doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Pressure vs recoil in old guns

It should also quite well be noted the 2 3/4" shell was not introduced with the "SuperX" load. In fact drawings fron 1907 found in The L C Smith Plans & specifications book show the 2 3/4" shell as already being standard for their 12ga guns. Virtually all of my post 1900 Lefever's in 12ga also have 2 3/4" chambers. I of course cannot prove they came that way from the factory, but I also have no reason to believe that "Everyone" of them have been re-chambered. In fact the big "Theory" behind the introduction of the SuperX loads was the newly developed Progressive burning powders allowed higher velocities with a heavy shot load "Without" a resultant increase in pressure. Since, as correctly stated, we have no real record of pressure prior to the introduction of SAAMI, I think it totally & absolutely "Self Serving" to infer that all loads on the market prior to that time were "Low Pressure". In fact I do not believe there is a shred of proof the previous 7/8oz, 1200fps 20ga loads the Ithaca Flues had been digesting quite happily had a bit lower pressure than did the new 1oz, 1220fps SX loads which cracked frames. They did however have a heavier "Back-Thrust" to the head of the hull. I am old enough to remember when further powder developments allowed the introduction of the so called "Baby Magnums" in the 50s when standard length shells had their charges increased to 1 1/8 oz in 20ga, 1¼oz in 16ga & 1½oz in 12ga. As these shells were publically stated to develop no higher pressures than had their predecessors many assumed any gun they had been firing with the older SX's were quite suitable for these newer magnums, this was not always the case, but again not because of the higher pressures but the heavier back-thrust. Fortunately we have a readily available formula for comparing this "Back-Thrust, its called recoil. Given the same gun you can bet if a "New Load" kicks harder then not only "You", but also all the parts in the gun which resist the axial loads present from firing the gun are being put under a greater stress.

We've all heard the Super-X story in precis form and probably not a bad idea to hear more about the historical moment for the emergence of SAAMI. In the meantime, here's my old school testament about chamber pressure, recoil, and certainly "causal" relationships.

1) Pressure has no place in the calculation of recoil force. Knowing the wgt. of payload plus ephemera (wadding and powder charge), velocity of payload, and wgt of gun allows the predictive calculation of recoil of the gun.

2) Expanding gas CAN impart energy to the components of a pressure containment vessel (pressure relief valve, walls of the vessel). A shotgun at moment of firing is very much like a tank with a pressure relief valve. Expanding gas is held in containment by a piston or valve whose inertial or mechanical resistance to movement (or release) is also the condition for the creation of pressure. You could say that the vessel of containment "causes" pressure and not be much further from enlightenment than if you said pressure "causes" metal deformation and looseness in shotguns. Obviously, there is correlation of apparatus and chemical phoenomena which make possible events as disparate as: a) triggering a valve, b) overcoming the inertia of a plug or piston, c) rupturing the walls of a container, d) static maintenance of pressure in the container (in the case of hot gas, pressure in containment would decrease by dissipation of heat but would still be the classic extreme case of pressure which "causes" absolutely nothing cf. to the dramatic work done by shotguns and engines).

3) In past discussions, the mathheads and strict Newtonians have beat me about the head and shoulders until I have at least absorbed the idea that predicability of the resultant of chemical and physical events is vastly more important than which necessary pre-conditions may be termed in the vernacular "causational".

4) I still want to see the math in which peak (or durational) chamber pressure is incorporated in an equivalency of ratios to predict a single unknown (recoil force) one side of Mr. Equal Sign. Until then, I'll stick with the older vernacular that recoil of the gun as a whole and as parts (think freight cars slamming together on coupling) "causes" temporary frame deformation, barrel whip, radial and torque force around the axis of the hingepin, splaying of breech balls away from extension slots, battering of the stockhead, flexing of the stock wrist, general "Deacon's Shay" looseness, and ultimately the staggering flinch.

jack

"ultimately the staggering flinch."

This stuff is suppose to help Jack Not sure if it's to be applied prior to the 'staggers' or after?

Staggering forward of the line is embarassing, Doc! It appears to follow directly upon gun not firing or an inability to break a trigger or both but that's only mere temporal correlation and all of us here are aware that ain't what causes it. I prefer to take the cure with a "little Yuengle" from Pottsville PA or that Shiner Bock from somewhere in Tehas.

jack

Mike, there were no agreed-upon service pressure and proof standards for ANY shells or guns in this country prior to the creation of SAAMI. So . . . none, period, prior to 1926. That's not saying that gun and ammo makers didn't proof test their products; just that there were no common standards (contrary to all the other countries in the world with proofhouses).

Proof standards appear to have remained somewhat in flux, at least for a few years even after the establishment of SAAMI. LTC Calvin Goddard, I believe recognized as a ballistics expert back then, writing in "Army Ordnance" in 1934, stated that Hunter Arms proof tested 12ga 2 3/4" at 14,300. He adds that Parker followed "SAAMI standards": Proof pressure of 13,700 psi for 2 5/8" 12ga, service pressure of 9500 psi. 2 3/4" 12ga: Proof pressure 15,900 psi, service pressure 10,500 psi.

Good question about LUP vs psi, and when you go back to that era, you might well assume they're talking LUP--since that was what they actually measured then (although they called it psi). That would put the proof pressure of the 2 5/8" 12ga, following SAAMI standards, at around 15,000 psi; of the 2 3/4", around 17,000. Service pressure 10,500 psi and 11,500 psi respectively--which puts us at the current standard, with 2 3/4" shells. Additionally, Arthur Curtis--who worked at one time or another for a number of American firearms makers from the late 19th century until at least the 1930's--gave service pressure for the 2 3/4" 12ga at 9,000-10,000 psi, quite close on the upper end to current standards, assuming he was dealing in LUP.
Hope that helps.

Miller, I didn't say that the Super-X was the first 2 3/4" shell. I'm quite well aware that there were guns chambered at 2 3/4", and shells for them, before the Super-X appeared. However, it is generally accepted as the first MODERN 2 3/4" shell, using progressive burning powder. It was also a shell which increased pressure (by at least 500 psi, per Curtis) increased standard field payload to 1 1/4 oz, and increased velocity. Curtis refers to "high speed shot shells" introduced years prior to his 1938 American Rifleman article, and I'm pretty sure those are the ones he means. They certainly received a lot of glowing press, from people like Buckingham, and accelerated the changeover to 2 3/4" as the American 12ga standard. And it seems odd to me--since we certainly agree that increased payload + increased velocity = increased recoil, and since we also agree that increased recoil is not a benign force (at least on the stock, if not on the metal)--that SAAMI would stick to an antiquated service pressure ceiling rather than establishing a payload/velocity standard to protect our guns. Perhaps pressure still remains key, however much recoil has increased--and it certainly has, since WWII.

Rabbit, you're constructing a nice straw man there. I certainly never stated--and I don't believe ANYONE has stated--that increased pressure = increased recoil. In fact, if you go back the line a ways, I believe you'll find an example I gave of two loads that are identical in payload and velocity, one significantly higher pressure than the other--even though the higher pressure load uses a lighter powder charge. Powder burn rate has a whole lot to do with pressure . . . which is why, unless you reload, you can't be sure at all about pressure other than that it's within the maximum established either by SAAMI (US ammo) or CIP (European ammo).

Aha, I do believe someone or ones did provide the straw as I perceive a hint or two (perhaps from Rocket who disappeared down his silo)that non-catastrophic physical destruction of guns was somehow directly attributable to chamber pressure developed (without an intermediary called recoil) and someone sure as the devil was off on a sideways insinuation that SAAMI or IPC are on a mission to protect our guns from wear and tear by setting service pressure standards. Or maybe I'm blind?

Larry, with reference to your final two sentences, third graph, reply #547410 above, please tell me once and for all that SAAMI has or has not done something to "protect our guns" from non-catastrophic wear and tear. From the description earlier of the adoption of the 1.5oz load in 2.75" 12 ga., I would tend to believe that it has done nothing to that end; rather the dual service pressure scheme tied to chamber length was a consistent attempt to prevent catastrophic failure in two classifications of guns without obsolescing one classification by stating their inadequacy to meet the standards of another.

jack

Quote Lary Brown;


I do humbly appoligize for mis-interpreting what you were attempting to say. I now have absolutely no idea what you in fact did say. It is well to note that if the pressure was increased by 500psi as you quote Curtis as saying that represents about a 4.5% increase in pressure. On the other hand velocity of a 1¼oz load was increased by about 9% (1220 to 1330). Yet you want to say this 9% increase in force which the shell head puts upon the standing breech is totally of no significance, only the 4½% pressure increase. My personal advice to you is to stick to discussing models, grades, values etc etc of various shotguns of which you are extremely knowledgable. Leave the ballistics to someone else. I generally try to just ignore any ballistic statements you make, but I was in this discussion before you were so had little choice, as I do feel these matters need to be addressed.

Miller hit the nail on the head, as is usual, when he said "Larry, I now have absolutely no idea what you in fact did say." I must confess that I too am having trouble following Larry's posts. I think he is taking a cue from another longwinded poster who is constantly off topic and way too wordy.

My world will not end if we disagree, but I'm willing to answer questions and continue to discuss.

Guess I'm going to have to try shorter words or something. The fact that the Super-X was a "new" 2 3/4" load does not make it the first. The fact that the standard 12ga chamber length (prior to the introduction of the Super-X) was 2 5/8" does not mean there weren't guns out there with longer chambers. Just that they were in a minority. As to the rest . . . if you don't understand that there were no common standards for proof and service pressure prior to the creation of SAAMI, I don't know how to make that any clearer. Wow. . . my wife, who after many years just left a job in which her major role was to put engineer English into something "the masses" can understand, often expressed frustration. Now I can see why.

And thanks, Miller, but I can put words in my own posts. No need for you to do so. Increased payload/velocity/pressure of the then-new, hotter loads are ALL of significance in the guns in which they are used. I have a sub-6# Prussian Daly Featherweight. Even if I knew that the pressure on a 3 3/4 DE, 1 1/4 oz 12ga load were sub-9,500 psi, I would not shoot it in that gun. NOWHERE have I ever indicated that recoil is a benign force.

Rabbit, I agree with you: SAAMI has done nothing to compensate for the increased recoil generated by faster and heavier 12ga loads. Now my question to you is: Are you seeing a lot of modern 12ga guns shoot loose because of those loads? If the answer is no, then would that not indicate that there must be some other factor which is being regulated (like pressure, which SAAMI does regulate) that plays a truly critical role in metal wear? I'd add here something we have not addressed: The SAAMI pressure standard for 3" 12ga is the same as for 2 3/4" (11,500 psi service pressure), even though the shot charges are significantly heavier. Maybe someone ought to get their hands on a Ruger Gold Label and put a few thousand 3" shells through it. Volunteers?

Something else we have not mentioned in our discussion of classic American guns is that they are not equal. Even all Foxes, all Parkers, all Elsies etc are not equal. Example: Foxes had 4 different barrel weights, with a difference of 3/4 pound between the lightest and the heaviest 28" 12ga tubes. Parker made guns on several different size frames. Elsie made a Featherweight (not to mention the Long Range Wildfowl). Thus, whether an American classic double--properly cared for--could survive the increased pressure and recoil of modern American 2 3/4" loads might well depend on which Parker, Fox or Elsie you happen to own. A Fox with No. 1 barrels . . .totally different expectations than a Fox with No. 4 barrels. Although if you stuck with the hottest ammo available in 2 5/8" for that Fox, I'd say your chances are a whole lot better even with the lightest barrels.