individuals. One person may rate the recoil of the same shell and gun as a 7 and the next a 4.
And perceived pain is highly variable and dependent on multiple external and internal physiologic factors ie. pain seems worse at night when there are fewer external stimuli. One's assessment of recoil when shooting a record Kudu vs.sighting in the .375 is entirely different. 'Felt' recoil may differ based on too much coffee that morning or too much alcohol the night before, fatigue, sleep (and other human needs ) deprivation, stress, or anxiety. And stock design/gun fit/muzzle jump contribute significantly.

3. 12g loads with more shot/more powder/more fps have BOTH more pressure AND more recoil, but are unrelated.

12 gauge 7/8 oz. at 1280 fps 7.5 pound shotgun = 12.7 ft/lbs of free recoil
12 gauge 1 oz. at 1180 fps, (2 3/4 Dram) 7.5 pound shotgun = 17.3 ft/lbs of free recoil
12 gauge 1 1/8 oz. at 1200 fps, (3 Dram) 7.5 pound shotgun = 23.0 ft/lbs of free recoil

3 Dr. Eq. 1 1/8 oz. Winchester Trap Load at 1,202 fps - 9,600 psi
AA Xtra-Lite 1 oz WAAL12 at 1189 fps - 8000 psi
AA 'Low noise Low recoil' 15/16 oz. at 980 fps - 6,200 psi

4. Loads through a smaller tube have more pressure. A 1/2 ounce .410 load at 1200 fps has a higher pressure than a 7/8 oz. 12g load at 1200 fps; but in a gun with the same weight, much less recoil.

5. Recoil pads absorb foot-pounds of energy and lengthen the duration of recoil, thereby diminshing perceived recoil.

6. The movement of the bolt against the spring in autoloaders does the same thing.

7. Compression of the base wad in the B&P Gordon System hull is suppose to do the same thing.

8. 'Slow burning' powder is suppose to lengthen duration of recoil.

9. Leo probably 'feels' less recoil, and moves alot less in response, than pencil neck geeks like myself. Same force however.



BTW: I frequently flinch trying to 'click' my mouse, but haven't resorted to a "release mouse" yet
"Flinch", "yips" in golfers, and a host of other movement disorders are now classified as a 'Task Specific Dystonia'
http://www.wemove.org/dys/dys_flimb.html
http://www.imakenews.com/wemovenews/e_article000394359.cfm?x=b11,0,w
The problem has ended the careers of some professional golfers and musicians. Aynsley Smith PhD, Director of Sports Pyschology and Sports Medicine Research at the Mayo Clinic, Rochester, and Dr. Charles Adler of the Mayo Clinic, Scottsdale have researched the problem extensively http://www.radiology.medscape.com/viewarticle/411176
Michael Keyes, M.D. discussed the 'Yips' on p. 28 of the Sept. 05' Shotguns Sports

I hope I live long enough to wear out a Perazzi shooting sporting with 1 1/8 oz. loads. If I do I'll buy me another'n. Don't think it's gonna happen.

There are lots of presentations in sporting that 7/8 oz. will break 100% of the time. Heck, MOST side by side tournaments and charity shoots can be straighted with 7/8 oz. loads. But there are some major tournaments that I don't believe can be.

SRH

Stan, an experienced shooter has to evaluate shots to determine whether his bullets will kill the bird. It is the same in a live bird shoot as it is in sporting clays. Bring some big stuff just in case. I we are shooting soft birds, we shoot soft shells. I'm sorry that my friends got trapped into participating in this BS. OH, here I am participating, but I hope this is the end.

'BS'. Pardon me, but I am having trouble understanding why the discussion of pressure and how it may or may not relate to recoil is classified as BS. Drew, thank you for your articulate explanation. You are always willing to share your knowledge with those of us less informed. Appreciate the time you took to explain what seems to be a fairly complex and somewhat confusing topic, at least for me.

If I promise to delete the BS comment, will you translate the Rookhawk post for those of us who don't quite get it. Even my friend Drew got sucked in. Sherman made it a bit easier to digest.

A 1 1/8oz charge is 28.6% heavier than a 7/8oz charge, Have absolutely no idea where the 2X factor comes from.
Just to muddy the waters a bit remember the entire travel of the load from a standing start to exit from the muzzle occurs in a bit less than 3/1,000 of a second. Take another look at the DuPont chart Drew posted, the part where the "Fast Powder" is exceeding the "Slow Powder" in its pressure rise is a mere fraction of that already minute fraction of total bbl time. The slower pressure rise of the slow powder is offset to a great extent by its heavier charge weight & the fact it maintains a bit higher pressure down the rest of the bbl. From the other thread on this subject I will add there are no cases where both Red Dot & Blue Dot are suitable for giving the same weigh of shot the same velocities. All powders suitable for shotshells are reasonably "FAST" in the lineup of propellant powders. Powders suitable for giving equal balistics to a given shot weight are not really that different in their burn rates. Some of the most dependable light recoiling loads in existance use fast powder, for the simple reason they will burn cleanly at reduced balistics with a light load of shot, something a Slow Powder cannot always be depended on to do.
Also don't be kidded that the acceleration of the gun exactly folloows the pressure curve, it follows the accleration of the velocity curve. Inertia plays a big part here which tends to smooth things out. Assume that the gun weight is 90 times that of the total ejecta weight, a reasonable number, then while the charge travels 30" (Yes I am aware you will likely never have that "Exact" amount of travel inside the bbl, but near to it) the gun will have traveled 1/3" It will have received the force to overcome its inertia in this short distance & the rest of its movement is After the shot has left the bbl.
For every person & for each gun there is a level they will be comfortable with. For a comfortable load take the total weight of everything that goes out the bbl (Shot, wads & powder). Multiply that by the muzzle velocity & divide by the guns weight. This will give you the recoil "Velocity" of the gun in FPS. Any load which falls within that limit will be comfortable to shoot, those which exceed it will grow increasingly uncomfortable the more they exceed it. The same level will not necessarily apply to a load for firing many rounds in a short time as for firing a few rounds over a more spread out time frame. The recoil velocity of a given gun for any individual though is the absolute most important factor in recoil, everything else is mostly advertizing "HYPE". Don't forget also in doing the calculations all weights have to be consistent, whether you convert it all to grains, ounces or pounds is immaterial as long as you make them all the same.
As an example if you used an ounce of shot, 35 grs of wadding & 20 grains of powder & fired them from a 6lb gun & acheived 1200fps M Velocity you would get a recoil velocity of 14fps. Most people would find this reasonablly comfrotable except for concentrated firing of many rounds.
A phenomenum here is that changing the recoil velocity nearly always has a more pronounced effect than a change of recoil energy. If you increased the load to the point it would produce that same 14fpc R Velocity in an 8lb gun then the R Energy would be increased by 33%, however most people would still find it reasonably comfortable. This would represent recoil energies of about 18 & 24 units of kinetic energy for the 6lb & 8lb guns respectfully. "IF" on the other hand you increased the load in the 6lb gun to the point it acheived that same 24 units of kinetic energy it would seem much more uncomfortable.

Bill,

While I completely agree with that premise, and I do so when hunting, it is counterproductive for me when competing. It is critical for me to be as consistent as humanly possible in every way I can. I want the push against my shoulder to be exactly the same every time I pull the trigger. Anytime I start switching anything in the middle of a round.... chokes, shells or anything else, I am inviting problems into my mental game. If I think 1 oz. loads will break every bird out there on a course, I will use them. If not, I will go with the 1 1/8 oz. loads with the supreme confidence that I am prepared for anything.

SRH

Stan, This sort of goes along with the premise that the least little thing, eg, a change in choke, change in shells, someone talking behind you, the wind pops up, a chg in overcast, a car driving by, a plane overhead, a dog barking, and a plethora of other distractions, will always balk some shooters!

Buzz,
On the recoil thing that Bill BS'd, it was tossed around here as recent as a couple yrs ago. I believe Bill is referring to the debate over the concept of whether a shooter can feel the difference between two loads of the same overall energy, one being low peak pressure and one being high peak pressure.

Yes, I can see that now. Thanks Chuck.

buzz,

Things like the wind changing, cars driving by, planes, dogs, don't faze me. I don't even hear them. I can even shoot fine with a little low db conversation behind me, although that is very rude. But if I start changing chokes for a particular station, or changing loads to suit it I am getting my thoughts away from where they need to be before stepping into the box. It is just counterproductive for me.

I tried shooting a Perazzi of mine at a major shoot a couple Saturdays ago, convincing myself that because that course was in the woods and there were no birds on it over 30 yds., I would need to change choke tubes. Shot the worst score I have shot on a course in years, a total blowout. Went out the next morning with my other MX-8 with fixed .020" chokes and shot a score that was 19 birds over the previous days score, on a course just as difficult!

Yeah, there is a lot more of it in my head than I would like to admit.

SRH

Stan, Instead of saying 'will always balk some shooters' , I should have said 'will sometimes balk ALL shooters'. I had a butterfly fooling around the end of my shotgun barrel the other day, and like a dummy, called for the target anyway......MISS!! It can happen to anybody who shoots. That's my point. :-D. P.S. Sorry for being a bit off topic.