doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 2 3/4" in a 2 1/2" Chamber

"I'm glad we all now seem to be in agreement that it is not safe to put factory loaded 70mm shells in a 2 1/2" proofed and chambered gun."


This is a very prudent statement. I can only ammend to say that it would not be safe to use 70mm shells UNLESS they are those that are of very low pressure..... i.e.: Under 7000 psi.

Page 8
This was a summation of what had already been posted & it still took 3/4 more pages to agree.

I would suppose that this is progress of sorts. I keep remembering threads like this that never seemed to come to this agreement, at least not before I quit reading them.

Niklas

LB,
I don't disagree with your assertion that pressures will change on a factory made load due to powder lots. I do believe that pressures will not likely be wildly all over the map, especially for popular high quality target loads. The consumers of a STS or AA load are shooting these loads because they can depend on them. Remember who they have to deal with, target shooters are a persnickety group if there ever was one. The least little thing upsets their carefully balanced biorythem, star alignment or whatever. A shell that has a different report than they're used to will set them off for sure. A Win AA 1 oz/1200 fps skeet load will likely never see near SAAMI limits just due to Win's need for a powder loading density similarity and velocity consistancy, and that they undoubtedly spec the powder, albeit the tolerance of the powder may be different than the stuff we buy. Promo loads are yet another animal, especially the high velocity stuff with heavy shot charges.

However, to be prudent, lot testing of factory ammo should be done for pressure data if unusual pressure limits are critical to your application/safety and that mfr doesn't provide pressure data in the packaging. Which brings me to ask; why should we trust an inquiry (letter, email, phonecon, etc.) from an ammo mfr regarding pressure, if it's not on the published data for that load? I get the impression that some of the sources of shorter shells that didn't publish pressure data have provided data in correspondence to those that inquired. Why would this be more trusted than Winchester, Rem, or Federal?

Taking advantage of all the previous interchange of information and data
I would selfishly appreciate feedback on the following combination I am going to
use (no 2,5 shells locally available and I have no reloading equipment)

-Manufrance Ideal 16/65 proofed/prooved to 1100 KILOS (1079 BAR according to some
conversion tables from <http://www.convert-me.com/en/convert/pressure>
-Locally made TEC 16/67 shells, 57mm unfired length with 26grams of #7 shot,
loaded to CIP standard 570 BAR (581.2 KILOS according to same tables,or 8,267lbs)

Local CIP Proof House (yes, 3rd World country does have a proper Proof House) told me
the TEC and Fiocchi shells made locally are extremely consistent in their pressures.
A lot more consistent than the imported shells from USA or Europe they have to test.

Even allowing for a 15% increase in pressure I would be a lot lower than the proof
pressure of the gun (unless my conversions are totally off).

Thanks in advance,

JC(AL)

All of the "2 1/2" shells I have seen have in fact been 67.5 mm.
I use the Eley grand prix and impax in paper.
I have never seen any specs but I believe these are fairly mild loads.
I have used black powder 70 mm reloads in my Damascus guns without issue having read both Thomas , Burrard and discussions here before.
However I now use the paper hulls from the aforementioned Eleys,which last longer as well.
Anyone have any idea what pressures these factory Eleys produce?

GDU

Chuck, not being one of those who has corresponded directly with shotshell makers, I'd hazard a guess on why they trust the responses given them by the makers of short shells: The makers of short shells would seem to be catering to their clientele, just as are Win/Rem/Fed. And their clientele wants shells which are within the service pressure parameters of 2 1/2" chambered guns. Win/Rem/Fed, on the other hand, are in the business of producing shells, within SAAMI standards, which go "bang" reliably when you pull the trigger, deliver consistent velocity, and--with the exception of some very light loads--have enough push so that an autoloader that hasn't been cleaned since last hunting season will still function.

Horses for courses, as they say.

Larry,
'seems a little thin to put faith in when fingers and eyes are on the line. Their choice I suppose.

"Can you relate time to distance from the breech?"
Milt, this might be a question Miller or other readers of Burrard or Gough Thomas may have an answer for. I thought Miller may have quoted a reference that touched on payload travel/time/pressure at one time long ago.

Burrard shows at least one time, pressure, velocity chart but is rather hard to decipher in the early stages. This was taken with the old 33 grain bulk "Smokeless Diamond" with a 33 grain charge (3 DE) & 1 1/16oz shot charge. He did not show the actual pressure rise but simply started it at the peak @ approx 1" from breech. Both time & velocity were showing a very near vertical rise at this point with time at about .0002 sec & vel about 100fps. Max pressure was 2.8 TonSqIn. By the 4" point pressure had fallen to about 2.5 ton, vel risen to about 750fps & time to about .0007 sec. 8 inchs pressure @ about 1.25 ton, vel @ 1000fps & time @ .0011 sec. In the 30" bbl velocith reached about 1285fps, pressure dropped to under .2 ton & time was just over .0026 sec.
I don't know just how this would apply to more modern powders but suspect would be very close to a powder having a medium burn rate, say on the order of Green Dot & similar.
PS; He also stated that upon the powder being ignited the initial pressure rise was on the order of 10,000 tons per second. Of course as the wads/shot begin to move, giving increasing volume, the rise slows, then peakes & starts to fall all in about that .0002 secs. This initial point is of utmost importance & shows why crimp strength can play a vital role in developed ballistics & also why the loaded shell length should never project into the cone, possibly delaying that initial opening. Things are happening "Very Fast".

It is worth looking back as to how the concern over shell length developed.In the era when rolled over shot wad was the method used for shell closure a loaded 2 3/4 shell measured 2 5/8 It normally contained 1 1/4 ozs, of shot and the appropriate powder charge.Likewise the 2 1/2 shell was 2 3/8 inches long it normally contained 1 1/8 ozs,of shot with a proportionally reduced powder charge. The chambers of the guns at this time were machined to correspond with expanded case length [2 1/2 or 2 3/4] At the same time, forcing cones were shorter in length than todays practice. In these circumstances it was absolute folly to attempt to shoot a 2 3/4 shell in a 2 1/2 chambered gun, always assuming you could force the action to close.
Most sportsmen of the day were well aware of the dangers presented by attempting to shoot 2 3/4 shells in 2 1/2 chambered guns , this concern has been passed down from father to son. Whislt this concern is still legitimate, the advent of the crimp closed case with its reduced case wall thickness and reduced closed length, has for all practical purposes eliminated the primary reason for barrel constriction caused by the shell case length. The remaining safety problem, one that has been repeatedly stressed by other comentators is control of breech pressure.," For your safety, use only shells that generate breech pressures within the allowable limits for 2 1/2 chambered guns!"