doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 2.75" shells in 2.5" chambers

I consider firing 2 3/4" shells in shorter 2 5/8" chambers to be perfectly safe. And I'm in good company. I believe many gun manufacturers continued chambering their guns with the sort chamber and recommended using the longer shell. Here is a factory Parker hang tag for evidence. Note the chamber length and the shell length.

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I have no ides what any of the above means. I didn't see any mention of the items used in the recoil calculation formulas. There are a few around but most are similar and none include pressure, gauge of gun, bore I.D., forcing cone length or burning rate of the powder used. I have no problem accepting that the reason these are omitted is because they have no relevance.
If anyone believes that firing a 1 oz. load of shot, using a similar amount of the appropriate powder, at a given velocity, say 1200 fps., out of three 8 pound guns(12, 20 and 28 ga.) would produce anything other than the same recoil, you're beyond hope. Each shell would likely produce different pressures, 12 being least, then the 20 and the 28, the highest. Smaller bores routinely produce higher pressures. To say there would be no recoil without pressure is only true because there would be no velocity of the ejecta without pressure. If, as has been said before, the barrel was plugged so the ejecta could not move out the barrel, the pressure might be tremendous. But, there would be no recoil at all, because there was no movement of the ejecta to cause the corresponding reaction of the gun(recoil).

I do not have figures for what the closed cell pressure of a typical shotshell powder charge would produce, but I sincerely believe that if the shot charge "Failed to Move" the chamber of any ordinary gun would be "Blown to Smithereens".
Burrard gave some figures on this using the British bulk powder Smokeless Diamond, 33 grains = 3 dram measure.
This 33 grains if confined to a length of 1" of typical 2½" 12 gauge cartridge case would produce about 30.3 tons per sqin pressure. The pressure necessary to burst this typical chamber of good barrel steel having tensile strength of 40 tons per sq in would be 13.4 tons per sqin. Normal pressure for this load would be 2.8 tons.
Based on a 20 ton pressure yield strength (bbl would bulge, but not burst)it is necessary to go to about 4" before the strength of the steel excedes the maximum possible pressure capable of being generated.
All of this is based upon uniform pressure rise (No obstructional effect) for the 33 grain charge in that volume in which to expand.
This would tend to indicate that no ordinary gun could withstand a normal powder charge "IF" the shot failed to move.
This is WHY Burrard so strongly recommended "NO" shell be fired if it's "Loaded Length" allowed it to extend into the cone.
All other things being exactly equal even an extra deep crimp, requiring more force to open it can cause a drastic increase in pressure. If the loaded shell extends into the cone the opening of the crimp can be retarded causing an increase in pressure.
Max pressure is reached just after the shot begins to move & immediately begins to fall. As long as there is enough clearance for the crimp to open normally one would not really expect an increase in this max pressure. What one might well expect is a very slight slowing of the fall as it goes through the reduced dia. This would not be picked up on a normal pressure test which records only the max. It would show up if you had a trace of the pressure curve.
As to recoil the "Actual Recoil" is based solely on the mass ejected & the velocity at which it is ejected. I am at this point totally inclined to believe this amakes up about 98% of "Felt Recoil" with the remaining 2% composed of burn rates, cone shape, bore dias etc, etc, etc being of such small magnitude as to be undiscernable by Mere Humans.
There are numerous effects which can cause one to "Perceive" he has been "Kicked Harder" when in fact he has not. An example is wearing adequate ear protection can seem to "Take the Sting" out odf a "Hard Kicking" gun, but of course putting muffs over your ears does nothing to reduce either recoil or kick. An obnoxious odor from a particular powder could have a similar affect, but would not actually change the kick.
It is quite easy to get an idea in ones head, but until proven otherwise, Paint me Skeptic.

All of the elements of force, velocity have to be included as getting back to first prinicples, everything can be at least partially explained. Forget what you see, hear, feel and only consider what accurate sensors yield which can be put into a model describing the event and give quantifiable figures which really can't be argued like opinion can. Consider a group of billard balls in a circle with some type of force in the center. When all are excited, like a point source they travel in all directions with a similar velocity. Now consider the same billard balls arranged in a cylinder with finite depth and diameter and when the billard balls are excited, some go sideways while others press on forward along the path of least resistance. All have to encouter some type of reverse/negative force which seeds them to a steady state. The ones going to the sides are attentuated and reflected possibly colliding with another billard ball from the opposite direction forcing their velocity to zero. They may just be the entropy of the system but they have to be accounted for. From first principles, Force equals mass times acceleation(F=ma) and all systems strive to reach some sort of equlibrium(Thermodynamics) unless continually excited. Although I may have mixed wave and partical physics, either one should be able to expain the event. A combustion engine, a boiler, etc. are good examples and loosely are similar to what we have here with the wad be the piston which is being ejected. What we are looking for is how is the heat/expanding gas, whatever, converted into work.

Kind Regard,

Raimey
rse

I've been living a dillusional life or maybe I'm not a mere human, believing that recoil pads and gas guns facilitate a softer kick. And my handguns with their sights set up to point the muzzles downward, even they just don't recognize that they shouldn't be moving until the ejecta comes out of the barrel.

Using shot shells in chambers that are not the correct length for the shell


This question comes up innumerable times. Shotgun chamber length has changed many times over the last 100 years or so. There is for the 12 gauge 2”, 2&1/2”, 2&9/16, 3”, and 3&1/2” and I probably missed one.
In any event for various reasons individuals do not want to use the correct shell length. It may be due to availability, price or just plain lazy. These individuals search for a universal prescription that will allow them to use longer shells than the firearm was designed for. Some conduct ‘back of the barn tests’, publish the results in non-scientific journals and crow about themselves. These results are then accepted as a universal prescription, that this is indeed safe.
Some want to use standard factory loads, some low pressure loads whether factory or hand loads.
With myriad of firearms out there with different chambers, different steels, different heat treats, not to mention that many are of considerable age and have had ‘hard’ lifetimes not to mention who knows what type of refinish including heat treatment.
Couple that with the vast array of shot shells which includes the hull material, wads, powder and manufacturing techniques, it all leads to so many variations that no one can develop a universal prescription for all usage of longer shells in short chambers.
So, in effect, what you are doing when you use a shot shell not designed for your shotgun is a form of Proof Test each and every time you fire the shotgun.
SAAMI http://www.saami.org/ was tasked in 1926 by the Federal Government
• Creating and publishing industry standards for safety, interchangeability, reliability and quality
• Coordinating technical data
• Promoting safe and responsible firearms use
As such, this is what they say,

"UNSAFE ARMS AND AMMUNITION COMBINATIONS
The discharge of ammunition in a firearm that is not designed to shoot that ammunition can be dangerous and can result in serious injury or death to the user and/or bystanders, as well as damage to the firearm. This unsafe condition is caused by an excessive build-up and/or release of high-pressure gas in a firearm's chamber, barrel and/or action beyond which the firearm is designed to withstand. Therefore, in the interest of safety, you should use only ammunition of the caliber or gauge designated by the firearm manufacturer for use in that firearm. Markings indicating the correct caliber or gauge of ammunition to be used in a firearm are usually found on the firearm's barrel, frame or receiver.
One way to verify that you are using the correct ammunition is to check the head stamp on the ammunition to confirm that it matches the caliber or gauge markings placed on the firearm by the firearm's manufacturer. Some types of ammunition do not have markings on the head stamp of the cartridge. In that case, check the original ammunition packaging to determine its caliber. If you have any doubt about the caliber of the ammunition, you should not use the ammunition until you have it examined by a qualified person who can determine its caliber. Remember just because a round of ammunition can fit into a firearm's chamber, barrel or action does not mean it is safe to use that ammunition in the firearm.
Due to the availability of many different shapes and sizes of ammunition and firearms, there are countless unsafe ammunition-firearm combinations such that a comprehensive list of unsafe combinations is neither feasible, nor practicable. Below is a list of some unsafe combinations that are well known because of somewhat similar chamber and ammunition dimensions.
If the caliber or gauge is not clearly marked on the firearm, or if it appears the original markings on the firearm have been altered or modified in any way, do not use the firearm as serious injury or death could result to the user and/or bystanders, as well as damage to the firearm.
Similarly, SAAMI has not published voluntary recommended practices or procedures for re-chambering of firearms. It is possible the re-chambering of a firearm may not have been done properly or may not have been properly marked on the firearm. If the caliber or gauge marking is missing or altered in any way, you should not use the firearm. You should instead have the firearm examined by a qualified person to determine what caliber or gauge ammunition can safely be used in that firearm.
If you read the above closely, you can see that SAAMI also cannot give a universal prescription,
“Due to the availability of many different shapes and sizes of ammunition and firearms, there are countless unsafe ammunition-firearm combinations such that a comprehensive list of unsafe combinations is neither feasible, nor practicable.”

I have read all the above Posts, some are from knowledgeable individuals, some are plain drivel from Posters who know they Post drivel and some are from well intentioned individuals but not technically based.
None can supply a universal prescription to make your mind at ease when firing shot shells not designed for the shotgun in question.
The risk is yours.
Accept the risk and do what you want.
There is no easy way.-Dick
EOT

An 8 lb. SxS, O/U, and gas operated gun all receive the same recoil from a given load. Adding a recoil pad or shock absorbing type recoil reducer lets your body "feel" less of it because the total recoil is delayed getting to your shoulder. Ditto the gas gun. With a gas gun, the total recoil is broken up into 2 or 3 smaller punches. No argument. This is the difference of real "felt" or "perceived" recoil as compared to total recoil. It is deferent but, as always, the reason is within the bounds of the physics involved. Claiming differences in "felt" recoil due to different burning rates of the powder, lengthening forcing cones, overboring barrels, etc. are not likely to be true unless velocity is changed.

Great posts!

2-p makes some very good points on chamber pressure of a "solidly obstructed" breach. The other side is the 12-20 barrel burst scenario. Usually, the burst is at/near the point of obstruction, not at the breach. I think this can be calculated with the right data. I"ll look into it for the future.

"Total Recoil" is the kinetic energy or the gun on firing. It is easy to calculate if the factors are known, and they are easy enough to measure. It is the only thing I know of that correlates to what the shooter will feel when he fires the gun. It is not a 100% correlation; the difference is the subjective "felt recoil." I agree with Chuck that "felt recoil" is knowable, it is just that nobody has done the work.

Pressure contributes to recoil only as it generates velocity of the payload and powder gas. Pressure does not push back on the gun to cause recoil. Recoil is caused by conservation of momentum between the ejecta weignt and velocity and the gun weight and velocity. Recoil pads and recoiling parts within the gun don't change total recoil, but they do change the time span over which it is applied. This leads me to suspect that "felt recoil" is associated with force and/or acceleration of the gun.

Shot does not "slam into" the forcing cone or choke cone. It is at least semi-fluid and flows through these two constriction. The shot accelerates as it passes through constriction and the internal pressure drops (venturi principle). This is an orderly happening, which is why choke constriction works to reduce dispersiion.

Maybe I missed it, but I don't recall anyone saying "that they shouldn't be moving until the ejecta comes out of the barrel". "IF" they did they were wrong, recoil starts the instant the "Ejecta" starts to move. However, just for the fun of it lets assume you fire 1oz of shot, with a 35 grain (.08oz) wad over a 22 gr (.05oz) powder charge & assume the base of the wad has exactly 27" to move to the muzzle. Assume this fired from a 7lb (112oz) gun. Just as the base of the wad comes flush with the muzzle the powder gases will have filled the bore. While not absolutely correct it will be close enough for this scenario to take that half it's weight has moved the 27" length. Thus 1oz +.08oz +.025oz = 1.105oz. (1.105 x 27) ÷ 112 = .266. Thus at the instant the wad clears the muzzle the gun will have, in free recoil, moved .266". The rest of it's movement will be from the result of accumulated inertia. Now assume a standard target load velocity of 1200 fps. Even if there had been a totally uniform acceleration giving an average bbl velocity of 600 fps the charge would have traversed that 27" in .00375 sec. As acceleration is of course much more rapid nearer the chamber let's assume an average of 75% of acquired velocity or 900 fps It would then have a bbl time of .0025 sec. I have no doubt a change in acceleration rate of this magnitude would be readily felt, even though measured recoil would be identical for both. However this is a change in acceleration rate in excess of 30%. I have grave doubts that as long as the load was always adjusted to give this identical 1200 fps velocity, that any change one could make to internal bore dimensions or changes in powder burn rates, while maintaining a satisfactory load whould ever, & being extremely liberal, amount to a change as large as 5% in actual bbl time.
So small a change will require much thought & planning to even test & be certain that other external factors are not playing a more important role in what's "Felt" than an actual change in the recoil itself.