The myth began with Major Sir Gerald Burrard, one of the top shotgun writers of his era. In the second of his set of books on THE MODERN SHOTGUN, published in 1931, Burrard states that it’s “distinctly dangerous to fire 2-3/4 inch 12-bore cartridges in a gun chambered for the ordinary 2-1/2 inch cases.” Yet he provides no other proof other than that statement.
Later on another famous British shotgun writer, Gough Thomas, took on this myth. He wrote about it in magazines, and later in GOUGH THMOAS’S GUN BOOK, published in 194. Since he has a lot more to say than Burrard, I’ll extract the pertinent parts:
“But in the particular case cited by Burrard, the main danger arises, not from the constriction when the cartridge is fired, but from the fact that the longer-cased cartridges he had in mind invariably carried heavier loads, and heavier loads…of necessity involve higher pressures. It is, in fact, pressure that causes the danger: no gun was ever burst by a cartridge case….To satisfy myself on this point, I arranged some years ago for a test to be carried out.”
In the test, Eley 2-3/4” ammo was fired in both 2-1/2” chambered and 2-3/4” chambered barrels. Thomas provides a table showing the results, and in both barrels the pressure and velocity results are practically identical.
But Burrard’s untested myth lives on today, as evidenced by this thread. This isn’t unheard of, because once faulty information becomes established by a popular “authority” it’s extremely difficult to dislodge. I even known people in the American ammo business who were surprised when they ran the same basic tests, with results identical to Gough Thomas’s. The most recent test one I heard about was performed by Winchester Ammunition used an old 2.59” chambered 16-gauge Sauer—in which 2-3/4” ammo produced the same industry pressure and velocity specs as it did when shot in 2-3/4” chambers.
The reason pressures don’t rise is a 2-1/2” or 2.59” chamber’s forcing cone is long enough to contain the unfolded crimp of a 2-3/4” shotgun shell. Thus the wads and shot are NOT constricted inside the actual bore by the case. Yet despite plenty of pressure-tested proof going back more than half a century, this myth continues to march on.
satx78247 , while I have plenty of respect for C.E. Harris, he may or may be aware of the pressure tests I cite. As noted above, even many professionals in the gun business don’t.
Erich, so you “gather” from Doublegun “it does raise pressure.” I’ve spent some time on that site now and then, and would be very interested if any of the people you “gathered” it from provided any proof. My guess is they’re still parroting Burrard, even if they don’t know he’s the original source of the myth.
Again, here is my original post on this thread:
“It's been proven many times, by actual pressure-testing, that firing 2-3/4" ammo in chambers as short as 2-1/2" doesn't raise pressures. It has nothing to do with "how the maker bored the shotgun barrel." But this myth continues to wander along.
The only possible problem is modern ammo loaded to higher pressures than old guns can handle. But it has nothing to do with whether the chamber is 2-1/2" or 2.59".”
