doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com DGJ Article on Chamber Length/Pressure

What you fellows don't seem to realize in your debate is that no crimp, even a roll crimp, is shorter than the difference between a 2 3/4" shell and a 2 1/2" shell. No loaded 2 3/4" shell encroaches on the forcing cone of a 2 1/2" chamber. Do you fellows even know what a quarter inch looks like? The Garwood reference shown in snipehunter's post says it all. There is no appreciable difference in pressure caused by the extra 1/4 inch of case. That's what Garwood said in 1964 and that's what Bell said in the Finding Out For Myself articles. So I'm going out and shoot my 2 3/4" reloads in my short chambered guns like I have for more than 50 years without event. I have not spent a dollar to have chambers lengthened in that time and don't plan to in the future.

I conclude that there is danger in the citation of favorite authorities. Reread Dig's post#106799 which says it all without saying it all thrice.

jack

"My mind is made up; don't confuse me with the facts".

If the shoe fits...

JC

Well yes I know what ¼" looks like, I have in fact measured such amounts in terms of the tenth of thousandth of an inch, Thats a decimal point followed by .000X. I have also roll crimped some shells. You leave ¼" above the top wad, insert it in the crimp head & rotate while giving it down pressure to turn the end over till it meets the top wad. This leaves a double wall protruding above the top wad where had been a single one.
This means that ¼" has now been turned into about 1/8" plus a little allowance for the thickness of the paper. Now "If" the case was indeed a full 2 3/4" it has a loaded length of about 2 5/8". If you then put it into a true 2½" chamber it will indeed intrude by 1/8" into the cone. That's about 2nd-3rd grade arithmetic.
Everything I have read of either Thomas or Bell, both were working strictly with fold/pie crimped shells which use approximately ½" for the crimp. A 2 3/4" pie crimped shell has a loaded length very similar to a 2½" roll crimped case. This leaves ample room beyond the end of the case for unrestricted initial opening of the crimp, at a very critical stage in the development of it pressure rise. This is not necessarily, & most likely not, true of a roll crimp case. Not a single person has cited a reference from either Thomas or Bell, where this issue was addressed. It is indeed true that all three arrived at the same conclusion regarding loading a 2½" load into a 2 3/4" case closed with a pie crimp. This was never under discussion "By Me". It is also equally true that both Thomas & Bell cited Burrard "ONLY" in his statements which applied to a case loaded with a different load & closed with a different closure (Out of Context) & failed to even mention his reporting of the conditions they were dealing with.
It has however become painfully clear I have made a Grave & Serious Misjudgement. I had been under the impression I was addressing reasonably Inteligent people who could understand what they read, Obviously this thought was seriously Flawed.
So as far as this thread is concerned TaTa, Adieu, Au Revoir, Adious, Hasta La Vista, Auf Wiedersehn.

We have to be VERY careful when we say that so and so "says it all". The posted article by Thomas says a lot of good stuff, but it doesn't say it all--because it does not address the issue of forcing cone design. The same author (Thomas) from his chapter in "Shooting Facts & Fancies" entitled "Meeting Modern Hazards", in which he deals with reloads:

"Again, the prevalent use of 2 3/4" cases, suitably loaded, for guns with 2 1/2" chambers may be perfectly satisfactory if the guns have normal cones, but not if the cones are exceptionally abrupt, as some are, when the use of the longer case may give rise to objectionable, or at least enhanced, pressures."

Writer Charles Fergus addressed the problems he had with some of the Brit 67MM shells especially loaded for 2 1/2" guns. Worked fine for him in a newer Brit 2 1/2" gun (from the 30's), but he was blowing the ends off the shells and getting significantly more recoil in a late 19th century Brit gun which had short, abruptly tapered cones. Thomas, in the above-mentioned article, got a similar report from the owner of a French Manufrance Robust: No problems with true 2 1/2" Eley Impax shells, but significantly increased recoil and blown ends on 2 3/4" cases, even when loaded to the proper pressure standards.

Summary: At least with some guns, case length can make a difference. And even Bell's experiments showed a pressure increase with longer cases (albeit moderate), usually moderated further when the cones had been lengthened.

I've heard those fatal "tenths" are kind of tricky without stating the temp. at which measured (wink). The 1/4" of hull rolled down to a double walled 1/8" over the top card wad of the typical bp load sounds good except that I just measured overall loaded length of three of my bp shells which are loaded in expended 3" plastic hulls previously carrying Brenneke slugs prior to the season of the rack, cape, and vennison. All were loaded from an adjustable scoop powder&shot measure and have a "typical" 1/8" over powder wad, 1/2" waxed bd. wad and a thin over shot card wad adding to the stack hgt. Excess hull was trimmed off with a utility knife against a 1/4" thick brass washer lying atop the load and roll crimped. Here's the OA lgth. nos.:

2 1/2 dram + 1 oz: 2 7/32"

2 3/4 dram + 1 1/8 oz: 2 7/16"

3 dram + 1 1/4 oz: 2 9/16"

Maybe I am an ignoramous with ADD as it appears to take, in my non-hypothetical 3-shell sample, a lot of propellent and payload (more than I'd want in a gun proofed to 3 tons)to get to 2 5/8" overall lgth. Conversely, I have seen ragged pie crimps on hulls holding nitro and plastic from some of my old residenters. What can it all mean? I think it means that the stuffin means more than the thing in which stuffed certainly (except in the case of super-steep cones), but may also mean that the problem with all the arguments is too much fiddling with the marginal example. A 3 1/2" magnum stuffed into a 2" chamber (if you could do it) would sure tell us something about extremism, would it not? Too much of absolutely everything!

jack