doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Longer shells in Short Chambers

Drew,

If the pressures are not increasing what do you think is causing the increase in perceived recoil? (I'm assuming that you have not measured actual recoil?) Is it just that the AA loads have a higher velocity / load weight than the 2.5" shells that you are using? Or do you think that there is something "funny" going on that causes recoil, but not pressure, to increase significantly?

Here we go again! Only one thing increases recoil and that is greater velocity of the ejecta or the same velocity and much greater ejecta. Pressure itself does not produce recoil! Pressure is acting in all directions inside the chamber forward and backward, up and down. Or for the physics challenged, if pressure of 11,000 psi causes all that recoil in a shotgun, how could we possibly fire a 60,000psi load from a rifle? Or does a .410 with a 13,000psi load recoil more than a 10ga with 8000psi load?

Erik: this is from the thread I linked above and I've lost track of some of the sources but believe this was from Researcher

All this being said there is a good body of evidence that back in those days chambers were held about 1/8 inch shorter than the shells for which they were intended. In the recently published book "The Parker Story" the Remington vintage specification sheets on pages 164 to 169 call for a chamber 1/8-inch shorter than the shell for which it is intended. Also in the 1930's there were a couple of articles in "The American Rifleman" (July 1936 and March 1938) on the virtue of short chambers. A recent issue of The Double Gun Journal carried an article on tests showing no significant increase in pressure from shooting shells in slightly short chambers. IMHO I don't much sweat that 1/8-inch in 12-gauge guns. On the other hand when one gets a 20-gauge chambered at 2 3/8-inch likely intended for 2 1/2-inch shells I do worry about folks firing 2 3/4-inch shells in such guns.

My usual load for that 20 is 3/4 oz at 1200, 1/8 less than the AA but the same fps. I wouldn't presume to attempt to explain the perceived difference (assuming that the thin plastic case entering the forcing cone contributes little to increased pressure) but there is a marked difference. Larry Brown suggested that if the forcing cone was very short the case mouth could even enter the bore of the brl.
A squad mate asked me if I was aware that recoil was bouncing the gun off my shoulder with the AAs. The gun is less than 6 # which may certainly add to the increased perceived recoil and I am very recoil sensitive (and with a hopeless flinch) from too much shooting with heavy loads in the early days of Sporting and some medical issues.

Jerry,
You seem to have a strong grasp on this subject and I would like to ask a question without swating a hornets nest. Physics was and is not my strong suit. It seems that I hear the term peceived recoil and it is different from the actual which is pure physics. Does the perceived recoil differ because of the burn rate of powder such that the recoil is felt over a longer time span or shorter in the case of a percieved sharp recoil?
Best,
Ron

Ron: Perceived recoil is discussed on this thread from SS BB http://bbs.shootingsportsman.com/viewtopic.php?t=29480&postdays=0&postorder=asc&start=30
A couple of links are given regarding the pressure curve of different powders.
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 deprivation, stress, or anxiety.
Fun to talk about though.

Ed:

I'd start w/ a case of these:

http://www.rstshells.com/shells-best.htm

and/or these:

http://www.polywad-shotgun-shells.com/2-1-2-shotshells/

and go from there.

Agreed. I probably was not at all clear in what I was getting at. If all things are equal (velolicity ejecta, powder burn rates, etc.) save for a longer cartridge case I am trying to figure out, in that scenario what would possibly cause a significant change in percieved recoil without causing a change in the pressure. I would presume that the greater recoil (percieved) recoil is a result of quicker acceleration of the ejecta (Assume the muzzle velocity is the same, ejecta reaching that muzzle velocity in less time might conceivably result in a "sharper" felt recoil.) I am trying to figure out how the same powder, ejecta, etc. would produce a sharply different acceleration curve in such a way that the pressure was not much affected.

I do not know if this clears up my question or makes it more confused. I simply do not have the proper time to make myself clear. I definitely am aware that actual recoil is determined by velocity and mass. Percieved recoil is a bit different. I am also, of course, aware that you can increase muzzle speed without increasing pressure (e.g. by changing the burn rate) But doing so also changes the rate of acceleration of the ejecta (i.e. it gets down the barrel faster leaving more room for the gas to expand, lowering pressure, etc. etc.) And thus might influence percieved recoil. But this would have nothing to do with short or long chambers would it? (Or maybe it would. That is my question) . Rates of acceleration of ejecta do not change on their own, without something else changing.

There is one point in this that seldom gets mentioned. As mentioned, of course the load itself must be suitable for the gun in question. The British ran extensive tests on this just prior to WWII when the fold crimp shells were introduced. It was felt the normal 2½ case with the deeper fold crimp might be mistaken for the 2" shell & loaded in these ultra light guns, so extensive testing was carried out with cases of longer length. Remember that prior to this shells were closed with a roll crimp which shortened the case by only about 1/8" when loaded. The 2 3/4" case when given the roll crimp gave a loaded length almost identical to the 2½" roll crimped case. When the same load was fired from the two differeent cases both ballistics & pressure were found to be virtually identical. In spite of both Gough Thomas & Sherman Bell totally misquoting Burrard he covered this very well in his book "The Modern Shotgun". Bell's quote of Burrard appeared to be a carbon copy of Thomas, to the point I don't think he "Read Burrard for Himself" but cited Thomas. One other thing of note was, "A shell should never be fired in a gun in which the ""Loaded Length"" is longer than the actual chamber depth. A restriction of the crimp being forced into the forcing cone can delay it's proper opening & indeed can raise pressures. The point which was "Misquoted" from Burrard was his recommendation not to fire a normal 2 3/4" "Roll Crimp" shell loaded with the heavier 1¼oz charge with accompaning heavier powder charge in a 2½" chambered gun proofed for 1 1/8oz loads. With this I totally agree. Note also most American 12ga dbls were chambered for 2 5/8" cases, 16ga for 2 9/16" ones. The 20ga was chambered in 2½" length & if from a maker which adhered to the 1/8" short chambering then it is very closely approaching the length of the loaded shell. It needs a little clearence between the crimped case & the beginning of the cone for proper opening of the crimp, & I don't care what Bell said, he didn't even test that. I do shoot proper loads in shells longer than the chambers within those parameters. Since my shells are all loaded to serve as hunting loads in whatever weather should be at hand, I don't load below 7K psi even for twist or damascus.
Miller

Thanks Doc I needed that..... It is fun until someone gets their eye shot out. :p
Best,
Ron

I think it all boils down to that "ignorance is bliss". After I found out my L.C.Smith 16 ga was chambered for 2 9/16", I went and bought some low pressure shells and some reloading supplies and joined the 16 ga. Relaoders Association. Also my L.C. Smith 20 ga. has 2 1/2" chambers, so I bought some 2 1/2" low pressure shells.
My feeling is why put a lot of undue stress on an old gun if you don't have to.